What else can cause four stroking or rich conditions?

Jake Pearson /

I have an urban express... it pulls great and runs fine until the very top of the throttle, and then it starts four stroking.

The odd thing is, the plug looks great and tan. I'm running a stock jet and even with no air filter and the mixture screw as lean as it will go (almost), it seems to run exactly the same and four stroke at exactly the same point in the throttle as when I have the filter on and the screw as rich as it will go.

Is there something else that can cause four stroking-like sounds, or is there something that can cause it to run so rich that a lack of filter and lean screw wouldn't make much of a difference?

Thank you everyone

Re: What else can cause four stroking or rich conditions?

Emil Kniemel /

throw a pipe on it.

Re: What else can cause four stroking or rich conditions?

♣Slew Foot♣ /

bigger fuelines? gas cap vent. stupid stuff first, filters clean?

Re: What else can cause four stroking or rich conditions?

♣Slew Foot♣ /

i didn't notice the rich condition comment.

reset your points to factory spec. it may be off a hair, regap the points. check the state of your exhaust. is it clogged?

Re: What else can cause four stroking or rich conditions?

Jake Pearson /

My pipe is clean, my ports are clean. I will reset the timing, I didn't know timing could cause four stroking. Thanks! I'll see if that works

Re: What else can cause four stroking or rich conditions?

♣Slew Foot♣ /

if you are retarded it can give a low end boost and rich conditions, advanced a top end boost and a little lean, if the gap is too much it can miss at high speed.

Re: What else can cause four stroking or rich conditions?

The pilot "mixture screw" only affects the engine at idle and just off idle.

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