Just started breaking in my Tower .75 glow engine. I've run about 16 ounces of Wildcat 10 % nitro, 18 % oil (syn/castor blend) through it so far. I've been using the method recommended for ABC engines...e.g. run full throttle at slightly rich setting folloed by a cooldown and then back to full throttle running slightly rich. My question is I'm showing about 12,000 rpm using a Master Airscrew Scimitar profile prop 12x6, and I realize that I'm not running at normal lean so it will run faster..but I know that I'm pretty close to full rpm. Is 12,000 about normal with this engine at this stage in break-in?? Can I expect the rpm to come up with furthur time?? Let me know if this sounds about right, or if this engine should be turning faster........By the way I'm running with a 2.5 inch plastic spinner on also. Thanks.

Flintlock, my reaction is that 12,000 on 12x6 w/10% nitro is a bit on the fast side. For your first break-in run, I would start with sloppy rich needle setting, and then once you have it started, turn the needle in just past the point where it goes from four-cycle to two-cycle. This would be a definitely rich setting, and you should be seeing plenty of exhaust. I would not be looking for 12,000 rpm until you are maybe into your fifth tank. Tach your engine at WOT but needle just over the two-cycle break, and let it run five minutes at that setting. Then shut down, let it cool to the point where you can touch your finger to the head without getting burnt (figure at least a 10-minute cool-down). Then on subsequent runs turn your needle in for a few hundred rpm and go another five minutes. After the engine is running at a stable speed, give the fuel line a (brief) hard pinch and listen for a higher note. If you don't get it, or the engine stops, open the needle a few clicks, because you are at peak. If you do get it, leave the needle alone until you finish another 5-minute run/10-minute cool-down. I broke in a Tower .75 a month ago, and got it turning a 12x8 apc prop at 11,100 static on 15% nitro, pulling an old 60-size Easysport I re-built. I got a lot of comments on the vertical acceleration out of my low and slow passes. It pulls straight up indefinitely.

Those numbers sound pretty good to me at this stage, but you should start peaking the engine now for short bursts and cooling down. You could help the engine break in faster by bench running using a 14x6 prop cut down to 10 inches and balanced to get it up to rpm quicker.

Otherwise, just put it in a plane and fly, as flying is the best way to break in a motor. The 12x6 prop is a good choice for flying , and as the engine breaks in it will develop more power. HTH

Thanks for the responses.......I figured I was in the ballpark with those figures. This engine was practically knocking over the sawhorse (wooden) I had it mounted to. I think it's gonna be a strong puller; it also idled very well and accelerated rapidly.