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Re: slow moving Trac  MacDo-@aol.com
 Apr 09, 2001 18:29 PDT 
Sean, you say that your moped gets up to speed and then dies back to about 15
mph. A couple of things come to mind. It sounds like the moped is being
starved for fuel at higher RPM's. Check all the components that deliver fuel
to the engine.
Check to see how much fuel can be delivered to the carb. Disconnect the fuel
line from the carb and holding the open end in a small container, open the
fuel valve to see what the maximum fuel delivery to the carb is. You need to
make some judgment what is enough so keep in mind that a moped engine will
only use about 1/3 of a gallon per hour. If the fuel flow from the line is
that fast, then enough fuel is delivered to the carb. If the fuel flow seems
slow, find the restriction and clean it.
A fuel filter may be dirty and need replacement.
On many mopeds, there is a screen in the fuel valve that extends into the
fuel tank and you may need to remove the valve from the tank to clean the
screen. (Do not be tempted to reassemble without the cleaned screen back in
If you have ample fuel going to the carb then clean the carb with particular
attention the float valve. Use cleaner made for cleaning carb. Most
discount stores like K-MART will have it. Get the spray can and clean every
small hole you can find. IMPORTANT there are a couple of adjustment screws
on the carb that need to be removed on cleaned so you need to know how to
replace them. With a screwdriver turn the screws to tighten (clockwise) and
count the number of turns it takes to the nearest 1/4 of a turn. For example
the idle adjustment screw may take 1 3/4 turns to tighten. When you
reassemble the carb, turn this screw in all the way and then back it out the
1 3/4 turns to get it back exactly to where it was.
There is the possibility of an air leak into the air/fuel delivery, but you
did not mention what you may have removed and replaced. A poor seal at the
cylinder gasket could cause loss of crankcase pressure and cause the engine
to behave as you describe. There are also crankshaft seals that could be
leaking. Have you or the previous owner taken the cylinder off and not
replaced the gasket???
Check the fuel delivery stuff first and let us know how you make out. Keep
track of what you do so you don't keep going in circles trying the same stuff
over an over again.
I hope this helps.
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