I did take the exhaust pipe off and substituted a 3 foot bent pipe without muffler. No change, so I took the manifold off, cleaned everything up, (didn't look that bad) and put back with new gasket and Permatex ultra copper sealant. No change in popcorn.Drop the exhaust pipe so the exhaust is coming right out of the manifold. That will narrow down where the 'popcorn miss', isn't!
Have they changed 100LL in the last 20 years? Used to be that it actually had lots of lead and when you pulled the plugs it would adhere to the elements - had to regularly sandblast them.Chris,
I spent 5 years refueling aircraft of all types from 747s through home built ones and from that hands-on experience I actually know something about Aircraft fuel designations - including "Avgas" 100LL.
100LL is a designation of two primary characteristics in this fuel - simply 100 from it's Octane level (the same Octane rating as on gas station pumps) and the lead content ---Low Lead--- . NOT high lead but rather LOW lead compounds directly affecting the octane. Read paragraph 5 here: EPA Takes Final Step in Phaseout of Leaded Gasoline | About EPA | US EPA
If you think that the valves are sticking, REALLY think that, then either you or someone else is just going to have to pull the head and check them out. If they're sticking it could be old, bad fuel used in the past, poorly adjusted carb in the past or even something like a damaged push rod or even a poorly seating valve.
Hoping that pouring something in the gas tank is your answer (if it is a sticking valve or such) is a bit over hopeful. I find it helpful to work from a position of specific knowlede instead of just hope.
All the best to you.
- Joe -