O360 stumbling on initial takeoff power up

[petersb]

RV7A with O360 and C/S prop.

Recent change of behavior, coincides with warmer weather, on power up for takeoff engine dies then goes to full power. CHT and EGT's are excellent for rest of flight.

Next occurance occurs on downwind , low manifold pressure, I get the usual popping, especially if the airspeed is too high.

I know the popping is a characteristic of this engine, however, it is almost as if the engine died for a moment, enough so that I turned toward the runway before it recovered momentarily.

The manifold pressure is around 11 inches and rpm around 2000, airspeed approx 100 mph.

In colder weather I would get the popping on downwind if the throttle was reduced too quickly, this new behaviour during warmer weather occures even if the throttle is slowly reduced and the motor feels as if it stops momentarily


Any thoughts?

[riobison]

Hello Peter,

I went through the same thing on my 0360 in my RV4. I was sure it was in the carb to the point I was going to pull the carb and send it in for a rebuild. It was annoying and at times in doing a go around from my botched landings it was dangerous.

I debated in doing the Slick mags as I was at the 570 hr mark but ended up pulling the mags and taking them in.

The mags were worn out and the impulse coupler was ready to fly off. We doubt if they would have made another 20 hrs.

Rebuilt the mags, stuck them on and retimed everything. My stumbling was gone. Now I did change out my plugs to good used Fine Wire at the same time. The old massive electrodes were still good so shape so I'm certain that my problem was without a doubt in my Mags.

Good luck.

Tim

[petersb]

Tim

Thanks for the prompt reply

Will check the mags although they only have 159 hours since overhaul

My mechanic, like you thought, is thinking carb. The change in behavior seems to have followed an increase in daytime temperature which I assume would create a richer mixture

Regards Peter

[kamikaze]

For the initial stumble, the usual culprit would indeed usually be the accelerator pump in the carburetor ... but don't think that would explain the issues on downwind ...