Poor running tips? By looker (Read 751 times)

[looker]

Hi guys,
mainly a question for carburettors, should we come across symptoms of poor running.
Things that I can think of (apart from hard to start and poor idle) are:
stuttering when revving from idle,
symptoms of a too large main jet (running rich),
symptoms of a too small main jet (running lean),
symptoms of a vac/air leak

Pulling the plug to check it's condition is a common diagnostic, but was just wondering if anyone has had any of the above problems and what it turned out to be.

My scoot runs fine, but thought it would be good to know about these things incase they happen so it could help with what to look for when fixing it.

Mike

[sprocket]

You missed the obvious as so many people do.. the throttle needle. This runs from the diaphragm to the main jet and controls the entire carb power curve...It is totally adjustable and will often solve all the problems you mention one way or another.

Everyone throws on a foam filter and few know to oil them. Then they start swapping out jets for a few months trying to get the engine to run right...

The idle jet should probably never be changed and the main jet should only be changed if the adjustment of the throttle needle, does not correct the situation.

Every day I hear of people going from a 108 main jet to a 120 or something. Just stupid!

The rule of thumb is go up two jet numbers for each change you make to the engine. So you could consider going from 108 to 110 if you changed from a paper filter to foam, and then form 110 to 112 if you put on a free flow exhaust.

But all this could be easily accomplished in two minutes with the throttle needle adjustment.

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