Hey Guys,
Just a short follow up on the stuck throttle I experienced last week. I did
remove the entire throttle cable and took it apart. there was some oily residue
inside but I could not find anything that screamed trouble. I ordered a new
throttle cable and installed it any way. When i installed the throttle cable I
removed the Aerocarb and disassembled it. I did find a problem there. It
really was not apparent until looking very closely but there was a build up of
some kind on the out flow side of the slide and venturi. I first noticed it on
the very edge of the venturi circle behind the slide. There was a layer of
translucent brown of maybe 3 or 4 thousandths thick. It came off in pieces as
if it were brittle but had somewhat of a tack to the surface. Lass than a post
it note sticky. After removing the slide I found that there was some build up
on the back side and it also showed signs of impulse waves in the build up. The
build up was also the size of the venturi circle indicating that it had to have
formed there while at idle or with the throttle closed. The material broke down
and cleaned off with brake clean very easily and left everything like new.
There was no sign of anything on the intake air side of the slide, all
perfectly clean.
The factors that i can think of are the following.
I have used Marvell mystery oil for the past 200 hours
i had to put 10 gal of 93 oct. Sunoco in to get home from the
Gathering- There was about 6 gal of av gas in the tank. I flew about 3 hours on
this mixture. It did ruin the O rings on the fuel tank caps
I do have a oil leak that gets into the air intake but does not
seem like enough to do any thing ( I put in about 1 qt in 35 hours)
Any thoughts on what might have caused the problem. I have about 550 hours on
the carb and never any sign of dirt before. It did not seem to run any
different on the auto fuel that I could tell. Exhaust temps were ever so
slightly lower. I did run carb heat for maybe an hour of the flying in very wet
conditions and that is unfiltered air, but only partial use of the heat, with
the carb throat temp I can use the it to my liking and I had it set at about 80
deg. which was only about a quarter open. The coating was nothing like the
glazing that we used to see on auto carbs that it took an act of God to get
cleaned off.
Joe Horton,
Coopersburg, Pa.
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