The fuel was 10% nitro and I had already used about half the 5 litre can, I have since used the rest with no problems. I am sure there was a crack at first because in hindsight I remember when I first started it and it would not rev it sounded strange 'like a leaking exhaust. I don't run a silencer so it was a bit more difficult to hear. I have also being flying my gas planes alot so maybe not quite in tune with the four stroke sound. What I must say is it did fire before it blew,I guess it turned over about 3 or 4 times before it went bang.