Honda 250sx still bogging

[mmiguy2103]

Ok guys another notorious 250sx carb issue here. So i have a 87 250sx that i have completely rebuilt, I am talking everything was dissembled and cleaned or replaced. all new bearing through out the entire machine. Started right up with the carburetor that i had cleaned with a 48 hour soak in a ultrasonic cleaner all new jets. cleaned every orifice and blew it out etc. So it idled great.. but if i gave the throttle a bump at all or a full throttle shot it would bog and die. If i kept the choke on it would idle high and would rev up way better when slamming on the gas. so i cleaned the carburetor again with another 48 hour ultra sonic soak and manual cleaning of the entire thing.. again new jets were installed. Installed this again and still the same issue.

So upon great reviews i decided to send my carburetor out to Flyinfw as he seemed to know a lot about these carbs. my experience with him was great I got my Carburetor back and installed it. it seemed to run better.. but i wasn't able to get out and ride. I am finally getting more time now to ride and started her up.. she started up great and idled perfect.. but now the bog is back 100% it almost cuts out whenever i press the throttle..again if i pull the choke and have it idle higher with the choke it seems to want to rev up way better when smashing the throttle. its to the point where its completely not rid able. its either idling or full throttle after 10 seconds of slowly easing the throttle .

So what gives? what am i doing wrong here.. would a faulty CDI cause this ? i have checked spark, and its great and powerful when cranking. coils tests perfect.

i know ALOT of 250sx and big reds seem to always run like crap. I owned one brand new back in 86 and i remember it running amazing with absolutely no bog whatsoever.

So any input is welcomed


Chris

[Baba Yaga]

Pilot jet/circuit, or the carb was not reassembled correctly.

[mmiguy2103]

Pilot jet/circuit, or the carb was not reassembled correctly.

I am 100% sure the pilot circuit has been assembled correctly and is fully clean and clear. everything is to Honda specs as far as jets go and adjustments

[mmiguy2103]

Tomorrow i will upload a video to help show my problems i am having

[ps2fixer]

Maybe adjust the needle clip location down a slot and see if it's better or worse. One tuning doesn't work for all locations and elevations, sounds to me the main/needle is too lean. Also doesn't hurt to do a plug check, white powder is lean, black is rich, light brown is normal. The choke testing supports the idea that the main is too lean (or possible plugged/restricted, but I'm sure FlyingW checked it out well).

Also, an intake leak could cause issues too, is your carb boot good, good O-ring etc? Is the compression up to par?

I have an 85 250es, ugliest machine I have, but it always starts first kick, revs out great, it's not inherently a 250es/sx problem. I've heard the 85's were "hard starting", either this one has a later carb, or the jetting has been adjusted for easier starting. It's been sitting for a bit so I get to check what's in it pretty soon, hopefully jets were replaced, not drilled out.

[MrConcdid]

Is your choke hooked up, My 250sx is cold natured, while cold you can't rev it. once warm its perfect.
Does your choke hang up?
MrC.

[350for350]

I am 100% sure the pilot circuit has been assembled correctly and is fully clean and clear. everything is to Honda specs as far as jets go and adjustments

Yes, but you said that it seemed to run better (after Flying W did his thing) and then you couldn't get out and ride it. How long did it sit? It's possible that the pilot jet is partially or fully plugged up.

[shortline10]

Make sure your choke assembly is installed correctly , seating all the way down , if not it will have your symptoms .
As far as I know Jim test all his carburetor rebuilds on a running test motor before he ships them out .

Also 2 or 3+ month old corn fuel will have your symptoms . Try fresh fuel .

[mmiguy2103]

Thanks everyone for the ideas.

So the fuel is Fresh non ethanol fuel. I didn't store it with fuel in either the tank of the carb.

I did make sure it was warmed up.. I always remembered how cold blooded these guys were lol it ran for about 15 min idling with a box fan on it then i tried to take it around the block a few times.. sputtering.


I am very confident that there is no obstruction in the carb as both me and flying did our thing.. and he said he had it fully running great on his test bench engine.. so that leads me to confirm that.

I am leaning towards the choke maybe.. it is a new choke rebuild kit. it does feel like it is fully seated as far as i can tell.

I think i will get to my shop today to take a quick video to help show you guys what its exactly doing. of course carb issues are hard to explain in a written way.

also does anyone think a bad CDI or partly failing CDI would produce this issue?

[shortline10]

I have seen plenty of bad CDI boxes were the motor would not rev up , only idle but not on this model .
Try wiggling the ignition switch with the key back and forth while it’s acting up , could be a poor connection their , same with the handle bar switch .

