81 shovelhead problems when in operating temperatures

[TH]

Hi guys,

I've rebuilt my 81 FX and I'm running into problems. The bike starts great and drives ok for a few minutes. Problems occure when the engine is at operation temperature. After starting, when the engine is starting to warm up, the exhaust is starting to make a strange popping sound. Within a kilometer it is losing power but it will revv up when I'm opening the throttle but it feels and sounds like shit. When I check the fuel filter it looks like it's not flowing enough gas to the carburator. I've cleaned and rebuilt the carburator, have a new petcock, ran the bike with and without the fuel filter but still having the same problem. For now I'm guessing if it's the ignition. I'm running a Crane Cam hi 4 single fire ignition. Battery is charging normal, the bike is starting fine so timing, coils and plugs seem fine. Is anyone familiar with my situation, or can help me out? My next move will be to switch the electronic to a points ignition.

Thanks for helping me out!

[JBinNC]

It could definitely be that HI-4, or the coil malfunctioning when warm.
One other possibility is the valve to guide clearance set too tight, especially the exhaust valves. The '83 or '84 XLs had that problem from the factory, and would have a dead skip or miss when hot. Cure was to remove the heads and hone .0005 - .001 out of the exhaust guides. That was a factory recall.

Jim