Gary Anderson

Working on a 35 year old Kohler generator. Weak spark on 2 cylinders from the magneto. Replacing the cap and rotor will run about $300 (dont ask) so I want to chack everything out forst.
Here's the info:
4 cylinder ford tractor engine (flathead) on a 6.5 kW Kohler Generator.
Good compression, fuel, carb, etc. but 2 cylinders have weak spark. 6-9kV on good cylinders vs. 0-3kV on weak.
Magneto is Fairbanks Morse FMX4B7A
Spark from mag jumps to a ground more that 1/2" from terminals 1 & 2 (both on left side of cap). While 3 & 4 wil barely spark 1/8" (right side of cap). Cap and rotor contacts are pitted, I sanded them smooth, still bad spark on 3 & 4.
Firing order is 1, 3, 4, 2. Points, condenser, coil, wires are new. Mag cam looks good, no obvious wear. Gap at .015".
Is there another problem that could cause this, anything in the magneto? Excessive play in the Mag shaft or drive gear?
Gary

Airpacker

What you need to check is the points dwell(cam angle) for a variation. A worn cam lobe(on mag shaft) or worn shaft will usually show up as a widely varying dwell angle. A shorted dist cap will also drop kv way down and if it is shorted between 3 and 4 you will have little to no spark there. Check the dwell first for variances.

Gary Anderson

Thanks Airpacker. I had not checked dwell yet because 1) I dont have a dwell meter (who does anymore), and 2) I cant find a dwell spec for this anywhere. I'm fairly sure it's not a mag lobe problem though. The mag only has 2 lobes and the firing order is 1, 3, 4, 2. I would expect that every other cylinder would be weak if 1 lobe was worn.
Sounds like a bad cap to me too.

Gary

Zoomnfun

carbon tracked cap