Fouled spark plugs?

[Swen]

In the Seminole when you're doing the runup and you notice one of the spark plugs (or is it a mag?) is running rough, what is the procedure to clean/fix it?

From what I can recall you lean the engine but I feel theres more to it. Help please...

[FlyingNole]

The way I learned in the single:

lean the mixture out as far as you can while the power is about runup speed, then kick up the power another 1000rpm or so for about 30 seconds, then recheck the mags.

But thats jsut how i learned it, and it seems to work

[xpanterica]

-Affected engine Throttle: 2500 RPM.
-Affected engine Mixture: Lean for RPM rise.
-Affected engine carb heat: On.
-Maintain 30 sec.
-Monitor CHT.
-Affected engine Mixture: Full FWD.
-Affected engine carb heat: Off.
-Affected engine throttle: 2000 RPM.
-Perform mag check on affected engine.

[Swen]

Thanks for the quick replies.

[kellwolf]

Just checking, but why the carb heat? Doesn't that enrichen the mixture which is why the spark plugs are fouled in the first place?

[flyguy]

What we are trying to do is heat up the engine so it will burn off the cabon deposit causing the problem, and application of carb heat helps in the process. The only reason the mixture is enrichened is because the air is being heated and becomming less dense, while the fuel flow remains constant. This is the same reason the mixture (if not properly leaned) is enrichened in a climb. But in a climb we lean the mixture to compensate, and we are doing the exact same thing when we lean the mixture in the runup.

[USMCmech]

[ QUOTE ]
Just checking, but why the carb heat? Doesn't that enrichen the mixture which is why the spark plugs are fouled in the first place?

[/ QUOTE ]


Leave the carb heat off, it dosen't help at all.


Run up the engine to 2100 RPM

Lean to peak EGT/engine roughness

Resulting high temps and mild detonation burns/shakes the lead deposites off the plugs.


FAR BETTER solution is to not foul the plugs in the first place. Lean the mixture after start VERY lean for ground ops. This way you can't take off with the mixture partially leaned.

Don't worry about detonation, at idle you can't hurt the engine. There simply isn't enough fuel available to damage anything.

[triplec76]

I just had this problem tonight. After running through the aforementioned procedure for about .4 and still having a 300 RPM drop on the right mag I decided to call it quits. At first both mags were dropping way down. After running it lean and hot for a few minutes the left mag came back up, but the right was still dropping way down and causing a backfire.

I'll be interested in seeing what the problem really was after the shop has their way with it.

[Josh]

very rare for the fouling to be a result of just lead. so the leaning isn't really needed.

more often thatn not, especially in a rental, you have a bit of oil in the cylinder, and the plug isn't hot enough (or more often isn't firing often enough because someone is trying to taxi around at 400RPM, when they should be up around 800-1000+) so it hardens and coats part of the plug.

so there is no set procedure that always works. if you lean, and it doesn't work, run up the engine full throttle, full rich. In fact, 'flood' in a little extra fuel by pumping in a manual primer if the plane has one. this will wash extra oil off the plugs before it gets a chance to partially coat a plug

anyhow, key is, you need to know why you are getting the rough running. But the idea is to burn it off.

[WindyCityPilot]

Just had this happen on my PPL checkride yesterday. The rigth mag was running very rough. I just leaned it out at 2000 RPM's until it ran rough then increased the RPM's back to 2000 for about 10-15 seconds.....then mixture full rich.....throttle back to 2000 RPM's and re-check....worked like a charm!

[triplec76]

The deal on my aircraft ended up being a fouled plug. Unfortunately, not even extreme leaning could fix it. The shop had to pull the #6 plug and clean it up (PA32R-300).

[kellwolf]

[ QUOTE ]
more often thatn not, especially in a rental, you have a bit of oil in the cylinder, and the plug isn't hot enough (or more often isn't firing often enough because someone is trying to taxi around at 400RPM, when they should be up around 800-1000+) so it hardens and coats part of the plug.

[/ QUOTE ]

Add the low RPM with people that don't lean the mixture for taxi, and it's a textbook plug fouling situation. I actually have a "Spark plug cleaning" checklist with my Seminole stuff for this since I guess a lot of the time builders here tend to run full rich 24/7. Density altitude here is more or less above 3,000 on the ground from like 9 AM to 8 PM, so not leaning does a number on the plugs. I'd just never heard of using carb heat to help clean the plugs before.....