Bad Mag Check

150's are notorious for fouling plugs. The o-200 continental was not designed for the 100LL. 100LL has 4 times the lead content than 80-87 (which is what the 0-200 was originally certified for) which is why they are prone to fouling. When on the ground you have to keep the mixture as lean as possible, and even in the air if your below an altitude that you would normally not lean it, you will need to as well.

Many times "burning it off" just will not work. Sometimes you just have to pull the plugs and clean them!

DO NOT fly it if it's dropping more than it should. Some people think its no big deal that it will clean up as the engine runs at high rpm in flight. I had two friends die in a C150 that was very prone to plug fouling. from the eyewitness accounts of the accident it sounds like they tried the burn it off routine and crashed after take off. there appeared to be a partial loss of power.
 
Crism said:
Rough mag checks aren't uncommon in the 150 with the Continental O-200. Depending on the severity of the drop, I'll usually increase the RPM to about 2100RPM, lean out the mixture as you would during cruise (until RPM drop), and leave it there for about 15-30 seconds. Mixture forward, 1700RPM, mag check again. If it doesnt clear, at that point I'd usually go full throttle, lean it again, and leave it there for a good amount of time 45-60sec.

Typically I don't go full throttle in an attempt to save wear and tear on the prop. But it's there if you need to. One other thing you might try to do is perform a run-up with a lean mixture just to see if that works.

After the 2nd or 3rd attempt at a mag check though, I'm bringing it back to the ramp.
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This.

When I was earning my PPL I had to do this on both of the 152s I was training in on almost every flight until both planes got new mags at their annual. The 30-40 second burnoff procedure always worked for us, though. I just assumed that everyone had to do this all the time.

It wasn't until I moved to Austin and started flying nicer airplanes that I discovered that this was not the norm for most people.
 
Crism said:
Rough mag checks aren't uncommon in the 150 with the Continental O-200. Depending on the severity of the drop, I'll usually increase the RPM to about 2100RPM, lean out the mixture as you would during cruise (until RPM drop), and leave it there for about 15-30 seconds. Mixture forward, 1700RPM, mag check again. If it doesnt clear, at that point I'd usually go full throttle, lean it again, and leave it there for a good amount of time 45-60sec.

Typically I don't go full throttle in an attempt to save wear and tear on the prop. But it's there if you need to. One other thing you might try to do is perform a run-up with a lean mixture just to see if that works.

After the 2nd or 3rd attempt at a mag check though, I'm bringing it back to the ramp.
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We do this too, for our 150 back home. This saved my buns when I was in Juneau by myself, thinking I would have to take it into the shop there and stay a couple days.
 
On our 172's all we have to do is run the engine at full power for 5-10 seconds and it will clean off the spark plugs. If the full power doesn't work we put it to fool power and then lean the mixture for 5-10 seconds. That has taken care of the problem every time.
 
BaronPete,

Don't let your instructor irritate you like that. You made a sound decision based on your experience and knowledge. You're safe, the plane's safe, and you'll get to fly another day.

Never feel put out/irritated/disappointed/guilty about any decision you make that leads to the same outcome...you're on the right track
 
BaronPete said:
I taxied back in and called my instructor out (he was aggravated) and he leaned the mixture a bit, did the runup, waited a bit, then rapidly went through the mag check and all seemed well.
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He shouldn't have been aggravated. When my students are PIC, I want them to adhere to 91.13 (careless and reckless operation). This is kind of a catch-all regulation. Would it have been careless and reckless for you to takeoff in this situation? Yes! If you takeoff when you are 99% sure the flight will be completed safely, you are being careless and reckless!

You made the right decision, don't feel bad about it.
 
Pulling the plugs periodically and cleaning them BEFORE they start to foul can save you the aggravation of canceled flights. It's generally the lower plugs and they are often lead-fouled. That is, the lead from the fuel accumulates inside the plug. No amount of leaning and revving the engine will clear this out. Pull the plugs, sandblast them clean, use compressed air to clean all sand from the plugs and the threads, put a small amount of anti-seize on the plug threads, use a new copper gasket (or anneal the old one) and torque the plugs according to the manual using a torque wrench.
Leaning and revving can clean plugs which are gas fouled (from running to rich).
And don't over-tighten the plug leads!
 
