Motorcycle Repair: 1980 Suzuki gs550e, rubber diaphragm, vent line

Question
I have a 1980 Suzuki gs550e Running on three cylinders. have cleaned the carbs twice. good spark great compression. any ideas. Thanks Dan

Answer
Dan,
is the carb slide free and the rubber diaphragm good?
Have you tried spraying wd40 or such into
the carb intake, see if it fires on it.
Check for collapsing gas line or carb vent line
plugged. Check for intake rubber air leak,
again use your carb cleaner or wd-40 and
see if engine speed increases.
Any air leak can cause a drop in the vaccuum
required to pull fuel into the cylinder.
Could try a vacuum carb synch guage and see
it vacuum is equal on all the cylinders.
Any dealer should have a carb synch guage.