Hello!

I have 250 Rev 2007mod. and tryed everything, but motor runs lean. I raised fuel level, clean all jets trying everything with air screw, needle..

Can someone tell me the best sizes of jets for Mikuni carb.?

Thanks

Samo

If it just started running lean maybe you have an airleak. What throttle setting is it running lean at?

If it just started running lean maybe you have an airleak. What throttle setting is it running lean at?

When engine is hot and I am driving on steep hill with half throttle or more..

Gday, why do you think it is lean? - What symptoms are you experiencing? And have you looked at the spark plug?

Cheers,

Stork

When engine is hot and I am driving on steep hill with half throttle or more..

Is this somthing it just started doing or an ongoing issue?

Spark is ok. It runs lean from the first day I bought this bike. When I raised fuel level it was a bit better, but not as it should be.

I want to try with biger jets, they are not too expensive. Just need the right sizes.

Cheers

It sounds like you need a larger main jet since it's lean half throttle and up.

It sounds like you need a larger main jet since it's lean half throttle and up.

Do I need bigger needle also?

Is your air filter oiled properly ?

The Rev3's LOVE high octane gas. If you're running pump gas they'll not work anywhere near their potential. Typically the Mikunis came from the factory with 30 pilot jets and I think 140 mains. Usually around here we knock the pilot down to a 27.5 and depending on weather the main to a 135. If you can't get good fuel you might be able to retard the ignition a bit but the engine will lose some of its "pop".

Do I need bigger needle also?

Probobly not, but first you need to see whats currently in your carburator. Dan Williams disclosed the factory jetting. Open the carb and see which size jets are installed now. What altitude do you ride at?

I use always 100 or 98 octane gas.

Altitude I ride is around 500m.

Now I have 27.5 pilot jet and 145 main.

Thanks guys, I much appreciate your answers.

Samo

Samo, unless the carb is too rich from the factory you should be able to run the stock main and be ok.

Liviob, you mean 140 main?

I'll order 140 and 135 and try both.

I use always 100 or 98 octane gas.

Altitude I ride is around 500m.

Now I have 27.5 pilot jet and 145 main.

Thanks guys, I much appreciate your answers.

Samo

Samo, if you currently have a 145 main and you change to a #140 you will be leaner. If stock is a #140 and you are now richer on the main maybe you have another problem. Maybe the head has been shaved for more compression or the ignition is to far advanced and you are not running enough octain. What kind of symptom are you getting bthat makes you feel that the motor runs lean from half throttle up?

Edited February 16, 201016 yr by Liviob