I'm getting ready to break-in a new TT .91 4c and have heard it takes some time to break it in. Can anyone who has broken one of these in give me some advise and also recommend fuel?
Thanks,
Chris

Follow the instructions. Pay close attention to what it says about the first tank.

IMPORTANT: YOU MUST INSTALL THE CHOKE PLATE ASSEMBLY OR THE ENGINE WILL NOT RUN WELL!!!!

I broke them (I have 3) in using 10%nitro 20%oil 70/30 Synthetic/Castor mix. Took about a gallon, first 4 tanks (14oz) on the bench the rest in the air.

I fly them all with 15% nitro, 20% oil 90/10 Synthetic/Castor mix. Fox Miracle plug is the only one I have ever used.

Be very sure you check all of the bolts and tighten them after the first 30 minutes of running. Let the engine cool first. Recheck/set the valves at the same time and be sure the engine is stone cold when you do the valves. Re-check the bolts and valve clearances after you have run about another gallon of fuel.

Good running engine. I have had zero problems with mine and have been flying them since 1996.

Dan

For break-in you want a big flat prop...large diameter, low pitch. I like an OS 'F' plug in it. The instructions say to not rev over 5K for the first few minutes. You want this guy to be slobbery rich through the first 2-3 eight ounce tankfuls. Very gradually lean it out over the next 6-8 eight ounce tankfuls. Yea...all on the bench. After the last tank you should be close to full lean. Go in and check/set the valves for proper clearance. Put it on a plane and fly it kinda rich for another gallon or so. I liked the APC 15x6 on mine. It turned 9200-9400 on the ground and made a massive amount of thrust. IMO, running ANY 4 stroke over 10K on the ground is not a good idea as it will unload in the air...then it will be going WAY too fast for all those moving parts. The only downside to this engine IMO is its weight...it's a real pig at over 26 ounces!

I ran my last one for 15 minutes and then flew it. It held a steady idle and had a wonderful transition after the first tank.