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rickybobby2189

99 Yz400F Jetting

4 posts in this topic

I am in the process of getting the kinks worked out of my bike.I have searched alot of threads and have not found exactly what I am after. I have a completely stock yz400.Original right down to the air filter. The plastic cone piece behind the air filter is missing and the air box lid is off.Will this have an effect on the way it runs? My problem is I cant seem to get a steady idle and backfires on decel. I have searched all over it for any air leaks and have found none. It would idle for about 30 seconds and then fall down to where it wouldn't idle and then die. Now I have got it to where it will idle (kindly high) and in between gears and coming to a stop it keeps pulling. I am getting frustrated with it and need some help. Is this a jetting problem? I dont know if it effects it with the air box lid being missing and the plastic cone thats suppose to be behind the filter. I have found in threads that some people solved their problem with little as a bigger pilot jet.Is this something that would be solved with a larger one? I use this bike on the track so I cant deal with the hanging idle and then stalling out on my races,I need it to run tip top. Can someone with some know how please help me.

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My problem is I cant seem to get a steady idle and backfires on decel. I have searched all over it for any air leaks and have found none. It would idle for about 30 seconds and then fall down to where it wouldn't idle and then die. Now I have got it to where it will idle (kindly high) and in between gears and coming to a stop it keeps pulling.

These are symptoms of a lean idle mixture. Read:

http://www.thumpertalk.com/forum/showthread.php?t=327405

...and:

http://www.thumperfaq.com/jetting.htm#PJ

You should also check to be sure you don't have a leaking hot start, a tight valve or two, particularly the intakes, or a damaged vacuum release plate on the engine side of the slide. If you don't get some reasonable result from these things, the carb may simply be bad.

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I am glad you said that,The tight valve part...Mine are really tight.You replied on my other thread about the valves and I should have my new valve seals and shim kit in the next few days..Will a tight valve cause this such thing? I am hoping you will say Yes lol...I will richen up the pilot after I get everything back together and new seals put in it.

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..Will a tight valve cause this such thing?

No, I just say stuff like that for fun. :smirk:

Yes, tight intakes will cause a lean condition by reducing the strength of the intake vacuum signal.

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