Diagnosing a High Speed Miss

[xs11]

Diagnosing a High-Speed Miss
by Phil Stewart

One of the frustrations of a high speed miss is the difficulty of diagnosing it's cause. Following are some simple tests that may aid in narrowing down the problem:

Ignition Breakdown

1. With the bike on the center stand and at the miss RPM (if you don't have a throttle lock [aka- cruise control], use a spring clamp or some other mechanical device on the throttle grip- your hand will not be steady enough, which will add confusion to what you are doing) try removing and reinstalling one spark plug lead at a time (pliers with insulated handles remove some of the excitement from this procedure) and see if all have nearly the same effect.


Note-you may have to resort to actually running in gear, to put
a load on the engine so it will act up. If you do so, adding a restraint to keep the bike from launching should it vibrate off
the stand, or in some other way get loose, is advised.


2. Try gapping your plugs down in the 0.020" range and see if the problem moves RPM (test it while riding).

Fuel Starvation
Two things to try while your are riding in the miss RPM range (remember to keep one eye on the road during these procedures).

1. Try moving the pet-cocks to the reserve and prime positions.
2. Try experimenting with the carb enricher (choke) lever.
3. Try opening your gas tank (if the vent gets plugged you will experience gas starvation)