99 YZF400 wont idle

Ok I have a 99 YZF400. Iv been through the carb like 4 times cleaning it and cant find anything. Iv tried everything I know. It will start right up with the choke on and idle fine but the second I push the choke in it will die. Sometimes it will idle for a few socond but then die. If I keep snaping the throttle then push in the choke It will stay running fine and I can fly around no problem and do catwalks for ever but if I let off and pull in the clutch it just dies. Iv been messing with it because it pops a little more than I think it should when i let off the throttle like a lean pop but need to get it to Idle. Any ideas would be nice.

check your idle speed air screw play with it a little bit if that doesn't work try messing with you fuel mixture screw. If the carb is clean and the air filter is clean this should resolve the problem. unless your timing is off.

If your air filter is really clogged up it will be hard for your bike to breathe at low rpms four strokes don't create the same vacuum that two strokes do so a dirty filter can be a big factor

Where is the fuel mixture screw. I only know the idle air screw. Ill double check the timing but I dont think its that. Last time I had the timming off it wouldnt ever even start.

I suggest the following:

Get a manual. Go to the technical FAQ's at the top of this forum and download the manual.

Check your valve clearances and adjust as may be required.

Check the intake manifold for any cracks/leaks as these may cause a lean condition.

Check the technical FAQ's for carburettor settings for the YZ400f. Mine runs fine on standard jetting and around 1 and half turns out on the fuel screw (the one at the bottom of the carburettor towards the front centre). The settings are dependent upon where you are running (altitude etc) however. In my case I am at low altitude and hot desert conditions.

Persist with the tuning because once it is set up right it will start and idle reliably. Don't resort to any after market changes as generally they are not required.

Good luck.

Wow that might help alot. I always thought the black knob was the idle adjustment then everyone was telling me thats the fuel screw and thats what Iv been asjusting but ya ok now Ill see if it will idle.

Ok I tried adjusting the fuel screw but that isnt helping at all. I double checked the valves and timing and all is good. So I have no Idea. I think Im guna have to break down and bring it somewhere.

If everything else is correct, jetting, timing, air filter, etc the airscrew on the bottom of the carb should be at about 3 turns. the black knob will then bring your idle up or down. Make sure there are no leaks anywhere in the exhaust or around the carb/intake/airbox/hot start knob. popping on decel is usually form a lean condition or leak. I had a 99 400f and fought the jetting constantly. A JD jet kit helped tremendously. A auto decompression cam or hot cam exhaust cam will help starting 100%!

Well it idles now all I had to do was pull the stupid apark arestor plate out of the end of the exhaust and one kick and now it idles. But I still have to mess with the jetting but Its more like a back fire that a pop cuz its really really loud.

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