I bought the larger 61 size and have not been very impressed!! I ended up buying a carb for a Tower Hobbies 61/75 to finally get it to run properly and it has only moderate power output. I won't be buying another one. The story is that the engines are broke in and adjusted at the factory. I think that this is a bunch of hooey considering that some of the engines the low speed needle valves come out of the box completly closed!! Also based on my engine, it needs several tanks run through it to begin to smooth out, just like any other engine that needs to be broke in!!! I should have just bought another TH 75 engine that runs great, is easy to adjust, has better power output and is less $$$!!! [>:]