I run the tuned muffler(3248) the muffler and header are close together. 15% synth, 5% castor and 5-7 % nitro.I could not tach it because of lack of light. I will try to tach it tomorrow. I preheated the engine with a heatgun to about 160 farenheit for the first start. wot and a little rich on the needle.I ran it for a while like this, then I leaned it a bit for a while, then I richened it a bit and so on. I monitored the temp all the time and the hottest it got was 212 farenheit, mostly around 180. I did this for tre tankfillings. I dont consider the engine fully broken in yet, but ready to get airborne.I will try to get a 12-4 tomorrow and give it a try too.