Kai, I have been working the same issue on a -9A for the past two months. This particular -9A belongs to a friend that recently purchased the aircraft. It was built with a factory new Lycoming O-320D1A and a Sensenich fixed pitch metal prop. During climb if you maintained at least 120 KTS the CHTs would quickly reach 460-475 then slowly continue to rise.
A quick inspection revealed lots of cooling baffle leaks and three intake tube gasket failures, but even after these induction and cooling air leaks were fixed the engine still ran way too hot.
The owner and I took a low altitude flight to check the temps with very little change. After leveling off at 1500 MSL I slowly leaned the engine in cruise to capture EGT and CHT data on the G3X system. I analyized the data and determined that the fuel flow peaked at only 11.8 GPH and from full rich to peak EGT was only about 45 degrees. This confirmed that the carb was way too lean!
The owner called Marvel-Schebler and talked to Mark Keeney. We were initailly going to try and rejet the carb, but Mark said that our carb was so lean and needed so much more fuel flow that more parts were required to be changed than just fuel jets. Mark recommended installing carb P/N 10-3678-32. We ended up ordering a Rebuilt 10-3678-32 from Spruce and installing it. A subsequent flight revealed much improved peak fuel flow of 13.1 GPH and somewhat cooler EGTs and CHTs, but still too lean and still too hot with a mixture spread of only 190 degrees during cruise, and running approximately 10 degrees rich of peak at full throttle.
We got in touch with Mark at MS again and asked him for some guidance. Mark researched the documentation for the rebuild of our replacement carb and said the flow bench data indicated that the carb fuel flow was set to the mid range and that it was possible to increase the fuel flow to the upper limit. So we sent the rebuilt carb back to MS and after recieving it back we flew the airplane around the pattern and now we can climb out at 80 KTS to pattern altitude without breaking 400 degrees CHT. We still need to fly a mixture flight to capture some data and see exactly where we stand, but that will have to wait until next week after installing a new audio control panel.
You may want to call Mark at Marvel-Schebler and see what he reccomends.
His contact information is:
Mark Keeney Jr.
Marvel-Schebler A/C Carburetors
125 Piedmont Ave.
Gibsonville NC 27249
[email protected]
(336)446-0002 Office
(336)446-0007 Fax
1 855-672-2272 TF