YZ 250 F jetting

on my 04 250F I worked on the accelerator pump(as seen in the recent Transworld issue) and now my bike is popping real bad, could i just adjust the air screw? it is 38 degrees. I dont know that much about jetting so I really didnt know what was up. could anyone tell me what I need to do

Nice pic :D

Nobody else is answering so I'll try. I think your bike has a fuel screw not a air screw. Hey, I got corrected on this earlier too. If it's on the engine side of the carb it's a fuel screw. Aircleaner side a air screw.

The cold denser air makes it run leaner so you would need to richen up any "circuit" that is poppin. This explains it better than I can: http://www.motocross.com/motoprof/pdffiles/carb101.pdf

Also, if it doesn't rev quick as normal you probably made the affected circuit too fat. Good luck! :)

Try turning the FUEL SCREW outwards to richen the low speed jetting for cold temperatures. See manual. Turn it in 1/4 turn increments and keep track of where it was set initially.

If you removed the slide at any point, make sure you replaced the square end down on the slide plate. This plate must be installed with the square end down or excessive popping and poor running will occur.


Thanks JD I did as you said and it runs like a champ now. Also I changed to a Iridium spark plug, and am gettin noticable results. it seems to pull alot harder throught the powerband. I highly reccomend getting one to all who havent already. :)

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