jrvance
Member
I have a Fairbanks Morse mag on a Mosler CB40 2-cylinder 4-stroke engine that's not producing a spark. The engine spent the last 22 years in a box in my garage, I'm trying to resurrect it for my Fisher 404 project. The magneto has no distributor, so both plugs fire with each revolution meaning that one plug in each rev fires a "blank" i.e. it does nothing because that cylinder is in its exhaust cycle. During the first tests on the test stand, I was unable to start the engine (no spark then, either), but replacing the points and condenser seemed to solve the problem. The engine then ran fine, although it was rough at idle, even after cleaning/rebuilding the carb and multiple attempts to tweak the idle screw (Zenith carb). After accumulating about two hours total on the test stand, I started the engine one day and it ran for about 10 seconds, then died. No spark. I pulled the mag, disconnected the electrical connections, reconnected them, reinstalled the mag and ran the engine. It went 10 seconds, then died. No spark. I again pulled the mag, and began poking around with a multimeter. Checking the coil between the lead wire (connects to the points) and either of the outputs from the secondary coil revealed 200,000+ Ohms (didn't even tickle the meter on my analog gauge). I'm about to buy a new coil but I'm not sure if that's the right thing to do.
So my questions are:
What should the resistance across the secondary coil of a magneto be?
How do magnetos typically die? I'm pretty sure the points are still fine, but could my new condenser have died after only two hours?
Do coils often crap out just after starting when they're about to die?
Does a dying coil typically cause a rough idle?
Any help much appreciated
John
So my questions are:
What should the resistance across the secondary coil of a magneto be?
How do magnetos typically die? I'm pretty sure the points are still fine, but could my new condenser have died after only two hours?
Do coils often crap out just after starting when they're about to die?
Does a dying coil typically cause a rough idle?
Any help much appreciated
John
