Motorcycle Repair/trouble


why does right cyl,fire stronger than the left,left also puffs (rich) black faint but obvious.mikuni carb.72'650 tiger,some backfiring ?

Hi Dennis,

If you have black smoke it might indicate over rich fuel mixture.
This can be improper jetting, plugged air filter or sometimes
a cylinder will be weak and blow black smoke because
it is not fully burning the fuel in the combustion chamber.
This can be from having lower compression than the other
cylinder or from a weak spark or weak ignition coil.

A cylinder with slightly higher compression and hence higher
vacuum will draw the fuel away from the other cylinder
at idle, this happens only on a one carb manifold.

Backfiring has numerous reasons, one is the fuel is
not being fired consistently due to poor ignition so builds up
and fires when it gets rich enough to fire.
This also means the cylinder might not be getting enough
fuel and cannot burn a lean mixture.
Again low compression, poor spark or lean fuel supply can affect this.

Check your spark plugs and if they are black that means
you have either plugged intake air supply, carb needs a rebuild
and cleaning. Spark is weak, try swapping coils if you have two.
Last resort, check if compression is the same on both cylinders
as the one with most pressure and vacuum is going to run
the strongest.

Make sure your choke is opening fully, check air filters.
Check spark plug caps.
Carb to engine gaskets or orings need to be tight to prevent air leaks.

Let me know if you have any more details on your carb or ignition setup.


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Wayne S.


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


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

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