Bought a 79 about a month ago. Ran great had some electrical problems but got them fixed thanks to these forums. Took her out last weekend and was backfiring a little the first half of the ride but not bad other than that it ran fine. Turned around to go home and started mis-firing and running like crap. It died a couple of times at stop signs but started right back up. By the time I was about home I was only running on the rear cylinder. Every now and then the front would fire for a little than stop. Any help would be great.

 

Mine did that before. I pulled the spark plugs and plugged them in and wedged them between cylinder and horn (so spark plug body was ground) with plug gap looking out and turned her over. My rear wasn't firing put every now and then. swapped plug wires to see if it moved to other cylinder but it didn't. Swapped plugs to see if it moved but it didnt. Tried new wires, plugs, and coil but still the same. Finally bought a cheap electronic ignition and put new weights in. Better. Would only miss now and then. Started missing more, so I bought an ultima electronic ignition with multiple curves and no advance weights..no more problems. Have you looked at you're electronic ignition lately (mine looked pretty wore out and old) Have you checked to see if its set correctly, the gap between the trigger and sensor( should be .008 plus or minus .003 or .005 - .011). Have you checked battery for a low voltage condition (in case battery isn't being charged while running)

 

+1.
Go back over your electrical repairs once more and just make sure nothing loosened up or came apart.

Only other thing I can think of would be fuel delivery. Wonder when the last time that carb was cleaned and/or rebuilt?

 

Check your valve clearances on your front cylinder. Those Ironheads are notorious for the valve seats wearing away and causing either valve to not seat completely...I used to set the pushrod freeplay/tolerances "loose" for long rides. There was some clatter but both cylinders always fired for those long rides!

 

I make it a rule to check compression on any malfunctioning bike "just in case" with a screw-in guage. It doesn't matter if I actually suspect compression loss or not. It is useful to determine top end health. I'd also make sure that the intake manifold is securely sealed to the heads. BTW Harleys fire ACROSS the coil so if you like you can make a handy coil tester by hose-clamping or tack-welding two spark plugs together at the bodies. The "aircraft style" manifold clamps are the best. I throw the other sort away immediately. I'd remove, clean, and inspect the carb, blowing it out with carb cleaner and preferably compressed air.

 

1980 was the first year for electronic ignition. So unless it has been added by a PO this bike has points ignition.

There is a video posted on YouTube the shows how to check timing etc on a points ignition. Sorry i do not have the link.

 

Hey Mick, mine's a 79 and the old one in mine was exactly like the one in my manual which consist of a control module, sensor, and trigger. They actually call it a "breakerless inductive discharge ignition" in the manual. On mine the sensor would pick up one lobe on the trigger but not the other causing it to only hit on the front cylinder. My old one was a dual fire. The new ultima I purchased is a single fire.

 

Ah yes, i must read the FM again, eh. An electronic control module; contains all the solid state components, etc. Thanx.

 

No problem. If you're like me, I cant remember what I read hours ago, much less some time ago. I'm just wondering if tcoyle47's module could be bad like mine. Not sure how to check one out. I ended up buying new battery, coil, wires and plugs before getting a new module and fixing it. What really baffled me on mine was the fact the front would spark but not the back. Since it was a dual fire I figured the module had to be working for the front to fire, hence, it must be in the coil, wires or plugs. So, I replaced them. Still had problems. Bought a cheap electronic module and all seemed good for a few days. Then it wouldn't crank, would run battery down trying to crank it. (of course this was never at home always out somewhere) Once I would jump it off and get it going it would run like crap all the way home. Bought new battery only to have same thing happen. Finally bought the ultima ignition and has fired up every time since. With the exception of some carburetor fine tuning, she runs great.

 

check the rubbers at the carbs if there is a crack there it can cause the cyl to miss happend to my 79 fxe