Honda 250sx still bogging

[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!