OK.  I have been trying to solve this one myself and I'm getting no where.
I have an 89 Westy with a rebuilt motor.  There are nearly 15K miles on it.
The right rear cylinder is miss firing at times.  It generally works until
the engine warms up a bit and then cuts in and out at will.  I swapped the
ECU with no change.  I replaced the plugs and distributor cap with no
change.  The wires are new at 10K miles.  The spark seems to be very strong.
I swapped injector connectors but the problem remains with the right rear
cylinder.  I checked compression and it is very good.  I was about to check
the head cap nuts to see if they are torqued properly.  I am thinking maybe
there is a small coolant leak into the cylinder that "puts out the fire" but
there are no clouds of steam coming out of the tail pipe.

Any ideas what more I should do?

Thanks much.
Tom Miller