RPM not reaching 2700

[isaacpr7]

For some reason I have not been able to get 2700 RPM on take off since last annual was completed. Since that annual I have replaced all spark plugs, overhauled/timed both mags, and replaced the intake air filter. Fuel pressure is 6 psi. Nothing has given me an RPM greater than 2500-2600 RPM. I checked prop and throttle cables to ensure they have full travel by visually inspecting that each full position hits the stops. I removed the foam air filter for testing and it gave me 2550 RPM which is better than the 2500 RPM I've been getting today.

Any thoughts?

[Guest]

Tachometer accuracy check first to verify the rpm is actually low.

Clarence

[bonal]

Tachometer accuracy check first to verify the rpm is actually low.

Clarence

+1 after you confirm you are not getting max 2700 then adjust prop governor this might take a few attempts. Mine did the same thing after its last annual don't know why. First attempt got it right back

[isaacpr7]

I checked that with a tach tester and the tester reads about 20 RPM higher than the instrument at 1000 RPM. I can't recall what the tester read at full throttle but I will check again. I belive that it was a higher spread at full throttle.

[isaacpr7]

+1 after you confirm you are not getting max 2700 then adjust prop governor this might take a few attempts. Mine did the same thing after its last annual don't know why. First attempt got it right back

Thanks bonal. Adjusting the governor was my IA's first thought. I will try that next time he comes over. I checked that the control hit both stops while moving the cable to both ends and it was getting full teavel. Like you said, it's possible that adjusting the control stop will fix the problem. I wish there was more space back there to fit my hands though. Lol!

[bonal]

My tach reads about 100 high at max rpm but is accurate below 2400 used an optical tach on a flight and noted all rpm through the range. Like most things vintage always some trial and error good luck

[RobertGary1]

It can legally read off but you are required to placard the error.

-Robert

[mike20papa]

What are the mag checks like?  Same as before?  Start up & idle?  Try the mag checks at an overly lean mixture, so that rpm is limited by mixture, then mag check again.  You will get more like a 100 to 150rpm drop each mag.  This lean run-up method is reported to be more telling of mag, plug, plug wire problems.  Good luck!

[isaacpr7]

Found a good read on governor adjustment:

http://www.mccauley.textron.com/pga_governors.html

[bonal]

It can legally read off but you are required to placard the error.

-Robert

Will check it again and placard the variations

[isaacpr7]

After reading a couple of publications and articles I learned that the static RPM is about 100 low from when you go airborne on take off. After taking it for a test flight it checked out okay just under 2700 on the tach but the difference was accounted for by the result while using the optical scanner.

[Tommy]

First thing is to make sure your tach is reading correctly. So an optical tachometer is required.

One you have determined your tach is reading correctly, adjust your governor. It could just be a simple two anticlockwise turns of the limiting screw or you may well have to adjust the control cable too.

[Guitarmaster]

One thing I learned from Cody Stallings is that the prop can get hard oil in the hub and not allow the prop to reach the low pitch limit. When was the last overhaul of the prop?

[Cody Stallings]

Guitarmaster is correct. The oil in the piston will centrifuge overtime an create a grey funky pudy like compound. It will at some point buildup to a point to where it becomes a mechanical stop.

[isaacpr7]

Thanks for the replies guys. My issue has been resolved. I just needed to do the test after takeoff and it checked out okay as confirmed by the optical reader as well.