I'm building a Mojo 60 with removable wings right now. I'm going to use an SK .90 engine. They are $100 and it should swing a 14-6 or 15-4 prop easily. It's not too heavy.

I was going to use a TH .75, but I know from experience it wouldn't have enough power.

I'm not sure how many guys actually weigh their planes. I have mine completely framed up. I put the entire fuse on the scale and recorded the weight. Then I weighed the wings and the aluminum tube. Then I weighed the servos, battery, switch and RX. Then I weighed the gear and lightweight foam wheels. Weighed the CF tailwheel. Weighed the engine with muffler. Weighed the 10oz fuel tank.

Without covering it weighs right at 6lbs. That doesn't include hinge glue for any of the control surfaces and it doesn't include the servo extensions or the motor mounting bolts. Doesn't include the foam under the RX or the tank.

This thing will weigh an honest 6lbs 4oz when it's done. I'd bet money on it. And just to head anybody off ......... NO! I'm not a newbie builder and I don't build heavy. [>:] Anyone who has one with removable wings will tell you that modification adds 4oz-6oz of weight.

Given the projected weight of 6lbs 4oz, I KNOW the TH .75 won't work at this altitude. I'm QUITE familiar with these engines and pulling weight vertical at 5973' above sea level. The TH .75 would do the job, but it would be sluggish and I ain't building a Mojo just to have it sluggish when punching from a hover. I want POWER! Lots of it!!

If I was you, I'd skip the ST75. I think XJet is right about the carbs. I hate ST carbs. They are like a light switch. You can dial it in to idle. You can dial it in for wide open. But trying to get consistent mid range performance out of a ST carb is just stupid. It's a waste of time.

The YS 61 and the OS 70 will both be very disappointing in this plane. The 120 will be too heavy.

If you have lots of cash, get the Saito 100 or the Saito 115. If you're on a budget, consider the SK90 or a Magnum 91 4-stroke.