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


Does the intake system still look like this?  If so remove
the large right angle pipe before the throttle body and fly it again.
Don't worry about where it is getting the intake air. There are probably enough
leaks in the cowling to supply enough air for the engine.

That pipe is resonating somewhere in your RPM range. Probably around 5500 RPM. I don't know for sure if that is the problem but it is worth a quick try.

Is there an opening in the cowl on the bottom for the intake air?
If so take some pictures of it.

Paul Lamar