Rising MP when lowering RPM

[damcmurt]

Hello,

I am new to the site and recently purchased an '80 231. On occassion when I am leveling off from a climb and dialing the RPM down to 24 I have seen the MP rise to over 37" when I have it set at 33" in the climb. My understanding is it should drop maybe an inch as you lower your RPM.

I have also noticed that it may wonder up and down an inch or 2 after I have it set and the friction lock set.

I would love any ideas...

Excited to be flying a mooney

David

[DonMuncy]

My 231 is hard to adjust to a particular MP as well.  You set it at one setting and it will move shortly thereafter. Sort of like "chasing" a needle in a crosswind. I have always thought it was the nature of the beast.

But I have never had the MP go up with a reduciton in RPM. It is virtually always the opposite.

Don

[DonMuncy]

My 231 is hard to adjust to a particular MP as well.  You set it at one setting and it will move shortly thereafter. Sort of like "chasing" a needle in a crosswind. I have always thought it was the nature of the beast.

But I have never had the MP go up with a reduciton in RPM. It is virtually always the opposite.

Don

[N9937c]

Are you letting the plane speed up to ~cruise speed before setting the mp and rpm for cruise?

This increase in spped will change all your settings as well as leaning.

larry

[jlunseth]

Yes, I agree, you need to let the plane settle down after you level off.  The speed will go up, among other things.  If you are climbing 120 KIAS your cruise will be 20+ knots faster, and that will increase the ram air effect from the intake.  I normally will level off and throttle back to the setting I want to be at, say 31", but then will let the plane speed up and stabilize before doing a final cruise setting.  The increase in MP that you mention does seem alot though.  An inch or two would not surprise me. 

[damcmurt]

Thanks for the input. Flew today and we messed with the friction lock. It seemed to be more stable but had a low ceiling so I didn't get it up that high, still need my IFR ticket. Going to find out if I can just replace the friction lock or if I have to replace the whole cable. Due in the shop soon for the oil change so we see what the shop thinks.

Let you know what I find

Again Thanks

David Mc