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

Brian,

This type of higher rpm roughness usually indicates an ignition proble= m.=20 Since you are running Tracy's system I would expect coils to be a possibili= ty.=20 Good coil grounds are important. One of the other things I often question i= s are=20 you using multi-lead coils? If you are they are usually a floating secondar= y.=20 The high tension side of the coil uses both spark plugs to complete the cir= cuit.=20 One of the plugs fires normally, and the other fires backward. Frequently t= he=20 backward firing plug will degrade quickly. If you are running a fine-wire c= enter=20 electrode this will be more aggressive. I saw this a lot on motorcycles 4= =20 cylinders always were using the 2 coils with 2 leads each. Something to=20 check.

Bill Jepson

I'm going to ground my airplane until I get to the bottom of this. I= can=20 tune it on the ground and it will run just fine all the way from idle to = full=20 throttle. I get about 5300 rpm at full throttle at 29 in hg. MP. I have 1= 2=20 hours in the air so far but can't get past this issue. Other than this, t= he=20 plane is an absolute joy.

When I get off the ground, when I go through around 5400 RPM, = I=20 start to get stumbling and engine roughness. At this RPM I am about 18 in= ches=20 MP. Just below this point, I am making about 50% power and the engine wil= l run=20 smoothly.

I went to another airport and had a lot of roughness on takeoff, but= I am=20 used to it and so continued on my way to my home airport. When I got back= I=20 found out that someone at the other airport wanted to report me to FSDO= =20 because he thought my engine was going to blow up, but he didn't get my t= ail=20 number.

So, I thought I had it sorted out before I flew today, but it's back= to=20 the drawing board. I've tried both leaning and enriching the mixture at a= ll=20 throttle settings, but to no avail. At and above 5400 rpm I start getting= all=20 sorts of roughness so I think that it has to be an ignition issue. My inj= ector=20 wiring is separated from my coil wiring, but could I be getting inductanc= e=20 between the different coil wiring?

I have a 93 13 BREW normally aspirated, 2.85 RWS redrive, EM2, EC2, = 88x=20 74 CAtto Prop. This is getting to be really frustrating. It's got to be= =20 something simple that I'm overlooking. I don't know anyone with an=20 ocilliscope, and have never used one.

Brian Trubee