G'day engine lovers. I friend was given a GMS 47 which the original owner could not get to run reliably. He put it into small Sukhoi aerobatic model with an Bolly 11.5 x 6 and tried to get it to work. His fuel had some nitro but not much, and the oil had some castor but the engine just did not sound happy and worse, the muffler kept coming loose and eventually fell apart in the air. So after several deadsticks he too was ready to put the engine in the too hard basket.

The new owner is no newbie and was having no problems with several other similar engines.

Another of our club members bought a couple of Macs Mufflers and offered one to try on the GMS. The muffler was fitted, but this time a Bolly 12.5 x 5 was fitted (because it was all that was available) and the motor was given one last chance. Same fuel, same model just different muffler and slightly different prop.

Chalk and Cheese was the result. The motor is now totally happy, runs the tank dry if given the chance and hauls the little Sukhoi round with ease.

Any theories as to why a change of muffler and a relatively small prop change would make such a huge change?

PS. He is very impressed with the low cost and high quality of the Macs product.