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

[gladiator mice]

checked the exhaust last night. clean and free flowing as could be. no restrictions. checked the air box intake tube and inside the frame, clean as can be. put the trike back together, and gave it a shot. still can get it to start and idle fine. choke cable and and choke plunger work correctly with no damage to small needle. a quick push on the thumb throttle and it comes close to stalling. ease into it and i can hit high rpm, release throttle and it drops back to idle. every time i gun it it stalls or comes close to it just as i back off the throttle. shut it down and tore it apart. took the carb off, disassembled it cleaned it with carb cleaner and the air hose. took all the jets out and cleaned each one and the air ports and gas ports in the carb. reassembled the entire carb and trike. emptied the tank, fresh gas, cleaned the spark plug (to help tell me what new stuff is on it), used the air filter out of the big red, started it up, idled fine, let it get warmed up some, gave it some throttle and i get the same response from the trike as i did in the beginning of this thread. might still having trouble going from slow jet to main jet. also the spark plug tip was black but not wet. the main throttle needle IS set to the correct notch and i used a manual to rebuild the carb.

[Flyingw]

For the cost of shipping, how about I send you one of my rebuilt and tested carbs for troubleshooting. If with my carb, it would eliminate every other possible cause. Just a suggestion.

[Thorpe]

Really, then why did you say you DIDN'T install your AIRBOX... Did I offend you?? Try a rebuild kit in the carb rather than cleaning it...

[Flyingw]

Im with Thorpe, before going any further, install the airbox. These carbs are tuned for the airbox.

[Flyingw]

Also, start it up with the airbox off and partially restrict air flow by placing your hand over about 3/4 of the carb opening. Hit the gas and see if it makes a differance.

[El Camexican]

I did put the air box back in and assembled the trike. DIDNT MAKE A DIFFERENCE!!!

Also theres no reason to cap me, or anyone FYI.

Chill out Man. What Thorpe posted is 100% bang on the money advice and correct me if I missed it, but you never went on to say that you put the air box back on in your posts. I suspect his “CAPS” are to get your attention, not to disrespect you, if he wanted to do that he’d likely have asked you about how a jet fell out of your; and I quote: “everything i took off went back on, all replaced parts were replaced properly.”Carb. People that beak-off at others who are offering FREE advice end up getting ignored and with all due respect it sounds like you could use all the help you can get right now. Peace.

[gladiator mice]

when i refer to rebuilding a carb, i dont go the cheap way and spray and air it out. i already bought a rebuild kit from jets r us and in the kit comes new jets, gaskets, and needles. the carb was cleaned and assembled and installed "with the air box in and tube connected to the frame". still got the issues of gunning it. i now suspect the plastic floats are the issue as if the tab that holds the needle (with the rubber tip) is not working correctly. it lets enough gas, steady flow, to keep the trike at idle but might be screwing up. ill switch it with my other sx and see what happens for shits and giggles.

also for those still rattling on about the caps issue. i was not offended, i read each response no matter what and take the advice with honesty of one person helping another person out. but capitalizing a sentence is not going to make my problem solved or anyones problem. when most people see capitalized words or sentences we do think the person is yelling. theres no reason to yell.

[El Camexican]

i now suspect the plastic floats are the issue as if the tab that holds the needle (with the rubber tip) is not working correctly.

YOU NEED TO (just kidding) take a good look at the float height. I didn't see where you mention them before. If they were stuck to the bowl when you pulled it off the carb body the tab may have been bent and that would cause the float to close before enough fuel gets into the bowl. Float height is always important and even critical on some models. Do you know how to properly set float heights? If not, Google it, there are some good reads, I think JetsRus may even have a link. You mention that the needle (rubber tipped thing) is not working properly. Can you explain why you think that? Its only job is to seal on the seat and stop fuel flow when the floats reach a set height. It will appear loose exept when it is closed, but as long as it moves freely with the floats and doesn't leak it is working.

This very well may be your last remaining problem as too little fuel in the bowl can cause the engine to die out under throttle.

[gladiator mice]

YOU NEED TO (just kidding) take a good look at the float height. I didn't see where you mention them before. If they were stuck to the bowl when you pulled it off the carb body the tab may have been bent and that would cause the float to close before enough fuel gets into the bowl. Float height is always important and even critical on some models. Do you know how to properly set float heights? If not, Google it, there are some good reads, I think JetsRus may even have a link. You mention that the needle (rubber tipped thing) is not working properly. Can you explain why you think that? Its only job is to seal on the seat and stop fuel flow when the floats reach a set height. It will appear loose exept when it is closed, but as long as it moves freely with the floats and doesn't leak it is working.

This very well may be your last remaining problem as too little fuel in the bowl can cause the engine to die out under throttle.

the needle and rubber is working, i mixed my words up, i was referring to what you stated about the float being bent and stopping the fuel too soon. a friend out in the shop said the same thing you just wrote.

[El Camexican]

a friend out in the shop said the same thing you just wrote.

Sounds like your friend is a smart guy

[gladiator mice]

Sounds like your friend is a smart guy

he knows his snowmobiles and atvs. hes usually the first person i go to, he doesnt trust mechanics touching his stuff or leaving it alone with them

[Flyingw]

Remember, the float adj on the ES and SX carbs are fixed. No adjustment of the float is possible. If you suspect the float height is incorrect, replace it.

[just ben]

I had the same symtoms but on a different machine. It came down to getting the air screw dialed in. at the base line setting it ran just as you are saying yours is. I don't remember exactly but I think I had to open it another 2 turns or so.

[El Camexican]

Good points by Ben and Flyingw. I don't know your machine, but if the float is fixed then Ben has pointed you in the right direction. Does it have an air screw, or a fuel screw? "Air" is typically on the air-box side of the carb and “Fuel” is on the engine side. If it's dying out you are likely lean, so you would close an air screw, or open a fuel screw to correct this.

If this turns out to be the fix you may want to consider buying a different pilot, or slow jet if the best setting ends up being more than a full turn away from the recommended base setting. It won't hurt to just run it like it is at say 3 turns out, or only 1/4 turn open, but it limits your ability to tune if temperatures change or you ride at different altitudes. It’s always better to be spot with your jets so that the other fuel circuits can transition as smoothly as possible.

As far as fine tuning goes I like to get the engine to operating temp and whack the throttle open from an idle (in neutral) to see if it the revs come up cleanly. If it dies, or stumbles like it is about to die its likely lean, and if it burbles and struggles to come up its rich. If it runs better on the choke that’s a sure sign that it is running lean. Anyway, I’m getting ahead of things here, get in running and then you can enjoy fine tuning it with your buddy.

[gladiator mice]

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.