I have a Honda TRX300FW that will suddenly not run properly. I got it and it was running perfect. I did a full service on the quad( oil change w/filter, diff lube change front & rear, transfer case lube change, new air filter, new spark plug,& fresh gasoline.

After the service it ran perfect for 2 days, then the trouble started.

It will start at a touch of the starter button and idle for days.

After letting it warm up, as soon as you try to give it throttle it will stutter and sometimes die or stutter and then pick up the rpms but it sounds like it is running against the rev limiter. It is blowing black smoke out of the exhaust.

If it gets past the mid rpm range without stalling it will run in the high rpm range but the rpms pulse up and down. At this point the smoke goes away but the engine will not run at a consistent rpm.

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So far I have done the following:

1) pulled the carb, disassembled and cleaned all the parts/housings/float bowl/fuel lines, and reassembled the carb.........3 times...put the carb back on the quad and no change in performance.

2) Checked all around the carb with the quad running for any vacuum leaks........there are none....

3) Adjusted the idle screw on the bottom of the carb both out and in.......no change in performance..(presently set at 2 turns out)

4) Replaced the CDI with a new one from Honda.........$150.00 later....no change in performance..
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Does anyone have any ideas about where to look next????