All,

New problem just hit my 78 1/2 troublehead...

While accelerating in gears 1 - 3, my bike suddenly looses power for a microsecond, backfires and goes on. SOmetimes this happens several times in a row. I thought maybe plugs, changed them - no change. I thought plug wires, changed them - no change. I thought crap gas, I drained and put in fresh premium - no change. I thought accelerator pump on my S&S Super E - nope, its working as it should. My Compu-Fire ingition is timed right but I advanced it a couple degrees - no change, I retarded it a few degrees - no change.

Help!!! If anyone has any idea please write back.
ShovelheadGreg in Alabama

 

I'm thinking it is something in your ignition. I would look for pinch points and any place that the insulation may have worn away on your ignition wiring. Have you noticed it at any particular rpm? It could be a loose/poor electrical connection as well.

 

Check for leaks at both the intake & exhaust connections. You may be suprised at what you find.

 

If you still have an FXE ignition switch, replace it. They go bad and give the same symptoms. Also have a separate key chain for the bike. The weight of a lot of keys will kill the switches in short order.

 

Still a mystery! The key switch on my FXEF was replaced last year, I only keep one key on the ring - I know about the weight and wearing out a switch, but thanks for the tip.

While checking my intake and exhaust for leaks, I felt some air around my push rod tubes (front exhaust to be exact). I found a blown o-ring on the slide stay and replaced it, took a ride and it seemed to stop UNTIL I started back home and going up a big hill 3rd gear. About a 1/4 of the way up she popped twice and kept going. That was the only time the old girl made the same symptoms. I am going to change out exhaust gaskets this afternoon.

The wiring to and from the ignition is not frayed, the coil is not cracked. If she keeps popping I will try a new switch.

Keep those suggestions coming please.

THIS IS DRIVING ME NUTS!!!!!!!!!!!!!!!
ShovelheadGreg in Alabama

 

Have you considered a leak in your manifold

 

Yuppers I checked both manifold and exhaust with ether - no RPM change. Only happened three times today on a 80 mile ride. Tomorrow morning I am pulling both manifold and pipes and putting new exhaust gaskets in and new O-rings in my manifold.
This is really a pain in my ***! This situation NEVER happens under constant throttle, but seems to come alive under throttle up. Does NOT happen when I downshift, Just happens when I am giving the old girl gas...
I appreciate all your ideas - please don't stop now - WE have to get this fixed. I really thought I was done when I found the air flow coming from my front exhaust push rod tube.
In the morning I am going to replace all the cork gaskets on my pushrods, replace the exhaust gasket and the O-Rings in my intake.
ShovelheadGreg in Alabama

 

may want to check for wires shorting ,good location to start is wires going to tail light or maybe tail light itself.

 

usually a sag and then backfire (thru the carb) is due to a lean condition. if this started suddenly, check the float level and clear the jets, since you have the float bowl off anyway. you may want to look at the fuel tank vent, and petcock for flow.
If this has been a ongoing thing, the jetting may be off, or you have a intake leak (manifold seals) I hope this sends you in a proper direction, Bob.

 

This sound like mine when I bought it. The result was a dirty carb with the wrong jets. I would recomend pulling the super E(same as I have) and clean it or rebuild if needed. My shovel was so messed up it would only run on full choke. I had a local indy rebuild and rejet my carb (cost about $70 I think). Man...she runs SO SO sweet now. As good as my fuel injected twin cam.