Excessive Mag drop during Runup

by Ron Parr in 912 / 914 Technical Questions 11 years ago

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Re: Excessive Mag drop during Runup

by bill martin » 11 years ago

bill martin

10 757 0

Fredy,

Kind of difficult to really fine tune without an EGT but there is one thing you can do.

If the engine is running OK, take a short flight for twenty minutes or so. When you land, don't taxi or idle, just immediately shut down the engine and pull a plug on each side. If the plug insulator is clean and white or light brown, you are probably OK. If the insulators and tips are sooty black, you may be too rich. If you let the engine idle a while before pulling the plugs, they will usually be black even in a properly tuned engine.

Bill.

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Re: Excessive Mag drop during Runup

by Roger Lee » 11 years ago

Roger Lee

125 5.12k 4.53k

Hi Fredy,

I'm with Bill. It's good to have EGT's. They are easy to install and are more helpful than some other instruments. At least put an EGT on cylinders #3 & #4.' Most likely you are fine at your current needle position, but if you are taking off at 6'K and fly up around 9'K-10'k all the time moving from the #3 needle position to the #2 won't hurt, but take the time to install the EGT's. It easy enough to do and worth while. Once in the #2 position you would then need to watch the temps when flying back down around sea level.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Excessive Mag drop during Runup

by FEDERICO COMPEAN » 11 years ago

FEDERICO COMPEAN

5 9 0

Thanks a lot guys........ I think I will go with the installing the EGT before doing as Bill suggests. I don't feel too comfortable with the idea of pulling the spark plug out on a hot engine, nor am I sure I would be able to recognize the colors difference.

What temperature would indicate needing to bring the needle down from #3 needle position to #2? (thanks from the top down correct?

Thanks again.

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Re: Excessive Mag drop during Runup

by bill martin » 11 years ago

bill martin

10 757 0

Fredy,

It's OK to let the engine cool before removing the plugs. Just don't let the engine idle very long after landing. The color difference will be quite obvious. On a rich engine, the plugs will be smooth velvety jet black all over. A proper mixture will leave the plugs with light brown or tan color on the insulator with dark but clean tips.

The reason for not idling for long periods before removing the plugs is that engine will normally run a little rich during idle and it only takes a few minutes of this to blacken the plugs. This is not a problem because this carbon burns away soon after throttling up.

An extremely rich mix will cause rough running and the plugs will often be wet and black. An extremely lean mix will, at best, cause the plug insulators to be a bright chalky white. At worst, an extremely lean mix will burn valves, melt pistons, and other nasty stuff.

Murphy's law states that an engine runs best just before it melts. You really should get an EGT gauge. With the gauge, you can fine tune the mix so that you are a little below the recommended upper temp limit at WOT.

At your higher altitude, you may be running a tiny bit rich but probably not enough to worry about if the engine is running OK. Give the plugs a look and tell us what you see.

Bill

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Excessive Mag drop during Runup

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