I took the day off work today, and spent the morning at the hangar. I had noted yesterday that the idle mixture was very rich. At 700 rpm, if you pull the mixture back very slowly from full rich, the rpm should increase 10 to 50 rpm. I had over a 200 rpm increase. I wasn’t sure whether this was simply way out of adjustment, or whether it was a symptom of some other issue. The idle mixture should have been set during the engine run in the test cell after the overhaul, so I wanted to be sure that there wasn’t something else going on. A web search indicated that a rich idle mixture could be caused by an internal leak inside the fuel injection servo. Such a leak, if present, could be seen by removing the air induction “snorkel”, and putting a cap on the metered fuel line going from the fuel injection servo to the “spider” on top of the engine. Then you select full throttle and rich mixture, and pressurize the system with the boost pump. An internal leak will cause fuel to come out of the small tubes that can be seen in the throat of the fuel injection servo. There was no leak in my system.

Another possible cause of too rich mixture could be too much oil on the K&N air filter. So, I put the induction snorkel back in place without the air filter for a quick test. I still got more than a 200 rpm rise when I pulled the mixture back at 700 rpm, so the air filter was not the cause. After putting the air filter back in place, I adjusted the idle mixture and idle speed to be approximately correct. As a point of reference, I needed to turn the adjusting wheel about one full turn to get the mixture approximately in the right range. I’ll do the final adjustment after the engine is broken in.

I chased down two small brake system leaks in the cockpit, and spent quite a while looking for, but failed to find, the source of a fuel smell in the cockpit.

I’ve got some sort of problem with the activation of the fuel flow option on the EIS 4000 engine monitor. You need to enter two codes to activate that option, but my system refuses to accept the codes. I couldn’t raise GRT on the phone, so sent an e-mail.

This afternoon I did some sanding on the transition ducts I made to connect the cowl air inlets to the plenum chamber on top of the engine, then applied some more fibreglas filler.