QuestionMy bike idles ok but at around 55mph or so theres a hesitation. I was thinking of changing the coils but im not sure if this has coils or a coil pack. Im not sure where to start to be honest. Everything is packed together on this bike.
AnswerHi Scott,
The carburetion on these bikes was set very lean
to meet the epa pollution standards.
This is the most common cause next to dirty/plugged
main jets inside the carbs for a mid-range hesitation.
This requires a physical cleaning of the brass
main jets in the carb bowl center or you can try
shimming the slide needles up slightly if the carbs
are very clean.
The next most common cause of hesitation is sticky carb vacuum pistons,
and/or leaking rubber piston diaphragms.
These can be checked without removing the carburetors from the bike.
The top edge of the rubber may be leaking air
or they may have small holes in the rubber.
Any intake air leaks can cause problems
as can a lack of fuel from the tank.
A good or additional fuel filter is recommended to prevent
carb problems.
The main jet size could be increased slightly
to see if it helps the problem.
Also check that the spark plug cap resistance
is not too high. About 5000 ohms is common.
The hesitation you mentioned is very common
so changing coils would be a last resort
as it is not usually the problem.
So try shimming the needles or checking
the slides and rubber diaphragms first.
If you notice no difference try a larger main jet.
The carbs have to be very clean before changing
anything as any fuel varnish or gum in the jets
can cause problems. The mid-range throttle is mostly
controlled by the slide needle and the jet tube
it travels in. Also the main jet is involved
in the 3/4 to full throttle range.
I would try experimenting with richening
the mid-range fuel before changing any
ignition components and check
for any vacuum or air leaks around the carbs
or hoses.
Luck!
Wayne S.
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