[ps2fixer]

FYI, the kill switch and ignition switch should have NO CONNECTION for the ignition system on those machines. Completely disconnect the wiring if those parts are suspected. On a DC based CDI that can be an issue because the power supply comes through the switches, but on an AC CDI system the kill wire is shorted to ground to kill the engine. All Honda 3 wheelers have AC based CDI's or are points engines (effectively the same thing, just uses a mechanical switch instead of an electric one).

The lighting system has nothing to do with the ignition for AC CDI systems, can completely disconnect the lighting wires and have no effect on ignition. Some DC systems uses the AC power from the stator's lighting coils to detect the engine running/spinning like on a TRX300/FW.

[mmiguy2103]

ok guys i was able to get to my shop today and get the 250sx all warmed up and take a video of whats going on.. now i also want to state that when i am actually driving this guy around the symptoms seem to get worse.. hard to tell

here is a link to my you tube video of it .

https://youtu.be/rs5bcB5vbYk

[MrConcdid]

That hanging Idle may be the culprit, I think its going lean and diying.
Check the float height and the choke circuit.
P.S. Beautiful SX

MrC.

[ps2fixer]

That machine really did turn out nice, best 200x front end conversion I've seen, it actually looks natural on the machine. I might have to copy the parts list you use =).

The hanging idle is defo something to check into, I have a 250es that does that, and it's also lean on the high end, does the same thing, floor it fast and it dies. I haven't messed with it though, pretty sure in my case it's the needle jet adjustment but haven't done it to solve that exact problem.

All of my 3 wheelers if you really stab the gas, they all stumble. None of them have an accelerator pump which off sets that issue. For the 350x, the 400ex carb is known as an upgrade, but the biggest reason people go for it is the accelerator pump feature. Basically if you stab it too fast, it doesn't have enough vacuum to pull fuel from the carb and it goes lean for a bit then ramps up once the fuel gets to the engine. Your machine seems to run about the same as my best runners, but it's hard to judge how fast you're hitting the throttle.

If the stabbing the gas and not having it stumble is what it should do, I'd like to see a video of a Honda 3 wheeler showing that off with out a carb swap. I don't think any honda 3 wheeler had an accelerator pump.

Anyway, seems to me your carb is dialed in pretty close. I'd check the throttle cable routing and make sure it's returning freely (good spring etc). That hanging isn't normal for sure but I can't think off the top of my head what causes that besides the cable holding it open.

[yaegerb]

I would try the following.
1. Check fuel flows freely into carb
2. Ensure nothing is clogging the air filter or pathway
3. Ensure your muffler isn’t clogged somewhere
4. Try revving with fuel cap removed. Your vent may not be working.

Let us know if those have all been checked.

[mmiguy2103]

Awesome ides guys let me update to what i have checked etc.

-Fuel flows perfectly into the carb as i have had the bowl off and checked by pudhing up and down on float. I also have the float height right where it should be.

-Air way is completely clear as everything is new.

-exhaust is fully clear

-Fuel cap has no effect.. on or off.


Thanks for the compliments on this 250sx.. its was built using all parts. its so clean i dont want to ride it haha

so anyways i have the stock jetting in this what would you guys think to do.. i did try to change the needle clip both up and down one position and didnt see any change.

the accelerator upgrade to the 350x make sense to me. so i agree it seems like its way lean when i punch the throttle. how can i fix this ? I remember getting the same model 3 wheeler brand new when i was 14 years old and i never had this issue ever with it bogging and dying like this

[mmiguy2103]

That machine really did turn out nice, best 200x front end conversion I've seen, it actually looks natural on the machine. I might have to copy the parts list you use =).


Thanks alot! i always hated the ugly front fender on the 200x. it was just to wide and stubby. the 250r fender works perfect and give it a way sportier look.. and the 350x headlights... i mean they just look badass lol

[ps2fixer]

Yea, most of the 200x front ends I've seen just look off to me, might just be the 200x fender/light or something. I have plans for building a 250sx frame up but using almost no 250sx parts lol. Longer swing arm, 350cc engine, 200x, 250r, or 350x front end. I have a long long ways to go, but I have the frame and some basic parts. Won't be a pretty build, it's going to be a rider and I'll be riding it hard if/when I finish it =). End goal is effectively a shaft drive 350x.

I haven't followed the 250es/sx carb upgrade options much, but I suspect a 300ex might be an option, or maybe some newer 250cc quad before EFI was introduced. Intake size, air box size, and length are the major things to try to match up. Venturi size should match the performance of the machine, if it is otherwise stock, I'd target keeping it as close as possible to the stock size.

I'm interested to seeing the ideas that pop up in this thread, maybe I've just been living under a rock and my machines all need some carb work lol. I don't have any problems riding fast and hard with the carbs I have, but I don't stab the throttle as fast as possible either and under normal riding, I never notice any bogging. I can't recall if the machines will completely stall if jabbed really fast, but I do know they stumble a bit.

