I agree about S-T's requiring quite a bit of breaking in. Had lots of trouble with my gs 40 right off the bat. You might want to try a different/new glow plug, I noticed mine making a different noise at full throttle, then it quite at idle on the deck. New glow plug fixed everything. Don't know what kind of Glow Plug you're running, but (my opinion here) if you're not running an OS you're asking for trouble. OK, Enya plugs are good too. Don't buy a cheap glow plug.

A 10 x7 plug on a .45? I'm pulling an 11x6 on my 40.

Andy