D140 W/B&S 656CC V twin: Loses one cylinder intermittently.

[Slobcat]

Magneto coils came in. Installed and engine running like new, or better.

I say "or better" because the air gap was way off originally (about 0.003" instead of 0.010") and it sounds like it is running faster than it was right before replacing the coils.

What is the RPM supposed to be with throttle lever in the detent before going into the choke position?

Looks like a lost spark system (plugs spark on exhaust stroke as well as compression stroke), so there will be a spark on every revolution for both cylinders.

 

[tom3]

I think most small engines have this, ignition trigger is on the crank flywheel, not sure on an opposed flathead, might be using every spark in one cylinder or the other? Glad to hear it's running as it should.

 

[Slobcat]

I think most small engines have this, ignition trigger is on the crank flywheel, not sure on an opposed flathead, might be using every spark in one cylinder or the other? Glad to hear it's running as it should.

It is an OHV V-twin and has two magnetos, so I'm pretty sure each plug sparks every time the magnet on the flywheel goes by.

I'll be triggering the tachometer function on my DMM with a coil of wire around the spark plug cable of one of the cylinders, so I'll probably have to select the 4 Cylinder scale to get an accurate RPM reading. I suspect the engine turns at about 3600RPM at normal operating speed and was wondering what it was dropping to with one cylinder dead.