Here's a video I found about the accelerator pump. Little hard to understand him, could use CC to get an idea what he's saying. This is how I understand the situation as well. Also, this is from the era when you'd pump the throttle for starting a cold engine (extra fuel). The people pumping the throttle with an EFI engine don't understand how things work and could be flooding the engine. EFI systems also have a "clear flood" mode, if you floor the throttle and crank, the fuel injectors are not fired and helps dry the cylinder and spark plug, same logic with a carb, but a little gas is still getting in the engine, but the vacuum is so low it's very lean or "dry".


https://www.youtube.com/watch?v=0bMn8ehMi6s

[yaegerb]

Awesome ides guys let me update to what i have checked etc.

-Fuel flows perfectly into the carb as i have had the bowl off and checked by pudhing up and down on float. I also have the float height right where it should be.

-Air way is completely clear as everything is new.

-exhaust is fully clear

-Fuel cap has no effect.. on or off.


Thanks for the compliments on this 250sx.. its was built using all parts. its so clean i dont want to ride it haha

so anyways i have the stock jetting in this what would you guys think to do.. i did try to change the needle clip both up and down one position and didnt see any change.

the accelerator upgrade to the 350x make sense to me. so i agree it seems like its way lean when i punch the throttle. how can i fix this ? I remember getting the same model 3 wheeler brand new when i was 14 years old and i never had this issue ever with it bogging and dying like this

Try tapping your CDI with the plastic end of a long screw driver while you are trying to rev it. I say tap, a pretty good hit.

[yaegerb]

Awesome ides guys let me update to what i have checked etc.

-Fuel flows perfectly into the carb as i have had the bowl off and checked by pudhing up and down on float. I also have the float height right where it should be.

-Air way is completely clear as everything is new.

-exhaust is fully clear

-Fuel cap has no effect.. on or off.


Thanks for the compliments on this 250sx.. its was built using all parts. its so clean i dont want to ride it haha

so anyways i have the stock jetting in this what would you guys think to do.. i did try to change the needle clip both up and down one position and didnt see any change.

the accelerator upgrade to the 350x make sense to me. so i agree it seems like its way lean when i punch the throttle. how can i fix this ? I remember getting the same model 3 wheeler brand new when i was 14 years old and i never had this issue ever with it bogging and dying like this

Try tapping your CDI with the plastic end of a long screw driver while you are trying to rev it. I say tap, a pretty good hit.

[Baba Yaga]

If it runs and responds perfectly normal with the choke on, then you definitely have a mixture/jetting issue.

Not sure why you're stabbing the throttle so quickly; they can't usually richen quick enough for those throttle settings.

Do you have another carb to try? Would help in troubleshooting.

[mmiguy2103]

If it runs and responds perfectly normal with the choke on, then you definitely have a mixture/jetting issue.

Not sure why you're stabbing the throttle so quickly; they can't usually richen quick enough for those throttle settings.

Do you have another carb to try? Would help in troubleshooting.
I have been riding for 30 years.. 100's of different machines. I have never not been able to punch the throttle. There shouldn't be any bogging like I am having. A bog like that can cause accidents. And like I have stated before I had a brand new off the show room floor 250sx when I was a kid and it never bogged no matter how you drove it in any condition..

And no I dont have a other carb to try

[mmiguy2103]

I will try tapping cdi box and wiring just to rule it out, before I reinstalled the wiring harness I had made sure to check resistance of every circuit to make sure the harness is good

[Flyingw]

This is a common problem with the QA series carbs. I have investigated this problem for a long time and I have yet to come up with the cause. Most QA series carbs do this in varying degrees meaning some will completely stall when the throttle is stabbed off idle and some will just stutter. I have take several carbs with this problem and replaced one part at a time and nothing affected the problem leading me to believe the problem is in the body. What Ive been telling guys is not to stab the throttle right off idle. Give it gas and once the motor gets going then hit it so until somebody can figure out what the hell is causing it then that's all we can do. My carb even does that. The QB series carbs which is the same basic carb but Honda added an accelerator pump so I'm thinking its a design problem but that doesn't explain why some carbs don't do it.

[Flyingw]

Some have suggested when the throttle is stabbed the carb goes lean but I disagree with that assessment. I am more in the thinking the problem is a vacuum block. Also, the ES and SX carbs have a primary jet whereas the 350X and TRX250 carbs don't. I have tried the TRX carbs on my test stand with mixed results but the last one I ran had no stall whatsoever. I was laying in bed last night thinking about this problem and I wonder if the primary jet might be causing the problem or at least contributing to it. I need to look through my carbs to see if I have a TRX carb so see if a different carb would have the same results as the last one. Also, I want to put together a carb from a body that I know has the stall problem and block off the primary jet to see what I get.

