Motorcycle Repair: 1981 Yamaha 650 Special dies at high rpm, honda cx, plug caps

Question
My 1981 Yamaha 650 Special came out to play after being in storage for 12 years.  It had a problem when it went in and still does.  The engine starts and runs fine until I start getting into higher RPM's or jump on the throttle.  It starts to back fire and cut out until the RPM's come down.  I'm thinking spark is going away. Does the stator have a low and high speed winding that may be cutting out at hi rev's?
Paul

Answer
Paul,


-have the main carb jets and emulsion tubes
underneath them been cleaned well?
Check petcock or fuel valve for flow.

-do you notice any pressure/vaccum in the gas tank?
could be a plugged gas cap vent restricting the fuel.

-do rubber carb diaphragms have any holes or tears in them?

-check plug color, black is too much fuel, white= too lean.

-check for dirty air filter and air leaks around intake.

if it is the ignition I would suspect
in this order:

-loose or corroded battery cables
-the spark plugs
-plug caps 5k ohms
-plug wires
-connector or fuse corrosion
-ignition coil primary 2.5-3.9 ohms, secondary 8000-13000 ohms
-pick up coil (600-850 ohms usually ok)
-ignition module - replace to test.

No, the stator doesn't affect the timing
like on a Honda CX.