QuestionMy cycle ran find when stored for the winter. It was started several times all Winter.
It has developed a steady speed miss. I have put Lucas gas treatment and it stopped than the next time I ride it starts missing again. It has 26,000 miles and has been kept in garage and taken good care of.
It does not miss at idle or high speed or when giving it gas.
AnswerHi Willard,
It becomes more difficult to find a miss when
you have many cylinders. I would say since
you find the gas treatment helps that it
might be a fuel problem.
It also sounds like your problem is at
middle throttle opening which indicates
fuel problems in the center needle jet emulsion tube.
You might be able to tell which cylinder it
is by inspecting the spark plug colors
and condition.
If you ride it at the problem speed
and then shut it down quickly and
check the plugs for any sign
of misfiring. They might be black,
oily or sooty on the missing cylinder.
Hopefully it is just one cylinder causing
the misfire.
A timing light might tell you if it is an
ignition misfire but it sounds fuel related.
You might have to ride with each plug wire
removed one at a time and grounded to isolate the problem
cylinder.
A plugged emulsion tube would make the
fuel mixture lean if it was partially plugged.
They have small holes that can gum up over
winter.
You might try getting some safe Yamaha carb cleaner
and filling the carb float bowls with it.
Let them soak for a day and then drain the carbs
and run it again.
Even tiny amounts of moisture in the fuel
from condensation can repeatedly plug main jets and
needle jets. Try fresh fuel or some gas deicer (methyl-hydrate)
The fuel these days can gum up in a couple of months.
Fuel stabilizer is some help for winter storage.
If you haven't yet a compression check may
be a good idea to make sure all cylinders are
pulling the same load.
Any air leaks in the intake system can
cause a cylinder to run lean as well
but might affect the idle more.
Mid-range fuel delivery is handled by the carb slide needle
and the center emulsion tube/main jet.
The main jet would affect high speed more so.
Check that the carb slides are not sticking
in their bores.
Good luck,
Wayne S.
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