[ps2fixer]

That info I stated is based on what my dad has told me which is was an ASE certified automotive tech (he grew up working on carb'ed vehicles). Either case, I'm interested to see what you can find.

So what exactly do you mean by vacuum block? When you go at low rpm and open the carb wide open, the venturi has very little air pressure drop across it which causes a lack of fuel flow atleast as how I understand it. Solution is an accelerator pump to off set the fuel demand for those situations. I think another option is a smaller venturi size but then you're limiting max rpm performance (more restricted intake). From my understanding, that's why cars have check valve/one way valve on the vacuum line going to the brake booster, so it can maintain the highest vacuum possible for the most braking assistance.

Here's a vacuum gauge on an EFI car engine to visualize, never used one but I kind of want one now lol. You can hear that engine bogs a little before taking off too.


https://youtube.com/watch?v=SdlNwm8OHco&t=223

Anyway, I'm not trying to argue or anything, I truly want to learn from this, rather me being right or not isn't my focus, just trying to present it as I understand it.

[Flyingw]

If you look at the physics of what happens when the motor goes from a steady idle to wide open throttle in less than a half second I come up with vacuum block. It leads me to believe the sudden burst of vacuum prevents fuel from being pulled from the bowl. I don't know, something is strange about this problem.

[mmiguy2103]

again really appreciate all you guys giving your ideas and what not.. I am a grad from MMI in Florida and worked in a shop for 6 years and it give me a headache thinking about it haha

I am kind curious to see what would happen by swapping in a 350x carb into it with the stock 250sx jets. i can source a used carb locally for about $100. i might try that after this whole virus world coming to an end things stops lol

So obviosly its a totally different machine. but i have a 06 suzuki drz400s and it had a CV style carb in it . i had basically the same kind of bogg when i would snap to full throttle but it never would die it would just hesitate. then i swapped out and put in a 39mm FCR mx carb with a accell pump.. and OMG BOG GONE and it Ripped!

[ps2fixer]

I'm not sure how much things are effected by the venturi size, you'd be going from 27mm to 31mm. Also the jetting probably won't work using the 250sx jets, I'd think you'd be better to start with the 350x stock jets if my thinking is right (never done a carb size swap like this). Both of my 350x's do the same thing, so doubt you'll get the benefit you're looking for. The 400ex carb is 38mm venturi but has the accelerator pump.


I have a table of carb numbers in a table at the link below. The QA series carb is the 250sx/es and 350x type. The 400ex type is the QB series. Maybe a carb from one of those machines would be more ideal like the 91-92 TRX250X or the TRX300EX carbs. I'd personally go for the 300ex ones since they are much newer and made for a much longer time, should be tons of parts on the market and most/all parts available from Honda yet. Took a quick peek on bike bandit and the 2009 version of the QB 300X carb is all available including it as a whole unit for $273.

https://atvmanual.com/honda/atv-oem-carburetor-throttle-body-identification

[Baba Yaga]

I have been riding for 30 years.. 100's of different machines. I have never not been able to punch the throttle. There shouldn't be any bogging like I am having. A bog like that can cause accidents. And like I have stated before I had a brand new off the show room floor 250sx when I was a kid and it never bogged no matter how you drove it in any condition..

And no I dont have a other carb to try

Don't need your resume, just trying to help. I have 15 trikes and none of them have instantaneous throttle response. But if it bogs with even moderate throttle application, that is an issue. Your issue is nothing to do with CDI.

If I were you, I would take it to a bike mechanic that knows carbs well.

[yaegerb]

again really appreciate all you guys giving your ideas and what not.. I am a grad from MMI in Florida and worked in a shop for 6 years and it give me a headache thinking about it haha

I am kind curious to see what would happen by swapping in a 350x carb into it with the stock 250sx jets. i can source a used carb locally for about $100. i might try that after this whole virus world coming to an end things stops lol

So obviosly its a totally different machine. but i have a 06 suzuki drz400s and it had a CV style carb in it . i had basically the same kind of bogg when i would snap to full throttle but it never would die it would just hesitate. then i swapped out and put in a 39mm FCR mx carb with a accell pump.. and OMG BOG GONE and it Ripped!


Did this carb bog like this before you took it apart?

[danbur55]

Have read that needles have different tapers just wondering if a different taper might change things. Also the ramp on the slide?? Thinking outside the box Also the frame tubes to air box you might run some stiff wire just to verify that there is no obstruction even after all you’ve done

[mmiguy2103]

Did this carb bog like this before you took it apart?

oh yes this was a problem for a long time

[mmiguy2103]

Have read that needles have different tapers just wondering if a different taper might change things. Also the ramp on the slide?? Thinking outside the box Also the frame tubes to air box you might run some stiff wire just to verify that there is no obstruction even after all you’ve done

i have verified that the entire intake even through the frame is open and flowing perfect. thanks for the idea! yes needles have different tapers.. I am using all the stock jets and jet needle. all new from Honda verified. everything is stock and i am at about 50 FT Above sea level.

