On pipe,

What weight does your model need to balance it? Is a normal .60 sized engine sufficiently heavy to balance the model without lead in the front?

If you are thinking of an engine to just putt around the sky with in a relaxing manner at part throttle (1/3rd to 1/2) with a minimum of flame-outs, I recommend that you avoid the ST line entirely.

While the design of their carbs is sound, their execution is poor, with a very rich mid range being a feature, even when the high speed and low speed needles are set correctly. This manifests itself as a rich "stumble" or reluctance to spool up when throttling on, which, at its worst, can put the fire out entirely. The STs run fine at WOT and idle all day if you want, but run 'em at part throttle and a great majority of STs will get the stumbles.

We have lots of STs at our field and there is a degree of variation in the performance of their carbs (call it manufacturing tolerance), from absolutely horrible (our resident ST G4500/WM Ultimate and an ST G90/Dragon Lady) to almost OK (an ST 2300/H9 Funtana 90 and a trainer with a G51 in it). You may be lucky to get a goodish carb but, then again, you may not...

Even the most rabid ST fan will admit that a carb change or a carb re-engineering job is a valid option if one wants great throttling on an ST engine.

OS's engines have the best calibrated, most consistent carbs of any widely available, mass produced two-stroke sport RC glow engine. If you want a hassle free in flight experience, get an OS two-stroke of the weight required to balance your model.

If you really want to buy a cheaper Chinese-manufactured clone engine in the .60 size, consider either the GMS .76 or the Tower .75. Both engines have delivered good service at our field and are sold by large reputable retailers (Tower and others) with proven after-sales support. The ABC Tower engine is a more performance oriented package with an unbaffled, free flowing, somewhat louder muffler whereas most of the ringed GMS .76s we've seen so far have come with finned, baffled mufflers that are very quiet.

Although manufacturing tolerances are greater on these Chinese engines than engines made in Japan, the GMS and Tower carbs generally come pretty well calibrated, and if you are unlucky enough to get one that's not well calibrated (there are a couple of documented examples of this) a reputable retailer should be able to exchange the bad part.