Power loss

Power loss

I have a 76 172 with a 320 E2D. On climb out at 1200' experianced a noticeable power loss. Pulled carb heat with 50 rpm loss. Did a mag check an it started running rough on the right mag. Left mag was just a little rough. After precautionary landing mag check was normal. My A&P thinks it must me carb ice. Not totally sold.

Help !!!

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Re: Power loss

I want to revise the RPM drop. The drop on pulling carb heat was 200 RPM.

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Re: Power loss

If you had carb ice, adding carb heat would improve power, but not quite back to full power.

Walter

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Re: Power loss

Joe, Here are some ideas, but really, we don't have enough information.

After pulling carb heat, you got a 200 RPM drop.  Then after turning carb heat off, did the power go back to what you expected? If it did, you had carb ice. 

If you left carb heat on, did power drop and then improve or did it stay low?  If power eventually improved to better than it was even if it didn't go back to full power (as Walter pointed out), then you had carb ice.

How about impact icing?  Was it raining or a lot of moisture in the air and cold?  Could ice have built up on the air inlet?

What were the environmental conditions? 

Overly, rich fuel mixture causing plug fowling or just loss of power?

Was your primer locked?

Has it happen again since?

Was the mixture fuel rich as it should be?

my 2 cents

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Re: Power loss

I had that happen to me on a hot day in my 172M, but I could not get it to act up on the ground either. Eventually I found it to be a bad capacitor in a throw-a-way mag. I tore down the wrong mag to start with. Did you know the key switch goes from OFF-RIGHT-LEFT-BOTH ? It is not logical, and who reads the fine print above the ignition switch?

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Re: Power loss

I had the same question regarding the OFF-Right-Left-Both non-intuitive labeling.  George Horn explained it in a previous post, which I can not locate now (figures!).  So here's what I remember and fabricate to make sense.  (I may have this backwards.)

The OFF indicates that both magnetos are grounded.  As I'm sure you know, when the Magneto is grounded it is shut off.  Right indicates that the Right Magneto is grounded, so operation is on the left Magneto.   Left indicates the left magneto is grounded so operation is on the right magneto.  BOTH indicates that that none are grounded so operation is on both magnetos.

What you think?

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Re: Power loss

RE: The power loss.

I've run into situations where I could swear I've lost power, but realized finally that the problem was that the winds aloft were causing this apparent loss in power. 

Here's the conditions when I find this happening.  I'm flying straight and level and I am downwind from a mountainous area.  There is also strong winds aloft.  I concluded that waves are formed in the air.  So that there is a vertical component to the wind.  In order to fly level I need to raise the nose and of course, with a fixed pitch prop, the engine RPMs are reduced and the speed decreases.  This appears like a power loss but the reality is different.  I am basically using the power maintain altitude.  I confirm this because suddenly I am climbing at a very high rate and end up having to cut power and dive to maintain my altitude.

Joe, you stated

"On climb out at 1200' experienced a noticeable power loss. "

Could this have happened to you?  You hit a down draft, raised the nose to try to maintain your climb rate and the rpm reduced.

Just a thought.

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Re: Power loss

when the Mag switch is on Right - then the Left mag is grounded and therefore not functioning--- when on Left - right mag is grounded and not functioning.. on both - both mags are ungrounded and operating.

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Re: Power loss

Check u'r induction for foreign object (air cleaner disintegrating or airbox seal)...check sticking valves per SB.

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Re: Power loss

Barry, Jack is absolutely right again !   With magneto switch in "right" you are checking how much rpm drop the engine has when operating on just the right magneto.  So with ignition switch in "right" the right magneto is hot while the left magneto is grounded (shut down).  And just the opposite happens with ignition switch in "left" positon.

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Re: Power loss

Bill & Jack,

Sorry for not giving you closure by acknowledging your responses.  I will differ to your understanding because I couldn't remember the convention adopted and couldn't find George's post.  It makes sense the way you explained it.  I was taking the opposite position because what I remembered about George's explanation was that it seemed counter-intuitive, but I was probably wrong.  Oh, well, I think I’m just getting old!

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