[ATC King]

The carburetor bodies are a cast piece, that requires machining to finish. The fuel and air circuits are drilled into the carb body, and the ones drilled through or from the outside, require a plug to seal the passage. These are the things that look like little brass BBs.

That carburetor was a mass produced item, made over thirty years ago. Those plugs can loose their seal, or may be they never had a good one to start with and it just got worse.

This is an actual problem on other carburetors. Some are known for it, while it's seldom a problem on others, but any carburetor with presses in plugs can develop a leak there.

A hanging idle that you can't get rid of could be a symptom of it, if the idle circuit is sucking in air. That would be the little BB on the very end of the carb on the engine side.



The quickest fix is usually a dab of epoxy over the offending seal. In this application, I think a dab of clear fingernail polish would actually work, and I'd put it over all of the sealed passages on the outside.

That's simple, inexpensive, and if done cleanly, it won't be noticeable.



The other thing I'd do, is check the valve clearance again.

[ps2fixer]

I never thought about those plugs leaking, I bet you're onto something there.

[MrConcdid]

You could be on to something "The Mr. King"
I have a factory carb Keilin on my 200m, I cleaned it 3 times, I put every component of a Shindy rebuild kit into it. and it still did the same thing. wouldn't idle, hanging idle also.
Just when I thought I figured it out it acted up again. I tried everything richer/ leaner etc, etc.
I cleaned and rebuilt a different OE carb the same way I have always done it, and put it on, The bike runs perfect now, no hanging idle, it idles great now.

So, do you have another carb to swap just to rule out a few things?
Even an ebay carb would eliminate some things like , ignition, timing, leaks, intake ect.
Why not do the upgrade to the 300ex/400ex carb as a test, you may like it.

MrC.

[yaegerb]

My .02....if everything else checks out I would think the carb is still suspect. The hanging idle is what leads me to believe it’s truly carb related. You can clean up a hanging idle be richening or leaning the idle circuit. Honestly at this point I would get a different OEM carb and rebuild it. Especially since you had this problem before disassembly.

[Flyingw]

I am sending MMIGUY a Chinese carb I bought years ago that runs great. This carb is an 86/87 clone and when I got it, there were a few minor discrepancies but its always ran good. I asked Chris if he would send back his carb and I am going to explore the sealing ball suggestion made by ATC King to see if it makes any difference. That's one thing I never thought of. Over the years people have asked a lot of questions about my test stand so here is my very first You Tube upload of the test of the Chinese carb for you motor heads. This test stand has been an invaluable tool for me over the years. https://www.youtube.com/watch?v=YGnuNSzyfr4

[mmiguy2103]

I am sending MMIGUY a Chinese carb I bought years ago that runs great. This carb is an 86/87 clone and when I got it, there were a few minor discrepancies but its always ran good. I asked Chris if he would send back his carb and I am going to explore the sealing ball suggestion made by ATC King to see if it makes any difference. That's one thing I never thought of. Over the years people have asked a lot of questions about my test stand so here is my very first You Tube upload of the test of the Chinese carb for you motor heads. This test stand has been an invaluable tool for me over the years. https://www.youtube.com/watch?v=YGnuNSzyfr4

again thanks so much!! i am excited to see what this chinese clone will do!

[ps2fixer]

Neat setup for the test bench, thanks for sharing. I originally thought you legit installed the carbs on a 250sx/es machine as a whole. Since this is a true "bench test" type of setup, one upgrade I could see is going for an exhaust gas analyzer and/or O2 sensor and a tach that's a bit more responsive.

I think the bog is most noticeable from idle and flooring it. Mid to max haven't really had bog problems. I'm only able to really bog my engines by basically slapping the throttle to go from 0% throttle to 100% almost instantly, like normal riding position I might get a tiny bit of a bog but nothing to even bother with. Only exception is one machine I have that has a minor bog problem and the idle hunts a little, so really interested in what we can find out in this thread =).


Personally, I think the O2 sensor setup with a fast responsive voltage meter (one that doesn't average over time ideally for quick response) would give good tuning experience besides by ear like the video below. This is for a car/truck engine, not sure how well one would work on a small atv engine. Could look into what the EFI style atv's run and try one of their sensors. More wires just means it has a heater to get to closed loop faster. Clearly not the typical setup for the average person.

