Hi
I'm running in my overhauled engine - 4 hrs - all a full rich.

Today I landed at a nearby airport and when I did the run-up to return
home the left mag gave a 400 rpm drop. I tried it again and got another
400 pm drop.
Third time I tried it I had no left mag at all - drop to cut-off - same
4th time.

Shut down - check all connections - everything looked good - no loose
wires etc.

Today for the first time I used my new carb-temp guage and as it was
reading 30F I added a small amout of carb heat to bring it to 37F. On
reflection I should have leaned slightly to allow for the extra richness
from the cab heat but I didn't.
I went back to the aircraft and it stated OK. I ran it leaned for a
couple of minutes, went full rich to 1700 rpm and did mag checks - both
were good. I did it 5 times, and departed for home. Aircraft ran great,
after landing I did 3 more mag checks and they were all good.

Question - Could fouling really have totally shut down my left mag?

Thanks for reading,

Tony
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Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE