The factory Sure Start in my Hyper Viper was way down on compression, hence no real power. It was giving 16,000-16,500 rpm on a 5x3 black cox. It could go around and around but that was it, no stunt ability. I was also having a varnish issue with this particular engine (I ran four tanks of fuel through it to run in) and it was down on the quoted rpm. So I swapped the cylinder/head setup with a stock production engine that gives me a known 18,500 rpm. It has been too windy to fly lately but I will post what happens when I do.

I think the real issue with Hyper Vipers is the engine, not enough compression and a very loose rod socket. Once both those issues are solved they really scream. The tank can also cause problems and the elevator needs freeing as Jay said.

My personal (and therefore variable) opinion is that the Sure Start is an excellent engine and needs a little work to bring it up to scratch. Basically they are a Black Widow without the tank.

Luke.