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Fuel Spraying From Muffler (OS MAX AX 46)

#1
Hey all, I bought an old nitro plane from a gentleman at my airfield a couple years back and am just getting around to making it airworthy again. I ran a full tank through the engine today at a lower rpm, but when I raised the throttle, fuel would "splatter/spray" from the muffler, and I'm not sure why. I'm using a 15% fuel, and I tried leaning it out, but the engine really didn't seem to appreciate that. Any tips?
 

Merv

Well-known member
#2
A small amount of fuel coming out of the muffler is what you want. If you hold your hand in the exhaust for a few seconds, it should feel oily. If it’s slimly, that’s too much.

Every glow engine I owned would eventually get a coat of varnish. When varnished, the engine would only run fat (rich). When you leaned it out they would over heat and cut out.

The solution, boil it in antifreeze to clean it. Get the kind that is safe for aluminum, mix it 50/50 with water. Use an old crock pot or fondue pot. Remove the carburetor, muffler and glow plug. Rotate the engine so the intake valve is open then drop it and muffler into the pot and cover everything with antifreeze. Set the heat to 250F or so and let it cook for 30 minutes or so. It will come out looking like new. The heat will loosen and remove all of the baked on varnish.

When it’s done, let it cool and rinse with water. Put a prop on, rotate the engine to get the internal fluid out. Reassemble the engine and start it. It should run much better.
 
#3
A small amount of fuel coming out of the muffler is what you want. If you hold your hand in the exhaust for a few seconds, it should feel oily. If it’s slimly, that’s too much.

Every glow engine I owned would eventually get a coat of varnish. When varnished, the engine would only run fat (rich). When you leaned it out they would over heat and cut out.

The solution, boil it in antifreeze to clean it. Get the kind that is safe for aluminum, mix it 50/50 with water. Use an old crock pot or fondue pot. Remove the carburetor, muffler and glow plug. Rotate the engine so the intake valve is open then drop it and muffler into the pot and cover everything with antifreeze. Set the heat to 250F or so and let it cook for 30 minutes or so. It will come out looking like new. The heat will loosen and remove all of the baked on varnish.

When it’s done, let it cool and rinse with water. Put a prop on, rotate the engine to get the internal fluid out. Reassemble the engine and start it. It should run much better.
Perfect, I really appreciate the help.
 

Bricks

Well-known member
#5
You cannot adjust a glow engine or any engine for that matter at part throttle it has to be wide open to adjust the high speed and same goes for idle. High speed will always affect low speed once high speed is set then adjust low speed, and then visa versa. For cheap after run oil automatic transmission fluid will work great.

Before tearing it down how does the engine look if it does not look all caramelized and discolored I would hold off I have only had a few engines I have had to tear down and clean. Mostly tear down for bad bearings for me any ways.

Here is a good tutorial on how to set up your engine.

https://www.rcgroups.com/forums/showthread.php?205602-How-to-set-tune-your-engine
 
#6
You cannot adjust a glow engine or any engine for that matter at part throttle it has to be wide open to adjust the high speed and same goes for idle. High speed will always affect low speed once high speed is set then adjust low speed, and then visa versa. For cheap after run oil automatic transmission fluid will work great.

Before tearing it down how does the engine look if it does not look all caramelized and discolored I would hold off I have only had a few engines I have had to tear down and clean. Mostly tear down for bad bearings for me any ways.

Here is a good tutorial on how to set up your engine.

https://www.rcgroups.com/forums/showthread.php?205602-How-to-set-tune-your-engine
It's not particularly tarnished or discolored, I tried leaning it out more at full throttle and that definitely helped. It still isn't great, so I might tear it down. I appreciate the link!
 

Merv

Well-known member
#7
so I might tear it down.!
I agree with @Bricks, set the high side mix at full throttle. As you continue to lean the engine it will speed up, it will go faster, faster, faster, max out, then slow down. When you have leaned to the point it slows down, fatten (richen) it until you go back to max and it begins to slow again. If you have a tachometer, fatten the engine until it is 500 rpm below the max.

If you need to clean the engine, there is no need to take it completely apart, just the remote the carburetor, muffler and glow plug. Rotate the crank until the intake valve opens up, this will allow the antifreeze to easily get to the inside.