Backfiring

[ChiefSchutter]

I have an 86 Heritage that has started to backfire at about 3000 RPM. I have an S & S Super E carb and a Crane Hi-4 single fire ignition. It's backfiring through the exhaust with a flame coming out of the pipes. It runs fine in lower RPMs but as soon as I get to 3000 RPM in any gear it will continually backfire. The only time it doesn't backfire is when in neutral and I rev it up. Any ideas?

 

[dynarider]

Saw this with someone's bike on a dyno last summer. (Dr.Dyno - Dyno Testing All Motorcycles,Expert Tuning American V-Twins) He will answer some questions too.
I believe he changed to a smaller jet on the circuit involved.

I would say you're running rich, and to check your plugs for fouling. Check all your plugwire and coil connections.

 

[glider]

I have an 86 Heritage that has started to backfire at about 3000 RPM. I have an S & S Super E carb and a Crane Hi-4 single fire ignition. It's backfiring through the exhaust with a flame coming out of the pipes. It runs fine in lower RPMs but as soon as I get to 3000 RPM in any gear it will continually backfire. The only time it doesn't backfire is when in neutral and I rev it up. Any ideas?

I'd start with checking the ignition curve on the Hi-4. It may be over advancing at that point. It's unlikely there's a jet problem if it was running OK before this started.

 

[dynarider]

Well, the OP didn't say what has been done to the bike lately. I get this all the time with computer users who say, "this just happened" or, "it has started doing this ...", and usually it is later that you hear what it is they did.

So, I am assuming something has changed and the S&S ended up being rich.

BTW, Dr. Dyno was working with an S&S carb when I saw him do his thing. It was rich and he added lollipop baffles to the bikes drag pipes after cleaning a sparkplug. All the sudden, PRESTO! It was a different bike all together.