ORIGINAL: on pipe
It is not totally out of the realm of possibility that it is leaking too much compression. I purchased a GS .40 a year ago and it had weak compression and would just pop a little. It had just enough compression that I questioned whether it was operator error, or if there was something wrong. I ended up sending it back, and it was replaced with a new engine with MUCH better compression right out of the box. Ringed engines do need more break-in that ABC, but they should have enough compression to start up, so you CAN break them in the rest of the way. After a couple tanks of fuel, most of the leak should be gone and it should have "decent" compression.
Ross
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Just don't be fooled into thinking that a ringed engine needs tons of static compression (non running) in order to run very well. Also, rings are prone to sticking some times and will display poor static compression when in other wise perfect condition. It takes a while to get used to ringed engines and all of their quirks.
Ed Cregger