I ran it (the YS) on a test stand following the plumbing instuctions with check valves and fuel filters in place and it was amazing so I think the engine is stable. I was more concerned that the size may be small (the Seagull manual is really unclear as to weather this a 1.20 2 or 4 stroke plane.) If it's a 1.20 2-stroke plane then even a supercharged 1.20 4-stroke might be lacking in power.
 I have the Seagull Cap 232 .71-.91 that I put an ASP 1.20 4-stroke in and it seems to pull it around ok (the engine isn't completely broken in yet and it should produce more power once it is.) and the weight is only 1 pound diffrence between the two. I guess I'm just wondering if anyone has used a 1.20 4-stroke in this plane and how it worked out for them.