Don, I could have saved you some typing...

The pair of Magnum 70's I'm working with are both a couple of years old, and were pretty much broken-in as you suggested (the only thing I didn't do was add the extra castor, which is a trick I learned last fall breaking in an OS75AX). I'd also heard about the valve spring problem. After lots of difficulties (no top end rpm and a couple of fatal dead-sticks) last fall, I finally got so PO'd I sent 'em both back to Global with a letter that said (short version!) "... I can't make these run, maybe you can." Three weeks later, both engines show up in the mail, repair papers included that show about 10K rpm top and 2200 idle; they replaced the valve spings on one of them and added new head gaskets. All at no charge; I can't say enough good things about their service department.

Finally got enough of the snow off the ground last week that we got airborne again. I flew one of the reconditioned Magnum's, and once it was running it seemed stronger. I still have starting and idle problems (it wouldn't start using the onboard glow, and the idle was too fast), but those are probably more related to the inverted mount (idle's probably too rich) and the glow driver (battery?) than the engine. At least I hope so. I have yet to check the actual RPM with a tach, and the engine died after about 6 or 7 minutes airborne. That could be related to the idle problem, and I also need to dig the tank out and make sure all the internal lines are the right length. But at least it didn't die two feet off the ground during take off.

The plan now is another try at the inverted mount operation. If that doesn't work, I'm gonna side mount the engine and see if performance and reliability improve. Also went from a 12x6 to 13x6 prop, which should give me little more "umpfh". Whether that shows up as vertical pull or horizontal speed, I'm not sure.

Now if the sun will just stay out for the weekend... !

Fred