Motorcycle Repair: 1995 Suzuki GS500E problem, 1995 suzuki gs500e, fuel air mixture

Question
I have been having some issues with my 1995 Suzuki GS500E recently. My engine loses and regains power--creating a back and forth jerking motion--while riding constantly at a certain speed in every respective gear. (For example, when I'm in 3rd gear, going 35-40mph this will happen. Or if I'm in my highest gear going 77-82mph.) The problem only gets worse when I switch from my reserve setting to the regular fuel setting. (I've been using the highest quality of fuel for about 400miles now with no improvements.)

Also, my bike has some problems starting up (white smoke out of the exhaust on start up, followed by black smoke a minute later) and will occasionally backfire after a loss of power. Oil levels are bellow full, but well above empty, and spark plugs seem okay.

Any help would be greatly appreciated. Thanks!

Answer
Hi Daniel,

Due to the smoking issues I would have the engines
compression checked. It should be over 150 psi
ideally. If it is lower there could be
tight valve clearances or some engine wear.

It could also be that the engine is overheating
due to a lean fuel/air mixture.
See if the fuel supply from the tank
to the carbs is running fully.

Another thing that can cause a fuel shortage
is a plugged fuel tank air vent.
This is either a separate hose
on the tank or is in the fuel cap.
If you open the cap and hear lots
of air pressure or vacuum then this
could be a problem.

The backfire is a possible sign of insufficient
fuel to the engine. If it is running lean
on fuel the spark plugs may be a light color.

If one cylinder is cutting in and out
a power loss could be felt when driving.
A compression check would probably show
if one cylinder's pressure is bad.

I would start with a general tune up,
check the plugs, air filters
and timing with a timing light.
Valve clearances and compression should
be checked.
Check the fuel supply flow and
clean carbs.

It might be one of the carbs is not getting enough fuel
or has a bad plug or spark plug cap causing one cylinder
to cut out.

Try to isolate the problem to compression, fuel or spark.
If working on the fuel shows no improvement then
check the ignition timing with a light and see
if it fires correctly on the static and advanced
timing marks.

Air leaks around the carb intake and engine can
cause a fuel lack as well.
Check the rubber tubes and gaskets there.

Good luck!
Wayne S.
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