samo Posted February 11, 2010 Report Share Posted February 11, 2010 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 Quote Link to comment Share on other sites More sharing options...
liviob Posted February 11, 2010 Report Share Posted February 11, 2010 If it just started running lean maybe you have an airleak. What throttle setting is it running lean at? Quote Link to comment Share on other sites More sharing options...
samo Posted February 11, 2010 Author Report Share Posted February 11, 2010 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.. Quote Link to comment Share on other sites More sharing options...
stork955 Posted February 11, 2010 Report Share Posted February 11, 2010 Gday, why do you think it is lean? - What symptoms are you experiencing? And have you looked at the spark plug? Cheers, Stork Quote Link to comment Share on other sites More sharing options...
liviob Posted February 12, 2010 Report Share Posted February 12, 2010 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? Quote Link to comment Share on other sites More sharing options...
samo Posted February 12, 2010 Author Report Share Posted February 12, 2010 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 Quote Link to comment Share on other sites More sharing options...
liviob Posted February 12, 2010 Report Share Posted February 12, 2010 It sounds like you need a larger main jet since it's lean half throttle and up. Quote Link to comment Share on other sites More sharing options...
samo Posted February 12, 2010 Author Report Share Posted February 12, 2010 It sounds like you need a larger main jet since it's lean half throttle and up. Do I need bigger needle also? Quote Link to comment Share on other sites More sharing options...
b40rt Posted February 12, 2010 Report Share Posted February 12, 2010 Is your air filter oiled properly ? Quote Link to comment Share on other sites More sharing options...
dan williams Posted February 12, 2010 Report Share Posted February 12, 2010 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". Quote Link to comment Share on other sites More sharing options...
liviob Posted February 12, 2010 Report Share Posted February 12, 2010 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? Quote Link to comment Share on other sites More sharing options...
samo Posted February 13, 2010 Author Report Share Posted February 13, 2010 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 Quote Link to comment Share on other sites More sharing options...
liviob Posted February 14, 2010 Report Share Posted February 14, 2010 Samo, unless the carb is too rich from the factory you should be able to run the stock main and be ok. Quote Link to comment Share on other sites More sharing options...
samo Posted February 15, 2010 Author Report Share Posted February 15, 2010 Liviob, you mean 140 main? I'll order 140 and 135 and try both. Quote Link to comment Share on other sites More sharing options...
liviob Posted February 16, 2010 Report Share Posted February 16, 2010 (edited) 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, 2010 by Liviob Quote Link to comment Share on other sites More sharing options...
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