hello to all. Did anybody here ever had a problem with engine just shutting down with no apparent problem?
i bought a 07' KLX250s, looks like new, has 700 miles on it, after it starts it will not hold RPM only if the choke was on, and after it warms up it was still not able to stay on and just shut down with no reason.
i took the carb off and cleaned it, didn't solve the problem, took the carb to a bike shop, he cleaned and tuned it and even added a missing part and even that didn't solve the problem.
the bike starts cold no problem, holds for a few seconds and just shut off, if I start riding it, it will
sound great for a few seconds and then it will again, shut of with no reason. It sounds really good cold or warm, I don't think it's the carb anymore. Any sujestions?

 

Will it re crank after it dies?

If it will run with the choke on then your problem is fuel delivery plain and simple, either junk in the carb that you do haven't gotten or you may have a large air leak somewhere, check the rubber boots for cracks. While running spray some propane or starting fluid around the boots, if your rpm changes you have an air leak

 

Make sure the carb is getting gas, you could have plugged lines, junk in your filter, or even a vacuum problem stopping fuel from flowing to the carb. It's all down to if it runs with the choke.... If it does then you have a fuel/air problem.

If it really does just randomly die, then IU would look at the CDI box, they are notorious for working when cold and then not when hot, we need more details to help you

 

Sounds like the classic case of a clogged idle circuit. Will start and run on choke - an enrichener circuit on the Mikuni - but will not run when the choke is closed - no longer feeding gas and air. I'm betting on that, the idle mix circuit is clogged. This happens when bikes sit with gas in the float bowl with the fuel shut off. The liquid evaporates leaving a dry residue. When fresh gas hits it the residue either flakes off or turns to goo and gets sucked into the tiny pilot circuit, clogging things up in hard to reach spaces. Saw it scores of times in the years I worked in the bike shop. It was nearly a yearly ritual for some riders to have to have the carbs cleaned. Personally I never turn off the gas so it always has liquid in the carb and as long as the float needle does its job there is no overflow - and yes the float needle always has worked.

How did the bike shop clean it? If there is gunk in the very small idle circuit it will resist all the wire probing and spray cleaners. The carb body will need to be cleaned using either a carb washer that quite literally sloshes the part and fluid around for several hours, or an ultrasonic cleaner that does the job with ultrasonic waves in the fluid.

Those machines can get the goo or crud build up to break down and rinse away without damage. It may take an overnight cleaning. This is what I observed when working in a bike shop years back. If they didn't wash the bodies long enough it wouldn't clean out.

Wild part was when they had a less eco-friendly cleaner - one that required rubber gloves or fast rinsing - the carbs would clean out fast. But you dare not leave them in the cleaner too long. Now with the eco-friendly stuff it won't burn your skin or erode the carb bodies, but it sometimes takes a lot longer to work.

Check with a car parts store that does engine parts cleaning, they may be able to help best.

 

Thank you all for the quick respond, I took it to a bike shop for cleaning, and told them all the symptoms I'm having, I assume the soaked it in a bath as far as I understood. The bike runs with the choke on but will eventually stall with the choke on too after a few seconds and in gear. I tried to let it sit for a little bit, it started right away, and even without touching the throttle it will just die after a few seconds and sometimes it will die right away and it will take a few more attempts to actually start again.
I am about to buy a new spark plug, that's my next step. I rev'd it up to about 3000rpm without the choke and it was not running smooth, and after a few seconds, again, it just dies.
I appreciate all of your responses guys
thank you

 

There is a tiny fuel filter in the fuel inlet of the carb. I found mine was red up in the fuel line. It would be a good idea to check your fuel line for any obstructions. Also, check your peacock for proper flow. It may be fuel starvation.

 

Well, good news everyone, she started and running with a new spark plug, after a few minutes around the block she kept running smooth also in idle. The only thing that I noticed is that after a couple minutes at idle the RPM raised a little by itself, might be just the carb still cleaning residue or maybe an intake leak? Any suggestions?

 

Jetting? KLX300 bits or Dyno Jet if not already done. I have the KLX300 stuff in mine, as does my brother and works fine. In the KLX250 cheap hop ups in my signature. Or Dyno Jet and look up KLXter's work in the forum. Either is gonna be better than anything. Start and idle better and easier.