I'm sure this problem has come up several times before, my 73 isn't firing on the rear cylinder. I've changed plugs 3 different times and still no change. has good compression, spark and fuel. I'm running a crane cams hi-4 electronic ignition. with everything I have checked I'm leaning towards a bad coil. any input from the ironhead gurus on what else I could check before buying a new coil?

 

Hi 4 allows the this to be single fire or duel fire if its in the single fire mode AND YOU DID NOT SAY what cylinder---- soooo switch the wires and see if the other cylinder goes out instead - then you know its the ignition not the coil

 

I did say. it's the rear cylinder. it is firing just real weak.

 

how do you know that - you have a meter on it and read the voltage - your problem could be wires as well

 

The only good test for a bad coil is to replace it with a known good unit. It is useful to always have a spare on hand specifically to test situations like this. So if you do buy a new coil and it does not solve the problem, it is not a waste of $s. A spare coil is like any other tool in the tool box.

For me this also applies to the generator and solenoid. Always spares in the shop.

Another possibility is a bad ignition module [Hi-4]. Do you have the instruction sheet? There is a warning on the last page to never crank the engine with no grounded spark plugs in the wires ...

http://www.cranecams.com/uploads/ins.../90004001b.pdf

Try swapping the spark plug wires, as suggested above. This is something else to have spares for.

Loose wires/connections on the coil?