Blew air through the vent, flows fine. I can suck air back out of the tank but it's really slow. Ended up pulling the check valve out and it looks fine.
O-470 is carbureted. Just flew to lake tahoe and now it's running rich enough that it's running rough. Pull the mixture out excessively and it runs great. I think that tells me it's the carb.
Ran fine before the annual. Just had the plug rechecked today and they also pressure and resistance tested the plugs. The mechanic said the idle mixture wasn't adjusted right but I'm not sure if that could be a problem or not.
Pressurized the induction system and didn't find any leaks. Didn't find anything in the carb either. Seems to come and go but gets fairly consistent at altitude.
Induction leak could explain it. All rubbers were new about 200 hours ago.
Everything to do with the mixture control is right.
I can still repeat the problem at 23" at lower altitude.
3 hours after it was annualed. Plugs are good, 1600 tt, probably 25 years in the engine. Borescope has been done, verything looks great. I found a little junk in the fuel screen on the carb but not enough to cause a problem.