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dnickerson46

Member
-9A with an O-360-A1A.
The plate on the top of the airbox has a cutout for the bowl drain. Is there a better way to attach the airbox top plate so the bowl drain is accessible? I attached a picture. The builder filled in all around the cutout with RTV. Is this necessary? According to Marvel Schebler, good practice is to drain the carb bowl once a year during condition inspection.

I removed the carburetor for overhaul. It's been 20 years. The vent bowl gasket failed and caused a very poorly running engine.
 

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The plate on top of the FAB isn’t elegant for sure, but it works for the most part.
The cutout is necessary to minimize the overall height of the FAB unit for cowling clearance.
RTV is cheap & easy to remove if you want access to the drain plug, a few minutes effort is all that’s needed (& a new tube of RTV).
To not seal around the carb flange is to negate the usefulness of the filter. Wise? Not so much.
 
Having worked on a couple carb'd RV's,
Not just the drain notch, but also the filter notch on the carb for the accel pump.
I have a new appreciation for my RSA-5 fuel injection servo. Flat bottom! What a concept!
Yes, just some RTV... just don't start the engine before it sets up!
 
Thanks for the input on this question. When a carburetor is overhauled, does the overhauler send both the upper and lower gaskets? There is a rubber gasket between the carburetor and the engine intake manifold and the cork gasket between the carb and the airbox.
 
I’ve had to take mine off twice. Once in March when I did my condition inspection to drain the bowl, and then again about a month ago when I sent my carb out for modification. I resealed that area both times with RTV. I tried to come up with a better solution, but nothing I tried would work. I thought rope caulk would work and it looked great when I got it on - kind of like clay if you’ve never used it. But then I thought, how would it react to gasoline? Answer - not well, it dissolves into a slimy mess. Of course, I didn’t fly with it, it was just an experiment. So, until I can come up with something better, RTV is what I will use.
 
dnickerson46 said:
Thanks for the input on this question. When a carburetor is overhauled, does the overhauler send both the upper and lower gaskets? There is a rubber gasket between the carburetor and the engine intake manifold and the cork gasket between the carb and the airbox.
Click to expand...
Mine came back with two gaskets. One for the top of the carb, and one for the bottom between the carb and the airbox top plate. I didn’t have that one on the bottom before, but since he sent me one, I used it. I also have a gasket just like the top gasket that fits between the engine and the powder coated steel cable bracket. The carb bolts on to bottom of the cable bracket with the gasket between, so there are actually two gaskets on top. This is the way my engine came to me new. I have several of those carb gaskets in my parts bin - not sure where I got them all.
 
I wouldn't slop a bunch of RTV on there - it will just create a mess. There is an infinitesimal amount of leakage around there - sealing it wont make any difference at all. I'd suggest just leave it alone a keep the installation clean.
 
71459 said:
I wouldn't slop a bunch of RTV on there - it will just create a mess. There is an infinitesimal amount of leakage around there - sealing it wont make any difference at all. I'd suggest just leave it alone a keep the installation clean.
Click to expand...
It was quite a mess and I wondered the same thing. How would sealing around the bowl drain with RTV make a difference. Yes the snorkel probably does provide some "ram air" but there are so many other places for air leakage.
 
I’m surprised no one has mentioned that Vans specifies that any gaps in this area are to be filled with “fuel tank sealant “. That certainly excludes RTV!
RTV should not be used near any fuel component.

www.vansaircraft.com

Filtered Air Box (FAB) Instructions - Van's Aircraft Total Performance RV Kit Planes

Changes made to Filtered Air Box kit for vertical induction engines. Includes new kit parts and assembly methods for improved alignment and carb heat air door changes.
www.vansaircraft.com www.vansaircraft.com
 
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71459 said:
I wouldn't slop a bunch of RTV on there - it will just create a mess. There is an infinitesimal amount of leakage around there - sealing it wont make any difference at all. I'd suggest just leave it alone a keep the installation clean.
Click to expand...
Maybe your installation exhibits “infinitesimal” air gaps (good on you for filing an accurate cut out to fit your carb!). I have worked on MANY dozens of RV’s & seen some pretty crude cutouts on some top plates. RTV is a friend here & I had never had a bad reaction in that location.
 
Thanks to everyone for the advice. I received a call from the carb shop and Dave said, "you had one of those $55M carbs." He was referring to the $55M lawsuit against Precision Airmotive for the float design. I've learned in aviation that often a small thing can lead to a big thing. In this case the bad bowl vent gasket lead to finding floats that would have failed. Another thing I've learned in diagnosing problems whether in aviation or computers. Often there is this small voice that says, "check that" even though there is not necessarily a logical reason. I can't explain it other than there some type of pattern recognition going on in our brains that we cannot explain. The moral of the story is, listen to and heed the small voice.

On a slightly different topic, what is the recommended sealant for the fuel line NPT connectors?

Is there a recommended thread lock or other suggestion for holding the star washers against the plate while the fitting the carb on to thje engine?
 
dnickerson46 said:
On a slightly different topic, what is the recommended sealant for the fuel line NPT connectors?

Is there a recommended thread lock or other suggestion for holding the star washers against the plate while the fitting the carb on to thje engine?
Click to expand...
Loctite 567.
Star washers should never seat against aluminum if that is what you mean "the plate".
PS: My rule for carb/FI overhaul is 12yrs is good, 15 you're living on the edge.
 
Walt said:
Loctite 567.
Star washers should never seat against aluminum if that is what you mean "the plate".
PS: My rule for carb/FI overhaul is 12yrs is good, 15 you're living on the edge.
Click to expand...
FYI - I found the Lycoming carburetor installation manual and it says Loctite 569 for the fuel connectors, it's probably very similar to Loctite 567. 569 is more expensive of course.
 
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