I have 2 engines to chose from a OS 40 LA and a OS 40 FP. What are the difference in these engines in power and other specs?

Charles,

The FP had the Schneurle + boost port induction system, while the more modern LA has a pure Schneurle port induction system.
That would mean a power advantage for the FP.
The FP also has the right sized idle air-bleed hole in the carburettor, that the LA may need drilled, for it not to be eternally rich at idle (at least some LA engines were so effected, search RCU...).

On the counter-point, the LA has the copper flash coat applied to the cylinder sleeve, before the electro-less nickel (ABL?).
This would mean the LA is less susceptible to peeling its sleeve (but not immune to it, nevertheless).

There are no NEW FPs, maybe just unused examples, so where is your choice from?

just to let you know, OS has changed there terms a little, istead of ABN (aluminum Brass Nickel) They use ABL, which is Advanced Bimetallic Liner. It's still ther same thing as ABN, but a different name to throw you off.

sean

I would avoid the LA with its rear-mounted needle valve. It is hard to route the fuel line to it, the response to adjusting the needle valve is slower and the backplate screws sometimes loosen. And finally, it is goofy looking while the FP looks a real engine.

I bought a brand new LA and bought a slightly used FP from ebay. I have 2 planes. One is a Sig Kadet Senior and an Braun Airhawk 1. The kadet senior is alot larger (78" wing span, the airhawk is 58 1/2") so i think I'll use the FP on the Kadet.

The FP is much nicer looking, and needle valve is less prone to being snapped off in a crash. LA's plastic backplate is very weak, and lots of needles have broken off. If remote needle is important to you for safety, use the LA. Both are nice, easy to tune engines.

Pilgrim

As I always say, my OS 40FP is my best running and most reliable engine that I have (out of 5). Many people at my field have commented how nice it runs. Can't comment on the LA but many peope like it, some don't.

Joe