flyrotary@lancaironline.net Mailing List Archive

In a message dated 6/20/2011 9:19:49 PM Pacific Daylight Time, bktrub@aol.com writes:

Brian,

This type of higher rpm roughness usually indicates an ignition problem. Since you are running Tracy's system I would expect coils to be a possibility. Good coil grounds are important. One of the other things I often question is are you using multi-lead coils? If you are they are usually a floating secondary. The high tension side of the coil uses both spark plugs to complete the circuit. One of the plugs fires normally, and the other fires backward. Frequently the backward firing plug will degrade quickly. If you are running a fine-wire center electrode this will be more aggressive. I saw this a lot on motorcycles 4 cylinders always were using the 2 coils with 2 leads each. Something to check.

Bill Jepson

I'm going to ground my airplane until I get to the bottom of this. I can tune it on the ground and it will run just fine all the way from idle to full throttle. I get about 5300 rpm at full throttle at 29 in hg. MP. I have 12 hours in the air so far but can't get past this issue. Other than this, the plane is an absolute joy.

When I get off the ground, when I go through around 5400 RPM, I start to get stumbling and engine roughness. At this RPM I am about 18 inches MP. Just below this point, I am making about 50% power and the engine will run smoothly.

I went to another airport and had a lot of roughness on takeoff, but I am used to it and so continued on my way to my home airport. When I got back I found out that someone at the other airport wanted to report me to FSDO because he thought my engine was going to blow up, but he didn't get my tail number.

So, I thought I had it sorted out before I flew today, but it's back to the drawing board. I've tried both leaning and enriching the mixture at all throttle settings, but to no avail. At and above 5400 rpm I start getting all sorts of roughness so I think that it has to be an ignition issue. My injector wiring is separated from my coil wiring, but could I be getting inductance between the different coil wiring?

I have a 93 13 BREW normally aspirated, 2.85 RWS redrive, EM2, EC2, 88x 74 CAtto Prop. This is getting to be really frustrating. It's got to be something simple that I'm overlooking. I don't know anyone with an ocilliscope, and have never used one.

Brian Trubee