Idle / Mixture adjustment with new PMags

Hello all,

Just installed 2xPMAGs last weekend. O-360 fixed pitch. Install went fine, and the motor starts instantly. Idle runs very smooth. CHTs on 3/4 are now much higher which I will attack in a different thread after reading older posts. What I did notice is an overall increase in RPM at the normal throttle positions with my fixed pitch prop. I was hitting 2600 rpm level with half throttle deflection at 1,000ft, and my ground idle is right around 850-900 which seems high. I’m thinking that I need to reduce this a bit. Any thoughts? How do I do that without cutting out top end throw deflection of full power? Is the adjustment made on the throttle side or on the carb side? What about mixture adjustment to go along with this?

Thanks for the input all!
Wingnut

Our O-360 has a single P-Mag and a Slick 4371. It happily idles at 600RPM, thanks to the P-Mag.

I'm not sure I fully understand your question re throttle adjustment. Most common advice given is to adjust the linkage such that full throw of the throttle arm on the carb is achieved with only slightly less than full travel of the throttle knob. Or, in other words, when you firewall the throttle it should to to the firewall, minus perhaps 1/8" of "cushion". This 1/8" cushion is needed to ensure you will always be driving the throttle arm fully to its stop, even as the throttle cable moves through the full range of expansion and contraction associated with hot and cold temperatures.

Same goes for idle - the throttle arm should move fully to the idle stop and you should still have some movement left in the throttle cable so you'll always be able to get the throttle arm fully against the idle stop, even with adjusting that idle stop, and with the cable being exposed to its full range of thermal expansion and contraction.

If you have excess cable actuation travel, adjust the cable so it is 1/8 or 3/16" from its fully "in" or "firewalled" position when the carb throttle arm is at its full throttle stop. That way any excess cable actuation travel will become invisible to you since you won't pull the throttle out any further than the idle stop.

Regardless of how you configured your P-mags (E-mag is the company), at idle they move the timing to 19.6? BTDC. This allows you to get a really low idle.

If you haven't configured your P-mags properly, then you will have higher CHT's. I have configured my P-mags with a -1.4? offset and my CHT's went down and my speed went up.

If you haven't already done so, watch the talk I gave on Ignition Basics. It is worth the time. After watching it, feel free to give me a call.