I have a question about the engine in the title. With a 12/7 APC prop and Eric Clutton's Old English Diesel fuel I can over compress the engine but not under compress it. At least I'll get to the point where I don't dare to back the compression screw out any further. Is the engine under propped? Another possibility could be too much ether, I doped the gallon can (most of the gallon unused) with the contents of a can of John Deere starter fluid. A Norvel 061 with an RJL head would not start before it was added.
Today I ran an OS 10 FP with a Davis head and it would miss as I backed the compression down. I'm a little confused about the .40. Ted

Eb -
Sounds like you need a head gasket. The 40LA comes with one - I don't know about the 40FP. It can be easy to miss - maybe it's still stuck on the glow head.
Just a guess..
Lee

Ted, I'd try a 12x6 and see what happens, I use 12x7s on my .50 sized engines and they turn in the low to mid nines depending on which engine.

See here, http://www.rcuniverse.com/forum/m_5814069/tm.htm

If the others run ok and you can not go undercompressed on adjustment you are most likely missing the head gasket you must use it on OS , if still a problem add a second one my TT61 had the same issue it took 3 but now a hummer martin

Thanks I'll look for the head gasket.

Ted

I Checked, no headgasket, thanks guys.

Ted