What is a good prop for this engine? Tried a 7x6 useing it on my sig wonder tried to fly it today it just had no pull?

Do you have a tachometer? if not you should obtain one and do some ground testing to see what you particular setup prefers. For example I recently bought an ASP .12 that on a 7X6 Master Airscrew gave lackluster performance but just switching to a 7X3 let it rev into the powerband and it came alive. There are some good thrust /speed calculators out there to help you decide.

Try a APC 6 X 6. Mine turns 20,900 RPM on Powermaster 15%.

6x6 on an MDS .18 How long have you been running it that way?

Eight tanks so far. This is one of the best little engines I own. I have three! I will switch to a 6.5 X 6.5 APC next. Then a 7 X 7 Graupner. The Graupner is an electric prop, but works just fine on our OS .15 LA's we use for club 20 racing. The LA turns 16,400 on the 6.5 X 6.5. This little MDS is great engine. You will love it!!!