I have persisted with my axe .25 cobra motors despite the rods being a problem. Finally sorted the rod issue out by useing a GO PRO rod for about $23, the R7 NOVA rod works as well but the GO is less than half the price. Latest engine has got about 30litres (7-8gallons) on it with the rod being changed at the 5litre mark and it is still in great nick.
I have tried a few pipes on these engines and finally settled on the JP4, that was until I tried the GO 2072 pipe on it. The pipe really showed the true potential of this engine. Still has stump pulling low but now it pulls that hard all the way through to a screaming top with about 1 1/2 minutes extra run time. This pipe will not be coming of this motor any time soon.

Go the axe (with a better rod) you wont look back.