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04 YZ250F Jetting issues

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The past year, my bike has been developing some serious backfire on decel. Deciding to work on my jetting, I purchased a JD kit for the bike. I went with the suggested:

185 main

Blue needle 5 groove down

1 3/4 turns out on fuel screw (also bought a zip-ty fuel screw)

To do all the work right, took entire carb out of bike and proceeded to do the above. Squirted myself good by turning throttle pulley and looking at the engine side of carb. Oops! I also installed a new cable for the hotstart as the cable was seized, not the plunger.

Once done and buttoned back up, the bike would not start at all. I got 2 revs that lasted about 1/2 second or so and some backfiring. Took it all apart, looked at things, installed a new plug. Have good spark as well, made sure all electrical connections were firmly seated. Still no fire.

Ok, start working backwards then. Took carb out, installed the stock MJ, a 180. This time I notice no fuel squirting out of carb output side. Hmmm I thought. Still no go. Reinstalled the stock needle, clip in 3rd position down. Fuel screw still the same. So in theory, I should be back at stock settings before I started all this work. STILL no starting.

Now I am thinking, go back to stock fuel screw? Carefully, with carb on bike, I removed fuel screw slowly so I do not loose o-ring and minuscule washer. Keep in mind, I left the petcock ON. Shouldn't gas have come out of the fuel screw opening without any fuel screw in? None did on my bike. When I put the stock main jet in, fuel did come out of the 17mm opening to access this, so that area is getting gas?

By the way, I did check the plug when back to stock setting to see what it looked like/smelled like. Looked nice and clean, no noticable residue.

Any ideas on this? Did some dirt get in the carb, blocking something? I know there is always residual gas in carb so turning the throttle pulley will result in few squirts. Would a new hot start affect this? I never ever used it, hence the cable seizing.

Thanks all for the help. Will be checking back tonight and first thing in the AM as I'd like to go riding Sunday.


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Sounds like ignition to me. Check for a spark with the spark plug removed. Also you didn't mention what you are running for the pilot Jet, I assume a 42?

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