04' YZF 250 popping

I have read other members problems with jetting, but still I am not clear on what I should try for my problem.

On deceleration my bike pops a lot, I am at 5000+ altitude.

I have a 178 main and 42 pilot, the needle is in the stock position and the fuel screw is at 1 1/2. I tried to bump the pilot to a 45, but I could not start it afterwards. I was thinking of richening the needle by one clip, do you think this will help.

Thanks ahead of time. :):D

Have you tried turning the fuel screw out? Maybe 2 turns.

I have the same problems, but at a much lower altitude. I am riding this weekend with a Yamaha dealer and I am going to ask him about it. I will let you know what he says.

I've been out as far a 1 3/4 turns on the fuel screw, but I have been told that you generally should run the fuel screw from about 1 1/2 to 1 3/4, so I was trying to jet my bike in that range. Is there any truth in that? Even if I backed the FS out to 2 I'm pretty sure the popping will continue. The temp. was about 50 degrees. :)


Raising the needle will help if your popping some where between 1/4 & 3/4 throttle position. If you're poppin above 3/4 throttle go bigger on the main jet.

The '04 YZ250F will be more likely to have popping on deceleration than previous year models because of the jetting chages. A #42 pilot jet will help, but the fuel screw will need to be turned further inwards from your description and considering altitude.



Well, I asked my buddy who owns Beach Yamaha about the popping and he said it is normal. It just means it is running a little bit "lean"...... BUT if you like how the bike responds to the throttle, don't change anything. The popping won't hurt the bike at all. I hope this helps. Good Luck.

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