I saw this issue referenced in another post but couldn't find any fixes or solutions. Basically on the first or second takeoff of the day, the governor wants to run a little on the high side, 2750-75ish or so so I back the prop off a few turns to keep it at 2700. After the engine gets good and hot, or even after being shut down for an hour or so the governor than holds the prop right at 2700RPM which is where I originally set it. I don't see this as being a huge deal as long as I don't overspeed for more than 5% and 3 seconds, but if its fixable I'd like to make it perfect. Any ideas? I could probably go back and make sure the low pitch stop is set correctly, but that wouldn't explain why it needs to get nice and hot to hold the right RPM.

I think if you'll attach a digital tach to your engine and run a few checks you'll find that the analog tachs your Maule came with are not precise enough to account for renegade RPM's in the neighborhood of 50 to 75. My tach is 200 rpms lower than actual. A Horizon P-1000 digital tach replacement is in the plan.

I suspect the difference you are seeing is related to the analog tach being cold and then warming up.

Interesting thought, when I checked the tach calibration with a trutach it was spot on, but everything was also pretty warm at the time.

Just loaned a Hartzell prop out for install on a reman lycoming O-360 C1F installed on a MX7-180. He is reporting the same issue with surging of the prop more when cold, but still some when warm, stabilizes until major power changes.
The aircraft had a C4F, and the fresh reman C1f engine also has a new McCauley prop governor, and electronic tach. No mechanical tach to confirm readings.

The used prop has 1000 hours TT and was just back from the prop shop for a desludge and paint, but was not overhauled. The HC-C2YK-1BF with F7666 blades was used.

Next plan is to swap out with another prop to try and diagnose the issue and determine if this is a prop issue or a issue with the new governor.

Is anyone else using the McCauley governor on this engine and prop?

Any feedback is appreciated. We will keep this post updated as we go forward.

Decided to take the prop off the M-6-180 and swap to sort out the issues with the MX7-180 surging. The replacement prop is working flawlessly according to Chad. The prop shop is tearing down the other prop to investigate, and suspects some corrosion in the hub. Since I just bought that prop used, I'm hopeful it is repairable. More if any surprises occur.

Well, the prop shop had bad news, the props prior owner or a ham fisted A&P somewhere in its history didn't know how to disassemble the prop or put it back together correctly.
Problem solved for Chad.
Big problems for my prop.
Unsure seller will make it right at this point.

Just wanted to update this post in case anyone else has the same issue. Every winter I have noticed my prop not govern correctly, it would run high at the first takeoff in the winter, and then subsequent takeoffs would run about 100RPM lower. More recently I noticed a small "hunting" of the RPM in cruise, about 75RPM or so. On very cold says, the prop would try to overspeed during takeoff unless I pulled the prop way back. After talking to a prop shop, the governor came off and a new one went on for a couple reasons. They wanted $1400 for an overhaul and it sounded very likely I would need new fly weights and a whole list of SBs complied with so the new governor made more sense (Same price for a new governor as it was for the overhaul plus extra parts). Also, I found out the McCauley C290D3G/T29 that I had has been superseded by a DC290 series governor that is much more resistant to transient overspeeds due to a newer design.

The final thing I found during the whole process was both Hartzel and McCauley suggest setting your low pitch stop on the prop to limit your static RPM on the ground (zero wind) to between 25-100RPM below redline. That way, full throttle at the takeoff run you're limited by the pitch stop and then as airspeed increases, the governor takes over. One of the advantages of this is that you can verify your engine is making rated power if you are in doubt.


New England Propeller service was super helpful and quick to get parts sent out.

edited: just to add I used a tru-tach to verify my tach was working correctly and would suggest doing the same before doing any troubleshooting.