Brian (and anyone else with more experience than me),
With my engine stand, primary injectors as small as 21 lb and secondary injectors from 30 to 50 lb have been used, with MAP up to 30 inches. Mixtures from lean misfire to rich misfire have been set with RPM up to 5800. Although misfires can be induced with mixture, at no time was there anything that could be considered a backfire and certainly nothing like a grenade. In flight, I have induced misfires with rich as well as lean mixtures again with nothing like the results you describe. My plane’s muffler is a hollow tube about 6 inches in diameter 3 feet long with a slightly less than 2” diameter outlet and two chambers inside separated by a conical wall. This muffler would seem to be more of a bomb than a grenade if a backfire were to happen. Doesn’t the fact that there is a viable fuel-air mixture in the exhaust system seem to indicate that the problem may be ignition rather than mixture? This is just a question, not intended to be an answer.
Steve Boese
RV6A 1986 13B NA RD1A EC2
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of bktrub@aol.com
Sent: Friday, May 13, 2011 3:35 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Engine Tuning
Since the weather has been cooperating lately, I've had the opportunity to put a few more hours on the airplane. On the ground, I can go from an idle up to full throttle and the engine will be smooth. But when I take off, it seems that as soon as I'm up a few hundred feet off the runway, I get hellacious backfiring at full throttle. I can mitigate it a bit by throttling back to about 5100 rpm, and turning the mixture knob to near full rich. It's getting to be a bit nerve wracking to take off thinking I've got it smoothed out and then get a series of hand grenades going off under my butt. I'm thinking that I'm still running too lean up at map address 106 or so. So, I go into the edit page and richen up the mixture around those addresses. I think I'm creeping up on smooth full throttle running.
The good news is that my coolant runs at 175 degrees and oil at less- so the cooling is more than effective, I just need to close up my air inlet a bit or restrict the outflow.