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pmag power question

R

rwarre

Well Known Member
I am experiencing a slight power loss with the 1 pmag/1 slick mag combo.
Have checked timing on the slick and the pmag. Slick is at 25 degrees BTC and pmag set at TDC. I was able to see 150 ktas with two slick mags, now I am only able to get 146 ktas after testing for a couple of hours. I am running full power. I checked rpm drop in flight and got an 80 drop on the slick and a 50 drop on the pmag. Trying to understand the timing advance with the pmag but not sure if that is my problem. What other tests or factors should I be thinking about?
 
Toobuilder said:
Are you running the "A" or "B" advance curve on the Pmag? How is the MP tube attached?
Click to expand...

The "A" curve is what you should be running and requires a jumper between pins 2 and 3.

Also confirm that all your plug wires are seated properly.

Did you check the plug gaps before installing them?

Do you have a restrictor in the MAP line to smooth out the pulses?
 
pmag

Have checked that plug wires are firm and seated properly.
Plugs were gapped at .030 prior to installation.
Manifold pressure is taken from number 2 cylinder primer port. The only place that was possible to get a fitting. I had a primer line on that port and just used same tube line but cut, for the mp
 
Map restrictor

MADE A MISTAKE ON SIZE PULSATION-DAPANING SNUBBER. ORFICE ."004"
I believe I have a spare 1/8 male/ female restrictor ".020" from McMaster Carr. Will be at airport shortly to check. Sells for about $9 Will ship for $8. If interested text me at 714-501-1310
 
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rwarre said:
Using A curve
No restrictor on MP
Click to expand...

It is possible that your timing is bouncing around with the MAP. Any chance you can put a restrictor in and report back?

The fitting mentioned above, a lawnmower fuel filter, or a drilled rivet should work.
 
fixed

I installed a rivet with a .025 hold drilled in it. Seems to have fixed the problem. The power is back to more than with two slick mags. Now I just have to get used to flying with EI.
 
That's good news!
At your next condition inspection, I recommend you open the plug gaps up to .032. (The range is .030 to .035.)

The larger the gap, the easier it can ignite leaner mixtures.
 
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GalinHdz said:
How do you install a lawnmower fuel filter to do the damping? Aren't they one way devices or does it matter?

:cool:
Click to expand...

Good question, I have never used one. My preference was to drill the smallest hole I could in an AN470-4 rivet and capture it in an AN fitting upstream of the MAP sensor and P-mags. It won't deteriorate like a filter will.
 
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how small

I drilled a .025 hole in my mp line for my restrictor. Is that too small. How would the size of the hole affect the pmag operation?
 
In this case size doesn't matter, smaller is better. You are restricting pressure, not volume.

The MAP is not a steady pressure, it bounces up and down, positive and negative. So, depending upon when each ignition samples the MAP, they could get different values. Thus, different timing.

The restrictor smoothes out the pulses so the P-mags should read the same values.

Please let us know how it works out.
 
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mag drop

How much rpm drop do you get with Pmags? With Emag I would think it minimal. Oh and at what RPM?
 
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