If you leave the mixture lean while you do your run up, the RPM will drop more than if you have a rich mixture. I do my run up lean. You might want to consider Iridium plugs. More fire, bigger gap. The price of the Iridium plugs has come down from $74 to $35.
The run up is not the place to fully check the mags. A high RPM run up is just the place to chop up the prop. While in cruise flight, try the left and right mags. This really tells the tail.
If the RPM drop is greater on the left mag, you should determine the problem and correct it. The problem could be the mag and/or its points, the wires or the plugs. If the mags are Slick 4200's they should be changed at 700 hours. If they are Slick 4300's they should be inspected and the points changed every 500 hours.
I have switched to Cleveland wheels but with my Matco's I could always lock the wheels whenever I wanted to.
Date: January 14, 2008 12:46:58 PM GMT-05:00
Running an 0-32O with 2 mags-frequently get a 200 RPM (or sometimes greater) drop with roughness on the left Mag when doing run ups.
Until recently I had the MATCO brakes installed I was unable to run up much past 2000 RPM without creeping forward and thus the problem was hard to clear. On applying full power for take off-the engine runs a little rough for a couple of seconds then runs smooth.
Obviously the cause is fouling-anyone care to add comments or similar experiences?
I always taxi with mixture leaned out to the max but mechanics can be more careless when picking up aircraft for maintenance.
What are your thoughts?
-- Lorn H. 'Feathers' Olsen, MAA, ASMEL, ASES, Comm, Inst LNC2, FB90/92, O-320-D1F, 1,300 hrs, N31161, Y47, SE Michigan
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