Now I want to look into O2 sensors a bit more and see what the distance requirements are from the engine that they work well at. Maybe the exhaust flange location could be used as a temp hookup with a short adapter between exhaust and head pipe to tune the carb. It's a pretty standard interface so it could be somewhat universal for any Honda atv.


https://www.youtube.com/watch?v=weJUxr11CGU



My dad has one of the sun engine testers like the big one in this video, don't know much about it but he has to replace all the vacuum hoses on it and re-calibrate it. He's had it for atleast 20 years that I know of. It's like from the 60's era if I'm thinking right. He wants to fix it up because he's been getting into building chain saw engines up and wants to tune besides ear and rpm to make sure he's doing it right. Too lean on a chain saw is a bad mistake. I'd like to use it for atv engines and such =).

https://youtube.com/watch?v=lEDMuzj4GKM&t=83

[Flyingw]

The tach I have is inductive and all I use it for is setting the idle speed so it works just fine for the way I use it. As you can see, the setup is exactly as it is in the frame. Stock airbox, stock muffler, and a cut down electrical system. Whats cool about this setup is I mounted it to the top of a Harbor Freight 5 drawer toolbox. I didn't want to lose the storage area under the lid so I installed four linear actuators and a 12v battery so when I need access to the tools under the lid, I hit a switch and the whole thing rises up 10". I put tools under the lid I rarely use so I'm not in to it too often.

[Flyingw]

Here's my second YouTube video upload of how I raise the lid. https://www.youtube.com/watch?v=Z7IMxK5F87E

[ps2fixer]

That's quite a setup now. What do you do about say a 350x carb when you rebuild one of those? Test it on the same engine?

Those actuators don't sound too happy with the weight, but they work =). I wonder if adding long enough struts to it would help take some of the load off them. Probably not worth doing, as the saying goes, if it's not broken, don't' fix it.

I need to get further with my CDI research stuff, I suspect you'd probably be one of the people that would benefit from something like that (able to test most/any Honda CDI).

[Flyingw]

Each actuator is capable of lifting 300lbs so there is 1200lbs of lifting power there. I test the 350X carbs the same way and I don't have to make any changes to the test stand.

[ps2fixer]

I suspect a 400ex carb could be used on a 250es/sx then.

I should start a build thread (a very slow one). Going to attempt a 350d engine swap into a 250sx frame with some mods. Should be a fun build and the 350D uses a QA series carb too, so probably switch to the QB series like the 400ex carb.

[yaegerb]

Here's my second YouTube video upload of how I raise the lid. https://www.youtube.com/watch?v=Z7IMxK5F87E

That whole setup is so cool

[ATC King]

Flyingw, it'll be interesting to see what you find out.


There's always a chance for something out of left field.

[Flyingw]

Ya King, I'm curious too. I have changed every part in a few carbs and the problem went unchanged so it left me scratching my head. I will certainly post up the results.

[MrConcdid]

Yes, I think we all stand to learn something.
MrC.

[MrConcdid]

Any Updates?
MrC.

[Flyingw]

I got the carb back from MMIGUY but haven't had to look at it but I will this weekend. My plan is to run it then seal up all the seal balls (Brass BBs) with a two part epoxy then run it again to see if there is any difference. I'll report my results sometime this weekend.

[MrConcdid]

I have one, that I have gone through many times, I am ashamed to say, it just wont act right, each time I try it on different bikes, I end up taking it back off, putting a different one on, and they run great. I think there is a casting that fails with age or heat cycles, that cause a lean issue, but that just a guess.
I hope you find the issue.

MrC.

[Baba Yaga]

I am sending MMIGUY a Chinese carb I bought years ago that runs great. This carb is an 86/87 clone and when I got it, there were a few minor discrepancies but its always ran good. I asked Chris if he would send back his carb and I am going to explore the sealing ball suggestion made by ATC King to see if it makes any difference. That's one thing I never thought of. Over the years people have asked a lot of questions about my test stand so here is my very first You Tube upload of the test of the Chinese carb for you motor heads. This test stand has been an invaluable tool for me over the years. https://www.youtube.com/watch?v=YGnuNSzyfr4

That initial bog when snapping the throttle, is like pretty much every ATC I've seen.

[mmiguy2103]

Hey everyone havent been able to get on here in a bit .. a update from my end.
I got the chinese clone carb from Flying and swapped it out.. this is a night an day difference. from a dead idle i can completely go full throttle instantly and there is almost no bog. the bike also does not die like it was doing with the stock carb ever. I went out and ran the hell out of it for about 3 hours.. and never had one bog or issue with it.

So i am curious what you will find flying. I had multiple times sprayed cleaner around the carb while running to check for and change in idle for air leaks.

[mmiguy2103]

see I have a completely different view.. I have owned 12 different honda atcs. some brand new from the factory back in the 80's and some used. i never had a bog like that. maybe one out of every 100 times you chopped full throttle. but now that i see a huge diffence in swapping out my stock carb to the chinese clone and its running perfect i am curious what flying finds

[Baba Yaga]

Glad it's working better. Even in the YouTube video on his running setup, you can see the hesitation when the throttle is hammered, which is normal. Of course, if it's much worse than that, it needs attention.

