Rough Idle, Low Speed

Hi all,

My RV8 flew for the first time today. It has an AFP injector, IO360M1B, dual lightspeed ignition, three blade Catto fixed pitch prop. There are two issues:

1. At idle, it is very rough unless the mixture is pulled out about a third. If you lean it to be really smooth, then application of the throttle will see it hesitate before powering up. With it a little less lean, it is not quite as smooth but will power up pretty easily.

2. While in the initial flight testing, it runs very smoothly from about 65% up to full power. With the power pulled back to about 13 inches and 1400 RPM, it seems to miss some. Not constantly, but enough that my test pilot did not want to stay at that RPM. This could be worrisome on approach.

Since I have dual lightspeeds that seem to be performing normally, we thought this might be a fuel/servo issue. Anyone have any idea how to investigate the problem?

I would call AFP first, but it sounds like your idle mixture, at the very least, is way too rich. What HP and what is your fuel flow at full power? You should be at about .9-1gph/10hp. If you are seeing over that amount, then your injection system is setup too rich. I would recommend first looking at the idle mixture. I don't know at what rpm the idle mixture comes into play, but it's where I would start, because leaning cleans it up.

I had the opposite issue yesterday. I turned my mixture 1.5 turns richer (counterclockwise) and everything got smooth. Sound like you needed to do a little of the opposite?
Good luck!

My idle mixture was way too rich which caused exactly the same symptoms. Engine would die on rollout if I forgot to pull the mixture back from cruise setting. There are procedures in the manual for adjusting it and that's an adjustment they can't do at the factory. It's expected that the engine builder perfect that setting in the field.