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Low-speed carb problem

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I am experiencing idle to low speed carb problems. After the bike warms up I still can't "blip" the throttle or the engine dies like its getting too big of a shot of gas. Also, the engine runs rough just off idle. I've cleaned inside the accelerator pump and checked for other obvious problems like air leaks but with no luck.

My bike is modified as follows based on Clark's previously posted tech advice:

-99 WR400 with YZ timing

-YZ DVP Needle in 4th clip position

-#48 pilot jet

-#180 main jet

-airbox top removed

-octopus removed with all hose barbs capped off

-#100 pilot air jet

-TPS rotated fully clockwise

-stock YZ pipe with aftermarket oval disc set (12 discs)

-FMF oversized headpipe

Any help is greatly appreciated.


Jeff (jeffdogge@yahoo.com)

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Where is your pilot screw at? (turns out) Should be about 1-1 1/2 turns.

Did you check to see that the pump is squirting when the throttle is opened? Pull back the air boot to see.

Was it running good with this setup before or is this a new attempt at better performance?

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Hello James.

Pilot screw is at 1-1/4 turns out. I am aware that adjusting the screw can help at times, but it doesn't in this case.

I have NOT checked to see that the accelerator pump is squirting fuel when the throttle is opened. I'll try this next and see what happens.

It was running good with this setup before, even though I had an FMF Powercore 4 pipe mounted and didn't have the right jets in place. Now I'm running a stock YZ pipe with a 12 disc set and fresh packing. There shouldn't be that drastic of a difference. I'm suspecting that something has simply gotten out of adjustment with the carb or my TPS/accelerator pump is misadjusted or even bad. I dunno.

Thanks for the help thus far...


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