> >On a different note, many Marvel carbs with the one piece > venturi do tent to > >run lean under cruise conditions. Precision has a fix, > which I believe > >they are still providing free. > > John, > > Isn't the Marvel carb the one with the mixture control wired > to full rich? > Or is that the Stromberg? Don't remember, except mine is > wired full rich. > > What is the "Precision" fix? Should it be shared with the list? > > Pete >
The Stromberg Carb is the one whth the mixture generally wired full rich. This is because the adjustment is very touchie and student pilots would pull it out in cruise and kill the engine. Also, with the average age of these carbs, most of them don't work well anyhow. The Marvel carb is the newer design with the mixture control that is capable of shutting the engine down at idle (The Stromberg mixture control is ineffective at low power settings). There is a recent AD requiring (more recently modified to not require) changing the venturi in the Marvel (now Precision) carb from a two piece unit to a one piece unit. There were a lot of lean cruise problems in small Continentals attributed to the new venturi. Precision was giving away new mixture tubes that compensated for the problem and may still be. More recently, the AD was modified to allow use of the old venturi with a recuring inspection. The old venturi is problematic, and IMHO the desirable situation is a one piece venturi and a mixture tube that results in the correct cruise mixture. A good overhaul shop should be able to test the fuel delivery rates and verify the carb works correctly. Clear as mud, right? John
<<attachment: winmail.dat>>
