Motorcycle Repair: carburetor adjustment 1978 Suzuki RM80, air fuel mixture, air screw

Question
I can't find information about adjusting the air screw and idle screw for my 1978 Suzuki RM80, and any help would be appreciated.  Thanks!

Answer
Hi Jim,

The air screw has minimal effects on most
bikes. The real way to adjust it is
to run your bike at a slow idle using the idle
screw.

Then slowly turn the air screw in until the idle
falters. Turn the screw out until you
get the highest idle possible using
just the air screw.
Turn the air screw in about a quarter of a turn.

Turn your idle speed screw until the idle speed
is where you prefer it.

If your bike fails to speed up or down using
just the air screw at a slow idle it means
your carburetor pilot jet or passageways
may be plugged.

Yamaha makes a good carb cleaner to soak the
carb in to clean it well.

Make sure your idle jet is clear.

The air screw setting is only effective for
the idle air/fuel mixture on your bike. If you are having
problems at any other throttle opening then you
have something wrong with some other part of your
carburetion or fuel system.

Above idle the fuel is handled by the long
needle in the carb slide and the cutaway
on the back of the carb slide.

At full throttle the fuel is controlled by the
size of the main jet in the carbs center.

So if you have any problems other than at idle
the air screw will have little or no effects.

You must adjust the correct part of the carb for
each throttle opening to get a good running bike.

Of course you also need good engine compression and
good spark at the correct time.

Get back to me if you have any follow-up questions.

Good luck!

Wayne S.
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