[UnderWeight]

I just bought KLX250 which have a new motor that was extended to 300cc. After long ride on road, the motor stopped, on idle speed, idle speed become dramatic low. The mechanist tune the idle speed, but in the next long ride on road, it happened again.
Someone has an idea?

 

[ZX-2R]

YEP

See the same mechanic again...maybe the idle screw is just vibrating...are you riding it to hard, to easy...how does the plug look? Are you using fresh gas, and no additives? If you are just breakin git in it is recommended (see the mechanic first) that you add just a little oil to the gas tank to help lubricate the top end as it seats the rings. After you let it cool down does it start easy? If the motor gets warm and the rings are just tight enough it could be just the break-in...they ar etight enough when the motor gets warm to drag some...hence breaking-in, and it will cause the idle to be lower. Definately see the mechanic again...and don't forge to get back on the forum and let us know what you found out.

 

[UnderWeight]

KLX250 - carburetor - thanks

Thanks for your detailed answer.
I ride the motor off-road, but I don’t think it is too hard. I use fresh gas. For your recommendation I will check the plug.
What kind of oil to add the gas, if the problem cause because of the rings? The motor starts easy after it stopped, but if I don’t keep the gas, it will be off again.
Two questions:
Can it be because the tank cap is sealed and air cannot go through?
Does the following carburetor can fit this kind of motor (Mikuni TM36 with acceleration pump)?

 

[ZX-2R]

yes...

Use just a ounce of 2 stroke oil, Marvel Mystery oil, even a 10W40 oil would work. All you are trying to do is to lubricate the top end of your motor by adding some oil to the fuel. asyour rings are trying to seat it is rubbing against the cylinder walls, if the piston gets hot the rings swell with the piston causing greater friction an dmore pressure...that is why when it cools down it starts easy again. adding some oil to the gas tank for the next month or so won't hurt anything...in fact when rings get worn out or your top end needs rebuilt you are usually smoking pretty bad because you are using hte oil for lubrication, it is passing past the rings and you are burning it off the walls of the cylinder. SO you can add oil for the rest of your motors life and never hurt it...really! The old timers use to use Marvel Mystery oil to the gas and to thier oil all the time to keep things lubricated...it doesn't hurt...I don't know how it would work if you had injectors...It may not work, but a shot of diesel fuel would...diesel is oil based as well...it smokes and it makes your bike run hotter, but it does lubricate and clean out a system...
If your gas cap comes off in your hand try another one to see...you might ask someone else on how to check one, but the answer is yes.., if htere is a vacuum being created it causes the same symptoms...it will also run lean an dquit...

 

[hot_shoe_cv]

Re: KLX250 - carburetor - thanks

Thanks for your detailed answer.
I ride the motor off-road, but I don’t think it is too hard. I use fresh gas. For your recommendation I will check the plug.
What kind of oil to add the gas, if the problem cause because of the rings? The motor starts easy after it stopped, but if I don’t keep the gas, it will be off again.
Two questions:
Can it be because the tank cap is sealed and air cannot go through?
Does the following carburetor can fit this kind of motor (Mikuni TM36 with acceleration pump)?

I think you may have answered your own question about the gas cap ... it does require a vented cas cap. I had exactly the same problem once with my Yamaha Raptor quad when the vent tube on the cap became kinked and allowed no air into the tank.