Option 1 & 2 are effectively made by the very same company.

There are only a few cosmetic differences between the two engines, but the GMS has the slightly larger bore.

All three can be a handful to get running & tuned initially, yet I've had one of each start right up out of the box and then only need a click or two of adjustment.

My out of box experience has been mixed.


The Evolution should have it's blue limiters RIPPED off when you get it.


Knowing all three, I favor the GMS for it's slight power advantage and the T.H. for Tower's parts stocking. ( It's a snap to get something sent to you quickly when you need it. ).

Both engines would work well, and mufflers, etc. are interchangeable between the two.

My BIG grip with the two engines is the placement of the muffler bolts.

Many engines have you screw in the cap screws into the muffler from the opposite side of the cylinder head.

In the .75 TH and .76 GMS, you need to do this from the same side as the muffler. The screws affix into the cylinder head instead of the muffler.

The problem is that there is not much clearance there, so if the engine is cowled, things get problematic.
You must use the supplied allen key ( and hopefully NOT loose it! ) or cut down your own. Even with the shorter key this arrangement is still annoying.

I don't know which Pitts muffler you are looking at, nor how you will be accessing or mounting this, just be aware of the cap screw matter.


Remember though that the weight may also force you to do some redistribution of components, since the 2 strokers are going to be lighter.