Motorcycle Repair/1986 Madura

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Question
QUESTION: My Madura runs great at first start, but when it starts to warm up, is runs real rough.  What could this be?

ANSWER: Hi Mark,

It sounds like it might be getting too much fuel unless your valve clearances
are too tight. Have you checked the choke adjustment? The choke
has to be totally off when the engine is warm. Also check the air filter.
If your spark plugs are black that indicates an overly rich fuel mixture.
Sometimes a vacuum fuel valve on the tank can leak fuel
into the engine if the rubber valve is damaged.

Your spark plugs are a good indicator to what the problem is.
http://www.verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm

Let me know how it goes.

Wayne S
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---------- FOLLOW-UP ----------

QUESTION: as well, the bike keeps wanting to back fire through the first cylinder,  is this an  electrical problem or ignition??  I have  no idea how or what to do now.

Answer
Mark,

If the bike runs good when the choke is on then
you might have a carb that is running lean on fuel.

Soaking and cleaning the carb might help
and make sure the compression is at least 128 psi
on that cylinder.

Backfiring is usually because the cylinder is not
getting enough fuel or has an air leak on the intake
rubber tubes.

You could also try swapping spark plug caps,
wires or coils to eliminate the ignition coils.

Air leaks in the exhaust pipe can also cause backfires.
Check the exhaust for leaks.

You can try covering the back of the carb partially
to see if reducing the air flow helps
which would indicate a lean fuel/air mixture.

A cylinder leak down test can check for leaky valves etc.
if all else fails.

Check that the carb is filling with fuel by measuring
the float height or draining and measuring the fuel
in the bowl compared to the other carbs.

Keep an eye on the plug color as black is too much fuel
and light colors are not enough fuel.

The ignition pulse coils could act up when
hot but that is also a last resort after
confirming the rest of the fuel and ignition is working.

WS
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Wayne S.

Expertise

Licensed Motorcycle Mechanic, Knowledge of motorcycles from 1960 up, Japanese, British and most other brand motorcycle repairs.

Experience

Worked for Yamaha, Honda, Suzuki, Kawasaki British: Triumph, Norton, BSA Other: Most Scooters and Mo-Peds

Publications
Canadian Motorcycling magazine article

Education/Credentials
Licensed Motorcycle Mechanic

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