I have a 1976 FXE. I replaced a cracked coil and got the bike started, went for a test ride and noticed it missing and backfiring thru the carb. I removed and cleaned the carb, drained the gas, replaced the points and condenser and put in new plugs. Starts right up idles fine has good power as long as you are on or off the throttle. Holding steady at mid throttle it runs terrible. This is my first Harley but I'm pretty handy with tools, but this has me stumped. Any ideas? Thanks for the help

 

Backfiring through the carb...first thing I would look for is a vacuum leak.

 

vacuum leaks are a thing most come to know is the real issue -

the intake O Rings are a thing to check first, when you cleaned the carb did you happen to replace the intake seals - if not its the next thing you need to do, in my shop we rap USA made electrical tape around the intake and the heads holding the o rings in place it also aids in the seal - good luck and welcome -- johnjzjz

 

Check the seal behind the carb for fit and cracks

 

Do you have a service manual? This is a must to have. Sounds to me to be an intake leak. Those intake seals get brittle. They are not expensive, replace them. When you go to tighten the clamps, do not over do them.

Be sure to replace the o-rings and seals. Get a rebuild kit for the carb., clean it and rebuild it.

What carb is on it?

 

Check for leaks with either carb cleaner or propane. Idle will change if you have a leak.
If that's not the problem, run without air cleaner, put your hand (or leg) over carb inlet while running steady. If problem goes away it's too lean low/ intermediate jet. If it gets worse, too rich.

 

Mine ran that way when I first got it-40MM Mk C.V....plugs were black, about 25 miles per gallon no intake leaks so I reduced the low speed jet for a smaller one and cleaned her right up, plugs the right color and runs great all way round, who ever had it before me screwed up on jetting, just another thought, could be any of the above issues...what kind of carb are you running?

 

I was not able to look at it until today. Used propane and carb cleaner I'm sure there is not a vacuum leak. It is an S&S Super E carb. I will pull it tomorrow and see what jets are in it. The plugs were pretty black when I changed them. The miss was an occasional thing the few times I got to ride last year but now it makes it unrideable. Cleaning the carb had no change in its performance. What size jets should I be running? I know with snowmobiles elevation has a lot to do with jetting. The bike was being run at sea level and I'm at 2500'
Thanks for all the help, and a shop manual was the first purchase I made!