Updates:
Remember this is long distance trouble shooting.
Compression gauge was 15 lbs low when checking with another known engine. That makes them 95 and no faith in the gauge.
Everything to do with the valve train has checked out OK.
Confirmed spark at the (new) plugs.
Cyls 1-2-3-4+6 all making good power, 5 makes no power.
Think it's a lean problem.
Reading the plugs finds 5 of them all clean and at most, 2 have very slight tan color. In other words very good.
#5 plug is toasty brown, like a perfectly toasted marshmellow. Running very hot and lean.
Offenhauser manifold w/2 W-1 carbs.
Manifold gaskets checked, tight and no detectable vacuum leak. Cyls 4 and 6 running fine.
With engine running at about 1200 (to take the idle circuit out of the picture), #5 still not firing. Slowly dribbled gas into the rear carb. # 5 started firing and engine smoothed out. slightly more gas and engine started to stall.
I think we have a cylinder head with an internal crack in #5 leaning it out.
If the leak was any closer to the intake port, #6 would be affected too.
During the build I rejected 3 heads for cracks before the 4th magnafluxed ok.
Next thing would be to pull the head, What do you think???
