QuestionNo. 1 cylinder spark plugs spark when held against head but when fitted No. 1 ex. pipe doesn't get very hot (not firing on No. 1) and when I take off No. 1 plug lead there is no difference in engine revs. Also you can smell unburnt petrol out of the ex. pipe
AnswerHello Ian,
You will have to check a few things
carefully to determine the problem with
the number one cylinder.
The first thing is checking the
spark plug condition and color.
Use this chart to find clues as to
what needs to be done:
(copy/paste this link into your browser)
http://verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm
Your spark plug will probably be either wet
or dry, oily or sooty.
Your spark should be blue and jump
a gap of about 5 to 6 mm.
You will also have to verify that the
cylinder is capable of running
by checking the compression and
possibly a leak down test at some point.
These bikes should have a minimum of 130 pounds
per square inch of compression pressure
measured at the spark plug hole
while cranking with the throttle open.
Normal compression is much higher
like 170 psi but 130 psi should run.
If you get a low reading then you can
add a small amount of oil to the cylinder
and check it again.
If it goes up drastically then your
rings are faulty. If it does not
go up then it may have a burnt valve.
Since you have the smell of unburnt
fuel it sounds like you have
fuel getting to that cylinder.
Perhaps it is flooding with fuel
which would mean the carburetor
float valve is dirty, worn or stuck
open. This means the carb would have
to be rebuilt and cleaned.
If the compression is good and the
spark plug is wet then this might
be the problem. Usually the
carb will be dripping fuel out
it's overflow however.
Some fuel tank valves use a vacuum line
to one of the cylinders, if the
fuel valve leaks the cylinder can
draw excess fuel in through the
vacuum hose.
My bet is low compression or a tight valve
clearance preventing good compression
on that cylinder.
Good luck!
Wayne S.
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