QuestionBought used. thought it had a fuel problem. seemed like it was getting no fuel. Cleaned out Carb. Piston/rings have been changed. Still no power, will hardly stay running. Could it be a compression problem?
AnswerHello,
The problem could be low compression
but there are many other possibilities.
First thing I would do is to check
all the basic tune up items.
Check spark plug, air filter, fuel supply
from tank, air leaks around carb
or intake, and very important to
the compression is the valve clearance
settings.
Do a quick check with the engine on compression stroke and
the piston at the top. The valves
or rocker arms need enough clearance to be perceptible
by feel.
Check if the throttle is opening properly.
Check the spark plug color for clues
on what is happening inside the cylinder
during combustion.
http://verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm
If you find the spark plug very sooty then it
is getting too much fuel, maybe the choke
or enrichener is stuck on.
The fuel cap or tank air vent can plug and
prevent fuel flow to the carb.
The exhaust port or pipe could be plugged.
You will have to eliminate one thing at a time
to find the problem.
The bowl on the carb should be nearly
full of fuel when the float is set properly.
Make sure the fuel is fresh and no moisture
in it.
Carb jets have to be cleaned
physically as the fuel can gel and harden in them.
The idle and main jet in the center have to
be very clean.
No power could also be something as extreme
as a damaged piston or cylinder wall
but a compression test should show that.
Most modern engines have over 150 psi compression.
Check compression with the ignition off and throttle held wide open
to allow air into the engine.
There may be a slight chance of a faulty
ignition component but not likely
if the spark will jump a 5-6 mm (3/16") gap.
Let me know if you have any new info.
Luck!
Wayne S
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