They are within 1-2 oz's of each other. I would have no problem balancing it, but it does not seam like it is more powerfull of enough to warrant it, plus you need a very stable low rpm for landing approaches. My TH .75 idles at 1,800 reliably with excellent transition.

Well if you try to idle your ST90 that low, your transition will be shot to hell because you'll have to richen the low-speed need a *lot* due to the poor carby design.

ST themselves claim "Any idle below 2,500 RPM is considered good".

I think that probably rules out the ST90 for your application, unless you're willing to put a new carby on it.

As fantastic as the Tower 75 is (I own two and absolutely love them), there is definitely a very noticeable power difference with the ST 90. I have first hand experience with both engines installed on a SIG Hog Bipe biplane. The G90 pulls the plane with much more authority than the 75.

Regards,
Misterpanda

XJET,
If you don't have the idle super low, the Shoestring will keep on flying.[X(] This is a 7lb plane, that is very clean, and is running 8" of pitch.