When I bought my second hand glow trainer, the engine was out of it . I mounted the engine today . I noticed that the engine is angled down. Shouldn't the engine be level or slightly angled up. The firewall is not straight up and down. This is causing the engine to be angled down. Should I shim it level with washers. How should it be mounted.

No, leave it like it is. It's called down thrust. There might even be a little right thrust built into the firewall. Chances are good that it's designed in. What plane is it?
Edwin

High lift wings like a trainer will climb like a home sick angel so thats a little down thrust to offset that.

It's a Hanger 9 Arrow with an Evolution 40 glow engine. Thanks for the info. I will keep the down thrust.

Yes, yes, Down and a smidge of right thrust. This is particularly important on most high wing cabin types.

John