Hi everyone,
I have an issue with the ignition on a 91 EVO FLHS. I have replaced the cam and push rods. I replaced the ignition since it was damaged when I bought the bike. This bike has me stumped on the ignition. I replaced the ignition with a compu-fire single fire setup. Not the most expensive or sought after ignition,but figured it would work for getting the bike running for my son to learn to ride bigger motorcycles.
Let me run down the mechanical side of things. I replaced the cam with an Andrews 23 cam and adjustable push-rods. Replaced the bearing and installed cam ending up with 165 psi compression for each cylinder so I knew I had the cam timed properly and proceeded to the ignition. I static timed the ignition and run the wiring. Once all was wired in I fired the engine, but only the front cylinder would fie consistently. Most of the time the rear cylinder was cold and not firing. I rebuilt the S&S carb also so I know it was providing fuel.
Since I was having trouble getting the rear cylinder to fire with this Compufire ignition. I removed the Compufire and installed a stock ignition and cannot get it to fire with the stock ignition. I check the new coil and wiring for ohms and power which are there and correct. Checking for spark with confirmed that the coil provides spark. I am leaning to the sensor and rotor as the issue. Is there an adjustment for the sensor plate to get the proper airgap? I know there have to ve some EVO specialist here so let me know what your thoughts are on this problem. After years of drag racing and 1000 HP dragster tuning this 2 cylinder is kicking my ***!

 

This may be a silly question but are you running a single fire or dual fire coil?
Do you have the right one selected on your ignition?

Oh and welcome to the forum.

 

I have both single and dual fire coils that I have for each ignition.

 

the way to do this is this - plugs out rear wheel off the ground rotate the engine in 5th gear clockwise ( the rear wheel ) put a small screw driver in the front plug hole and walk it around till the front is at TDC the line in the window on the left side of the motor -- to confirm put compressed air in the rear cylinder if the rear wheel turns you are 180 out if the rear cylinder looses intake air you are TDC front cylinder -- Note hold the wheel when spraying the air by hand so you dont get a false move on the rear wheel

now set the trigger to spec and start it up -- my kid and i have a divisional super gas car hahaahhaa find a way to throw away money faster owning one of those - jz

 

Thanks for the advise. I will give that a shot. As we all know, we may think we have it right and it is all wrong. The dragster is definitely a hog of another sort. Money hog! LOL

My son and I can tune that dragster with our eyes closed, but this has us stumped. We think it has to be something simple we are missing somewhere. I figured to get some other minds involve and may trigger an ahha moment. Thanks for any help.

 

make sure you have the right rotor cup and its installed correctly. its suppose to be the gold cup with 2 notches. and the dimple has to be in the notch of the cam. also if your running in single fire mode. switch the plug wires and pulse wires on the coil if it still runs on the front cylinder and not the rear its not the coil. another thing when you installed the ignition you could have pinched or broke a wire trying to get it in there. I have seen that happen a lot over the years.

 

Thanks for the suggestions. I do have the gold cup with the 2 notches and double checked to make sure the dimple key is seated in the cam properly. Right now I have the stock ignition installed with dual fire harley coil with no fire. I figured it would be a simple ignition to get it fired. I have the red, green and black wires from the sensor matched to the module wires of the same color going into the module. The wires coming out of the module are red, white, black, brown, violet and green. Also have the ignition switch wire connected. Someone who knows the wiring on this bike let me know what is connected where. I have the violet/blue connected to the VOES, the red to coil +, ignition switch wire to coil+, black to ground, white to coil -. Not sure where the green goes or the brown. Might be missing something here , but not sure. Could not find where the brown or green out from the module connected to the coil or anything concerning the ignition in the service manual. Thanks for any thoughts or suggestions.

 

This is the wire diagram for a 1990, I don't believe it changed to 1991 but I'll double check after work.Sounds like your heading down the correct path, sometimes you just have to walk away and come back to it.

 

Thanks for the diagram. Unfortunately the forum will not let me open it. Says I am not authorized. Just wondering if the brown and green wires coming out of the module have anything to do with the ignition setup. I am used to working with an MSD ignition and this one seems simple, but will not work. When I have the coil and everything hooked up I have 12 v at the coil with the ignition switch on. 3 0hms when checking the coil. Getting good continuity with the wires. Could this module be giving me the problem or the sensor just not collapsing the field to create a spark? Just throwing things out there. If anyone is good at wiring or knows this wiring harness please go through the steps you would wire the bike and where the wires hookup. Maybe I can see where I may be missing a hookup somewhere. Thanks again for the suggestions and time.

 

If you pm me your email I'll email the scans of the diagrams.