KX250 wont rev?? Unless choke is ON.

My buddies 2002 kx250 has a problem.

We were riding down a road when the motor suddenly bogged down and now it wont rev.

The bike will Idle just fine, but if u chop the throttle, as soon as it starts to rev it just bogs out, and u can let off and it will idle again. If the choke is on, the motor will rev freely and behave normal, as soon as choke is closed it bogs again.

Sure seems to me like a carb issue.. The spark plug is new less than 2 hours on in it. We tore the carb out and checked the jets, they all seem clean, we blasted everything out with carb cleaner. While we had the carb off we pulled the reed cage, everything looks copasetic in that dept.

Really at a loss of what to look for.. I am convinced its the carb, seems like a MJ issue??

Only other thought would be powervalve.. But whats really confusing me and got me convinced its the carb is because it will rev hard if the choke is on..

Its lean. The choke cuts off air thus allowing it to rev. Fatten your main and needle

Well I wouldnt fatten anything if this is something that happened all of a sudden. It sounds like your pilot jet is plugged up. Maybe you pulled some debris into the carb. Take the carb apart, clean it, if the pilot jet is plugged replace it, they are very difficult to clean, Check the main jet also.

Ya it happened all of a sudden... Dude bought the bike a few months ago and it has been running just fine.. We had even been riding for about an hour or so that day before it bogged.. He was riding behind me crusing on a road when he said it lost all power n bogged.

I looked at the pilot jet, it doesnt look clogged to me...The outside doesnt have any gummed up residue and I can see through it if i hold it up to the light.

The jets honestly look clean but maybe there is something we are missing..

i just realized that I dont remember seeing a clip on the needle but i will have to call and ask him.. Would that do it? Could the clip come off the needle and then make the carb malfunction?

Absolutely, if the clip is gone it would lean out the mid major! How it would be gone is beyond me but who knows, Clean the pilot and reinstall. Make sure your airscrew didnt fall out. Clean main also. Being as it runs good with choke on means it is definitely lean. has to be a jet/carb issue.

Its lean. The choke cuts off air thus allowing it to rev. Fatten your main and needle

Been a while since I've seen a two stroke choke that restricts airflow, unless it's a 50cc. Most of them are "fuel enricher" circuits. Providing extra fuel.

So yeah, anyway, it's lean! Clogged pilot most likely.

I'm gonna say partially seized main bearing. :smirk:

I'll say look at the power jet that supplies fuel enrichment at different loads and rpm's,

An electronic solenoid controls the timing of the power jet. usually the solenoid remains retracted / open if no current available as a safe guard to stop any damage to the engine.

Clogged jet or the solenoid's jammed on / closing off fuel flow...... Just another item to check... Good luck...

Been a while since I've seen a two stroke choke that restricts airflow, unless it's a 50cc. Most of them are "fuel enricher" circuits. Providing extra fuel.

So yeah, anyway, it's lean! Clogged pilot most likely.

Thats what I mean't, enrich airflow by whatever means I guess. Guess it doesn't block off air unless its my 50cc chinese scooter carb lol

Man I really hope you guys can figure this out because my bike is doing the exact same thing. Exactly the same. Any ideas on how to check the fuel cut solenoid?

Well I can promise you this its not a partially seized main bearing and the bike does not have any kind of solenoid in the fuel system.

One other thing to look at. I have heard, but have not had any personal experience that a broken reed could cause this symptom also. Something to look at.

Well I can promise you this its not a partially seized main bearing and the bike does not have any kind of solenoid in the fuel system.

Dude it a 02 kx 250, think again about your statement ^^^ :smirk:

Edited by hsv434
Man I really hope you guys can figure this out because my bike is doing the exact same thing. Exactly the same. Any ideas on how to check the fuel cut solenoid?

factory as a fail safe feature (remains on richening the A/F) if there's any CDI harness/wiring issues or if the soleniod bad. there's a little needle on the end of the solenoid that's retracted leaving the power jet open. Check the power jet by removing the fuel bowl and spray parts cleaner into it. you can see the power jet it's located on the carb/bowl mating surface. the sevice manual has the electrical test procedure to test the solenoid...good luck with your bike:ride:

factory as a fail safe feature (remains on richening the A/F) if there's any CDI harness/wiring issues or if the soleniod bad. there's a little needle on the end of the solenoid that's retracted leaving the power jet open. Check the power jet by removing the fuel bowl and spray parts cleaner into it. you can see the power jet it's located on the carb/bowl mating surface. the sevice manual has the electrical test procedure to test the solenoid...good luck with your bike:ride:

U realize we are talking about a 2002 kx250 2-stroke right? I had no idea that there is a soleniod like this on these bikes (but in my defense i havent owned one.) Do all the bikes have something like this?

update: No news he hasnt been able to look at it yet. I told him these suggestions/reasons.. Which mimicked mine because of the choke situation..

I told him to replace the jets..we'll see

Wow! My bad. How the heck I didnt see that I dont know. Had 85 or 100 on the brain. Still would not be a main bearing. Thats what happens when I post at 1:30 in the morning.

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