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

[hazydaze]

i learned when i rebuilt my last bike that changing many things at once in terms of the fuel delivery and ignition and carb can lead to chasing headaches like this. what i did was strip the bike and put all the old shit back on and then fine tune it from there before changing one thing at a time, like my ignition, then my carb// fuel delivery and so on. if that dont fix it then i would pull the heads like JB said and hone but easy fixes first i guess. i am no expert at all just a carport mechanic aspiring to work on old harleys so feel free leaving my two cents alone, good luck hope u fix it.

[JBinNC]

i learned when i rebuilt my last bike that changing many things at once in terms of the fuel delivery and ignition and carb can lead to chasing headaches like this. what i did was strip the bike and put all the old shit back on and then fine tune it from there before changing one thing at a time, like my ignition, then my carb// fuel delivery and so on. if that dont fix it then i would pull the heads like JB said and hone but easy fixes first i guess. i am no expert at all just a carport mechanic aspiring to work on old harleys so feel free leaving my two cents alone, good luck hope u fix it.

Definitely on point.

I would exhaust (no pun intended) the possibilities that do not require motor disassembly first, really a no-brainer. I think the ignition module is by far the odds-on choice for the problem. Coil next. I only mentioned the exhaust guide thing because I have seen it as described above, and the symptom is the same as the OP describes.

Jim