[Flyingw]

I had a busy weekend rebuilding six carbs. I had two 85 SX carbs, one 86/87 SX carb, and three 85 350X carbs and every single one of them had the same stall on throttle stab off idle. Every one of them. Unfortunately I did not have time this past weekend to work on MMIguy's carb but I will get the brass balls sealed up this week sometime. More to follow.

[Flyingw]

UPDATE: I sealed off each sealing ball with some two part epoxy and ran it. No change to the stalling problem. I was really hoping the carb would have improved but as I said, no change so back to the drawing board.

[ps2fixer]

Maybe it's a small air leak in another area, like the shift the butterfly is on or the plunger for the main jet? Just random ideas to give a shot. Erosion could be a possible thing on the machined passages in the carb, I would think if that was the case it would be too rich if anything. There has to be something to put the blame on.

[Flyingw]

I wish I could get an unused slide to see if that changes anything and they are still available at 56.00 bucks. The slide has a Teflon coating and does wear but i'm not going to pay that not knowing if its going to change anything.

[ps2fixer]

You could always buy a chinese clone carb that has the same slide size, but then you run into low quality parts and it's not really much cheaper as a whole carb. If you have a 350x carb with this problem, I have a chinese carb slide I could probably ship you to try out. I'll have to check to see if the OEM carb and china carbs are the same or not. Some parts are exact matches, some are redesigned maybe from a new honda carb layout or something. Have a bright idea of buying China carbs and parting them out for the usable parts on OEM carbs. Reasonable prices for parts that are next to impossible to get in good shape with out buying a whole carb, like the float bowl matches up and works on the OEM carb. China carb is about $70 though :-/.

[ATC King]

Thanks for the work. That puts the idea to bed and you may be the only one who's tried that.

[Flyingw]

I should have thought of that Fixer before I sent my Chinese carb to MMIguy while I troubleshot on his carb. It is an exact match to the OEM carb although I never put calipers to each part to see if there were any dimensional differences. I have in the past swapped out slides with no changes in the bogging problem so that's why I dismissed the slide as the culprit. If I ever get that carb back from MMIguy, I will surely do that for sure.

[ps2fixer]

The slide is the same, but the arm on mine vs the 350x carb is mounted at a different angle, and the linkage system from where the cable goes on to where the slide is lifted isn't the same, even the shaft sizes into the carb body is different. I'm not sure what it's based on, but that section isn't a 350x carb base, maybe a QB carb or something like that. Just about everything else is spot on though. I have a carb apart if you'd be willing to throw a little money my way for it, nothing big, just cover that part of the carb cost + shipping, but it is a 350x clone, so the slide I'd guess is a different size than the 250es/sx carb. I also did the same thing for a 400ex china clone carb vs the 350x oem carb, some parts interchange, but there isn't much that matches up, I think it was a cheaper carb though, like $40. I'd dare to say anyone with a 350x, grab the 400ex clone carb, put in quality jets, and buy an OEM rebuild kit for the gaskets and such and it should be a reliable carb. Basically replace the important stuff and the rest being "ok" quality I'd think would work out fairly well. Haven't really messed with the China carbs much, just physical testing the parts on an OEM carb body.

Another reason I bought the China carbs was because I've been trying to find a solution for the atc250es/sx machines for new left handle bar controls, so far all of the choke systems are not right and don't pull the cable far enough. Next best thing is delete the choke cable, aka put the 350x style choke lever on the 250es/sx carb and run the same left handle bar switch set I use for other machines. Probably be like $90-100ish for the kit, but I have to get rid of the other carb parts, else I'd have to charge the full carb price on top of the switch price.

Oh another big change on the china carb is the pilot adjusting screw changed. The china one has the housing extend further, so the O-ring design is higher up, so in the OEM carb it doesn't seal the threads, but besides that it appears to function, just wouldn't be right. Sadly the only way to know if stuff works is to buy it and try it.

If there's anything you need me to test or measure, let me know. I have a couple 350x oem carbs, one china 350x clone, and a 400ex clone and a 250es oem. Most are pulled apart to just about nothing but a pile of parts so prime time for measuring and such.

[Flyingw]

There's a guy on FB who said he may have one so I'm waiting to hear back from him. I do know the Chinese ES/SX clone MMIguy has on his bike has different linkage and the butterfly shaft is different other than that, it was a good copy. I have lots of OEM 350X, SX, and ES carb parts on hand. There is no rhyme or reason as to what carbs do it and which one don't. Its across all year carbs and all models that use the QA series carbs. The only thing common is the body core.

