250sx carb issue, idles fine, dies if throttle is touched

[El Camexican]

well the pilot screw on an 85 sx is in front of the carb between it and the motor. a new one came in the kit. i think when i rebuilt it a second time i may have missed this step in the process. book says turn clockwise till it stops then, backing it out two turns. it also states in the manual that once the machine is warmed and good adjust idle speed, adjust pilot screw clockwise until the motor shuts off, then back out one full turn and readjust idle speed if needed.

If it still dies at two turns out from closed then try three and see if that changes anything. If is seems a little better, but still isn't right open the choke and see what that does. If it helps I'd buy the next two sizes up of pilot jets and start tuning. I assume its cold up there right? You may end up changing this again come summer.

[gladiator mice]

its suppose to be cold right now, but we have messed up weather. its been a maine machine its entire life. right now its 40 during the day and 25-30 at night, which is the only time i have a chance to work on it. i run my atc all seasons, my big red has never given me this much trouble. this sx on the other hand has been stubborn since i brought it home. im going to try the pilot screw tonight. so floats and pilot screw tonight. if its a no go im swapping the carb with my other sx and see what happens since they are both 85's

[Thorpe]

Here are two things I have learned about these carbs...

1)On my ES, rebuilt my carb, fired up great, top end ran like dookie... Tore the carb back apart and discovered that my new high speed jet (moose rebuild kit) was labeled the correct jet number, but the hole was much larger than suppose to be.

2)Factory floats are adjustable, just not the way you are thinking... Have a beer, once you are done, cleanly cut out a tiny square of aluminum from the can the size of that tiny square where your needle goes... You can shim floats back into spec this way.

I wasn't yelling at you in any previous posts, was just "excitedly" point out a major tuning issue... I have two of these motor'd trikes in my garage, I have been around these carbs enough to feel your irritation... We only know as much as you tell us, so details are important... As long as you are inside the carb, it would be a great time to fix the cold start issue the 85's are known for, by drilling your cold start jet to .080" too

[gladiator mice]

ok so heres what happened:

took the carb back off, checked the float and needle. works fine. adjusted the pilot screw one extra turn out. assembled intake on trike, checked air filter, closed air box. this time i left the air intake tube off just to see how it would react. started the trike up, ran it on choke to it was warm enough, shut choke off (BTW the choke works properly), idles fine, tried to gun it and it sputters and almost stalls just as i back off the throttle. i ease into it and its responding on the dot. i took it for a ride. at first just cruising around keeping steady rpm, got to the road and ed down (not from stand point), that trike ran like a raped ape, gunning it in turns and breaking loose the rear tires, easily pulling the front wheel off the ground. came back up to the garage let it idle back down, still getting the sputter/stalling when gunning it from idle position.

some where in this forum maybe, someone mentioned the kit i got may have sent the wrong jets. does any one know the stock jet size for the 85 250sx? if not ill pull my other one and check. usually theres a stamped number on the side of the jet.

[UPNATM]

Fellas, Im bringing up this old thread, because I am having the same issue with my SX. I have been through the carb 3 times, and it is clean. It is running lean, because when I choke it it runs fine, under a load, but without the choke, it stumbles, and falls on its face. Granted, it sat for many years, but I have changed, and cleaned everything I can think of, and am still having the problem. The only thing that I can think of that's different than before is that I changed out my stock Honda filter (it was wasted) for a Uni. Could I be getting to much flow out of the Uni compared to my OE filter causing the lean issue?

Thanks for the help.

[El Camexican]

Could I be getting to much flow out of the Uni compared to my OE filter causing the lean issue?

Highly unlikely unless you didn’t install it correctly and have air getting past it.

Did you remove and clean the pilot or slow jet? Do you have an air or fuel screw? (Air is before the slide fuel is past the slide closer to the engine) and how many turns out is it set at?

[UPNATM]

Highly unlikely unless you didn’t install it correctly and have air getting past it.

