Brief Description: Replacement fuel servo mixture lever
I've noticed that the fuel flow on takeoff and climb out are lower than they should be. This is partly due to the fact that the fuel flow transducer isn't fully calibrated yet, but I also noticed that the mixture lever on the fuel servo was limited by the travel of the mixture cable. It would hit the idle cut-off stop but there was approximately .040" gap between the mixture control and the full rich stop. To correct this problem, I decided to make a shorter lever arm which would provide more rotational travel of the servo mixture control for the same amount of mixture cable travel. I had the same issue with the throttle control prior to first flight and to fix that I purchased a shorter lever from Avistar, the manufacturer of my servo.
For the mixture I decided to modify the old throttle lever that I had replaced for the shorter one. The original mixture lever had a 1 5/8-inch center to center dimension between holes and I calculated that it should be approximately 1 1/2 inches in order to get the full 70-degree travel of the mixture control. The old throttle lever was 2 inches center to center so I decided to drill a new #12 hole at 1 1/2 inches and trim the excess. It's a bit different from the original mixture lever in that it has a joggle to move the cable mounting surface out about 1 inch whereas the original mixture lever is straight but I determined that it would work if I mounted the cable rod end to the inside surface rather than the outside.
Today I drilled the new #12 hole using my drill press. I started with a #30 hole which I opened up to #14 and finished off with a #12 reamer. I then used a cutoff wheel in a dremel tool to trim the lever 1/8 inch from the new hole and rounded the cut end with a bench grinder.
I replaced the old lever with the new modified one, hooked up the mixture cable to the inside and after makining some adjustments to the cable position the mixture now moves through its full specified travel.
Drilling the new hole for the mixture cable attachment
