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mayo3808

Well Known Member
Hi all completed my first flight this weekend everything went ok. I have a problem and need your help. RV-9A,0-320-E2D, with AFS 3500 EE. The engine starts good, idles good, mag checks good and smooth @ 1500RPM. takeoff climb is smooth, #3 cylinder temp was a little high about 430 but comes down after leveling off to below 400. I glassed the opening of the inlets today will see how this does. But heres the problem when I level off and pull throttle back to 2400 or 2500 RPM the engine surges about 10 RPM according to the engine monitor tach. You can here and feel it at all RPM.
It does it at lower RPM as well, just slower surging. Boost pump has no effect, switching tanks has no effect. I have replaced the carb gaskets used a little RTV on them, removed oil seperator, checked all fittings for leaks, see no leak on engine(fuel or oil), timing @ 25 BTDC. I do believe it is fuel related just not sure what. I will talk with Bart tomorrow and get his help. I may have forgot some details as i write all this and I have flown it three times now and it does the same thing every time. I forgot running three blade catto prop. Any idles? Thanks.
 
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first flight

Sorry I don't have a fix for your problem with the surging RPM's but I did want to congratulate you and the plane on your first flight together!
 
Congrats on your first flight!

I'm assuming from your post that you're using a fixed pitch prop? What type of prop?

mayo3808 said:
I have replaced the carb gaskets used a little RTV on them
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It is generally a bad idea to use RTV where fuel will touch it. The fuel will soften and loosen RTV which could lead to a day ruiner. :)
 
If his three blade Catto is anything like mine, it doesn't have a governor:)

And I don't have a clue as to why it would surge. An intake leak that would cause that would usually cause idle problems. Congrats on the first flight! Be careful, but a few hours break in might help.

Bob Kelly
 
Carb heat seems to make it worse. As I can tell the air filter and air box is installed ok. But I do see carb temp running normal until I pull power back for landing then I cans from 78 to 135. And I did not pull carb heat. Not sure whats going on here. Thanks
 
Radiation !

When you pul back for landing, there is less air going through the carb, so less cooling from the inside, but your exhaust pipes are still radiating a lot of heat towards the carb. That is probably why the carb heats up a little.

I am installing a heat shield between the cross-over pipes and the Throtle body and have mufflers on the exhausts, with air cooled shrouds, so that protects the throtle body from radiant heat. The shields also keep the fuel lines cool(er).

Regards, Tonny.
 
Jamie said:
It is generally a bad idea to use RTV where fuel will touch it. The fuel will soften and loosen RTV which could lead to a day ruiner. :)
Click to expand...

It's a bad idea to use RTV on a carb gasket in your jalopy. It's a horrible, potentially lethal idea to use RTV on a carb gasket in your airplane.

Just my opinion Brent, but you should get that RTV time bomb out of your carburetor before it kills you. :eek:
 
Carburetor float sticking?

I am not an expert and have never had one of these carbs apart, but I would expect either a sticking float or float valve to cause some surging as the changing float level caused the mixture to vary. It sounds like you will have the carb apart again to clean out the RTV, so it should be easy to check the float and float valve.

Good luck, and congratulations on a successful first flight.

John
 
Talked with Bart (Aerosport) today and he is sending me a new carb today. But whats the problem with RTV on the carb to intake gasket. I am talking about very little, just enough to hold in place while the carb is installed ? Thanks:confused:
 
mayo3808 said:
Talked with Bart (Aerosport) today and he is sending me a new carb today. But whats the problem with RTV on the carb to intake gasket. I am talking about very little, just enough to hold in place while the carb is installed ? Thanks:confused:
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Brent,

The deal is the gasket seals the carb to the throttle bracket and the throttle bracket to the sump. If you use RTV, even a little amount, the fuel will eventually deteriorate it, thus allowing air into the intake system.

When you swap out your carb, buy two gaskets and install those ?dry?.
 
mayo3808 said:
Talked with Bart (Aerosport) today and he is sending me a new carb today. But whats the problem with RTV on the carb to intake gasket. I am talking about very little, just enough to hold in place while the carb is installed ? Thanks:confused:
Click to expand...

The carb to intake gasket is perhaps the least worst carburetor location to have RTV. As Bill mentions, all that can happen is that it will eventually create an air leak, causing your engine to run lean and backfire. ;)

Your original post mentioned "carb gaskets". I'm glad to hear it wasn't a carb tear down and re-assemble with RTV smeared over everything.

The advice remains: keep RTV away from carburetors.
 
Brent,

One other thing, check the bolts that hold the carb on and the intake and exhaust nuts for proper torque.

After a few heat cycles (hours) they should be checked. (This per Lycoming.)
 
Great Aerosport service

Yeah, it sounds like something is funky with the carb, especially if the 10 rpm surge is occuring as you pull the power back. Keep us posted as to what happens when you put the new carb on. Congrats on the plane.
 
Sounds like a sinking float to me. I had one in an -6a do almost exactly what you describe. Almost died on rollout too :/.

The RTV discussion is correct. There are mighty few places on an airplane where RTV is the ideal solution, but the good news is, most of the usages won't cause damage to your engine, just corrosion on the airframe and such. Gaskets are not one of those. You can use Fuel Lube, or NON RTV gasket maker on carb gasket if you want. There should be absolutely NO need to stack gaskets either...
 
UPDATE

Replaced carb with new one from Bart engine surge gone. Engine is nice and smooth. Looks like i may need to drill the main jet, EGT are high. I will check the diam of the jet first.:D
 
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