Did you remove and clean the pilot or slow jet? Do you have an air or fuel screw? (Air is before the slide fuel is past the slide closer to the engine) and how many turns out is it set at?

Yes, I went through the carb and cleaned and inspected everything.....twice. Its getting fuel, just not enough apparently when you stab the throttle. That's when it bogs, and stumbles.
I have also adjusted the idle air screw as well. Basically, I have been messing
with this problem for well over a week. Its got me baffled.

[UPNATM]

Oh ya, I forgot, I also moved the slider needle down a notch hoping to make the midrange throttle more rich. No change....

[UPNATM]

Well fellas, im still trying to figure this out. I had thought that when I had the supertrapp pipe installed many years ago that they may have rejetted the carb, to compensate. But, as it turns out it still had the stock 130 jet in it. So, I picked up a 132 1/2 jet, and installed it thinking that maybe after all these years, and fuel being different now a days compared to 20 + years ago, that jetting may have been my issue.
Nope, no change. Same lean bogging issue. Its so strange, I have done a search on the forum, as well as other ones, and it seams to be a somwhat common problem, but unfortunatly, all the threads juat dead end, with no fixed end result. So, im bumping this to the top again, in hopes of somebody who may have had the same issue, but was able to fix it, and get their trike running awesome again.
The only other thing I can think of to do is buy another carb, and try that.

[Dirtcrasher]

Whats it do if you take off the air box lid; Or have you already done so??

[UPNATM]

Whats it do if you take off the air box lid; Or have you already done so??

Thanks for the reply........ya, I ran it with the lid off, and also ran it with the gas cap fully unscrewed. No change
I also wrapped a rag around the air filter. My thinking being that it was getting to much air. No change when I did that either.

[Dirtcrasher]

When things run this poorly, the 1st thing is fuel flow. If the hose is off the carb and the petcock on, are you getting good clean flow?? We should all throw away the stock tank filter and run clear plastic inline filters.

If it flows to the carb, turn the petcock off and unscrew the drain screw on your fuel bowl to verify good fuel.

Also, again, if it runs that crappy, don't piss around with a jet just a hair larger, get a 140 and a 150 and read the plug.

Have you ruled out air leaks causing a lean condition? Spry some carb cleaner on the boots while it idles.

[UPNATM]

When things run this poorly, the 1st thing is fuel flow. If the hose is off the carb and the petcock on, are you getting good clean flow?? Yep, brand new petcock, and have great flow, and a clean petcock bowl.

If it flows to the carb, turn the petcock off and unscrew the drain screw on your fuel bowl to verify good fuel.I hadnt tried that, but just ran out and did. I got a steady flow from out of the drain tube.

Also, again, if it runs that crappy, don't piss around with a jet just a hair larger, get a 140 and a 150 and read the plug.Because it was running great when parked(rear diff was shot) I figured I would try going up gradually. I was thinking that jumping up to a 140 might be to much. I guess I will go down and pick up some bigger jets.

Have you ruled out air leaks causing a lean condition? Spry some carb cleaner on the boots while it idles.Tried that as well, no change to the idle.

Thanks for all your help!!

[Dirtcrasher]

Thanks for all your help!!

If it was perfect then with no changes, you seem to have a fuel starvation or some other issue: Electrical.

If you run with the A/B lid off well, it should need more fuel.
If you run with the A/B lid on better, it's too rich.

Plenty of times I have to jump 6 sizes. It must be a blockackage or something simple if it ran perfect before

Don't forget that the air screw goes (screw/spring/washer/o-ring) Make sure it's all there and no other air leaks. 1 1/2 turns out from lightly bottomed is a good start.

[barnett468]

Hello


You would have gotten more responses as a new thread

"It is running lean, because when I choke it it runs fine, under a load, but without the choke, it stumbles, and falls on its face."

Did it run fine before you parked it? If yes your gas is bad or idle circuit is plugged.

If it ran bad before your PILOT jet is too smal NOT the main based upon your description.