Here's a question for the MX guys too...

A common habit for me when I'm shutting the engine down is to throttle it up to about 1000-1200RPM so it's running smooth, then cut the mixture. I don't like to cut the mixture on an engine that was sitting there coughing or not running smoothly. The way I see is, if it's burning smoothly when I pull the mixture, it will shut down smoothly, and theoretically there should be less deposits of carbon/lead/fuel/etc left over afterwards for the next poor soul who has to start it.

Is there truth behind this at all?
 
Maurus said:
On our 172's all we have to do is run the engine at full power for 5-10 seconds and it will clean off the spark plugs. If the full power doesn't work we put it to fool power and then lean the mixture for 5-10 seconds. That has taken care of the problem every time.
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I'm curious, because my instructors never taught me how to get a 172 all the way up to "fool" power. ;). Is there a little red button perhaps?
 
Crism said:
Here's a question for the MX guys too...

A common habit for me when I'm shutting the engine down is to throttle it up to about 1000-1200RPM so it's running smooth, then cut the mixture. I don't like to cut the mixture on an engine that was sitting there coughing or not running smoothly. The way I see is, if it's burning smoothly when I pull the mixture, it will shut down smoothly, and theoretically there should be less deposits of carbon/lead/fuel/etc left over afterwards for the next poor soul who has to start it.

Is there truth behind this at all?
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At my old flight school that I mx apprenticed at this drove us all nuts, because some of our students would take it to the extreme and throttle up to like 2000 RPM and sandblast the ramp every time they shut down. Nobody I worked with had a definite answer.

My CFI was also against it, but your argument seems logical on the surface and I too would like to know the answer to this.

To the OP: You're going to lean the mixture for taxi EVERY TIME now right? Don't be "that guy" that everyone else curses under their breath when they get the plane after you. Don't forget to re-lean as part of your after landing checklist. :)
 
NEVER feel bad about not flying an airplane you're not comfortable in, especially so while you're training.

Amongst a million other obvious reasons, the rest of the flight you will be constantly thinking about that Mag issue.

Even IF you are not sure how to solve a problem and feel that you should, looking a little foolish is better then being a lot dead!

Good call IMO.
 
I appreciate all the responses.

And yes, I made a new checklist tonight with lean mixture in the start up procedures ;)
 
Crism said:
Here's a question for the MX guys too...

A common habit for me when I'm shutting the engine down is to throttle it up to about 1000-1200RPM so it's running smooth, then cut the mixture. I don't like to cut the mixture on an engine that was sitting there coughing or not running smoothly. The way I see is, if it's burning smoothly when I pull the mixture, it will shut down smoothly, and theoretically there should be less deposits of carbon/lead/fuel/etc left over afterwards for the next poor soul who has to start it.

Is there truth behind this at all?
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lycoming had a service bulletin out that had instructions for shut down that said to run engine at 1200rpm for 1 minute. this was to help clear the plugs before shut down. This was for lycoming engine that had been certified on 80-87 fuel.
They had a later SB which I cannot find now that said to run at 1200rpm for 10 seconds Prior to shutdown (engines not certified on 80-87) so yes there is some truth to it.
 
mooneyguy said:
lycoming had a service bulletin out that had instructions for shut down that said to run engine at 1200rpm for 1 minute. this was to help clear the plugs before shut down. This was for lycoming engine that had been certified on 80-87 fuel.
They had a later SB which I cannot find now that said to run at 1200rpm for 10 seconds Prior to shutdown (engines not certified on 80-87) so yes there is some truth to it.
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oops could not edit. it was not 1200rpm, that was a typo, but the later SB was L192 which suggested running the engine between 1000-1200 rpm after landing until engine temp stabilized. prior to shut down run the engine at 1800 rpm for 10 seconds then return to 1000-1200 rpm and immediately shut down shutdown...again, yes there is truth to it.
 
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