[oscarmayer]

i produce a performance CDI that helps a ton with these issues. www.mikesatvfix.com gives more info. a lot of guys have been running my CDI now and love them. they are Japanese designed and produced in TW for costs but the QA is still Japanese guys. anyway, i have a new shipment coming in about 3-4 weeks. normal cost os $95 shipped lower 48 states. there is a $10 discount for pre-orders. paypal is mike@mikesatvfix.ocm if your interested. several can chime in on how their personal experiences.

[MrConcdid]

Whats the compression on this engine? could you check it again?
I see the quality of your build, but still trying to rule things out.
How does the plug look at a WOT plug chop? this could explain some things?

Since you have tried several different carbs let move passed that. things to also consider
1. Fuel flow ie tank vent open/closed? fuel line size?
2. fuel rating? age?
3. Timing? could you be off a tooth? may be a valve opening to soon?
4. run a leak down test

I know that all sounds like a lot of checking, but having the same problem with different carbs tells me its not a carb issue.
I hope this helps
MrC.

[Flyingw]

MRCON. This problem isn't with any one single carb or machine, its a wide ranging problem effecting about 90% of all the QA series carbs out there. There are a few that don't have that problem whatsoever and that's what we are trying to figure out why most do but some don't.

[FoamingBadger]

That's a beautiful machine! I am having similar issues with my 86 250es but to a much smaller degree. My machine is very rideable just wants to cut out on full throttle when you punch it quickly. When I was a kid I used to drag race an 85 250es... (Haha if you can imagine such a thing) but it was dialed in very well and would pull sweet wheelies! Anyways I want my 86 running that well. I still have the old 85. She's roached real badly but mostly still there. I'm considering a rebuild on the 85 carb to see if it works better. Hope you figure yours out soon.

[ps2fixer]

Just had a chance to peek at a QA series carb. The top area of the plunger should be sealed well, the top plate has an o-ring so the only area I think it could leak is the shaft for pulling up the plunger. Maybe you could try to silicone the black plastic cover on to seal it to see if that's the area the leak is coming from? Same with the butterfly shaft, the capped side could possibly leak, maybe a little silicone around that too to test.

I'm wondering if it's just the passages in the carb getting a build up on the walls where you can't really clean it and that's restricting the fuel flow through the carb.

Are we sure the stumble is lean vs rich? In my mind it would most likely be lean but erosion is a thing too. Too bad the drill passages aren't easily accessible to clean up to validate they are free with no build up. I guess it would be possible to drill out the brass ball seal and run a numbered drill bit in, lot of work but could maybe make some sense of all of this.

[Flyingw]

So I took MMIguy's carb and put the slide in it from the Chinese knockoff and there was absolutely no change in the problem. I'm scratching my head guys. The butterfly shaft is not sealed absolutely so air being drawn from around the shaft causing the problem can be ruled out. The top cap does have a seal but that's to keep water and debris out of that area. That cavity is vented and that's where the jets get their air to feed air mixed fuel.

[Drakkar67]

I know this thread is a couple years back but I don't see anyone on the forum figuring out the bogging problem. I might be wrong but the hype focus on the carb may be the problem. Over the years everyone's machines most definitely has had a new airfilter put in them. We all know we like a nice flowing k&n but perhaps that's the underlying issue. To much air. The original probably didn't flow air as well as modern filters and how many of us soak it in gear oil before installing it. It would explain running lean and the need For the choke to get rid of the bog.once the rpms are up and running on the main jet I dont think the difference in airflow would matter. Just a thought.

[Dirtcrasher]

The easiest test anyone can do is remove the air box lid or add the air box lid to any motor, it helps tell you which way to go when combined with your jetting changes. Back in the day my 85 250SX was having some bogging/cutting out issues and I kept going after the carb. One day while it was idling I touched the harness and it sputtered, seems that the position the 85 mounts the CDI onto the battery box allowed the wires to flex with the rear suspension. It partially broke the wires inside the plastic CDI connector and once I replaced those pins, it ran great. Hondas typically have the same failures, and there aren't many, but some oddball issues do show up from time to time...

[ndavis1280]

Ok. So the answer is going to annoy you..probably. It doesn't bog wirh choke on and wide open throttle. SO...what does the choke do? Answer: restricts air flow to allow more fuel than air into the engine. You have a fuel/air mix problem.
How many fuel filters do you have on it? There should be 1 inside the tank for the petcock. PULL IT OUT AND CHECK IT. REPLACE the in-line fuel filter or remove it altogether. If there's a low speed jet..open it up a full turn. And only run CHEVRON Premium. Then also check timing.
I have a 85 250sx...never opened the carb up yet..not even once. Never even use the choke, Lol. I replaced the entire ignition system, fuel tank, petcock, fuel filter, starter solenoid, voltage Regulator, cdi box, and it runs great! Fast start, perfect idle, hauls ass, no bog. Good luck!

[350for350]

Except that these carbs use an enrichener instead of an actual choke. It's still called a choke even though it's technically wrong.