Sorry to bring an old post back from the dead - not really the done thing. That is what the search engine is for. But I felt I had to comment.
Tyrol - Nice trainer. I have an AT40 myself (which is exactly the same as your Explorer 40 but with a different name and colour scheme) with a GMS 47 in it, just like yours, except I made a few mods to mine - I changed it to a taildragger, put in 2 aileron servos and sanded the dihedral out of the root ribs so that the wing is flat with no dihedral.
It flies very well and the 47 has enough power to pull it vertical - after sorting out some CG issues.

Some GMS engines can be a bit temperamental. There is a very long thread on here about getitng GMS engines to run properly. Click [link=http://www.rcuniverse.com/forum/m_2290854/anchors_2290854/mpage_1/key_gms%252Ctuning%252Cproblems/anchor/tm.htm#2290854]here[/link] to check it out.

The GMS is a great engine. I have a .47 and a .61. Both are great performers, but they both required the carb drilling described in the link.
My GMS 47 runs circles around OS and TT engines of similar size.
I run mine on 1 gasket (they have 3 gaskets installed as they come from the factory), hot plug and 0% or 5% nitro fuel OS #3 plug for 0% and #8 for 5%. You don't need lots of nitro to make good power - no matter what people tell you. I'm talking about sport flying here, not pylon racing.

Do the carb drilling and enjoy your GMS engine.

Whereabouts do you fly?