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Author Topic: Cox 049 poor run  (Read 1087 times)

Offline Pepper Kay

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Cox 049 poor run
« on: October 02, 2006, 08:12:38 AM »
Hi All:

Just mounted an  old 049 to a QTee for some fun flying and get a very poor engine run ...

Engine runs great on the stest stand ...

I note on the backplate, there is a small hole covered with a very fine mesh screen ... is that a breather of some sort ? ...

Were I to drill a hole in the firewall directly behind this hole in the backplate, would that improve the running ?? ...

Thanks,

Pepper
AMA # 3937
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Pepper Kay
Garland, TX
AMA # 3937

Offline Tom Perry

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Re: Cox 049 poor run
« Reply #1 on: October 02, 2006, 08:29:10 AM »
Pepper,

There should be planty of air reaching the intake if the engine is mounted properly.  Make sure the area that is recessed in the back plate is not block to insure good air flow.  To answer you origional question drilling the hole won't hurt but should not be necessary.

 #^
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Tight lines,

Tom Perry
 Norfolk, Virginia

Offline Pepper Kay

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Re: Cox 049 poor run
« Reply #2 on: October 02, 2006, 08:39:14 AM »
Hi again:

One thing I forgot to mention is that I mounted the Cox directly onto a lite-ply former - it is solid ... the engine is not mounted on a Cox, Tatone or other engine mount ...

With that hole in the engine's backplate covered, I believe it to be causing the poor engine run, as it runs fine in the open air on the test stand ...

Thanks,

Pepper
AMA #3937
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Pepper Kay
Garland, TX
AMA # 3937

Offline Ralph Wenzel (d)

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Re: Cox 049 poor run
« Reply #3 on: October 02, 2006, 09:57:32 AM »
Quote from: Pepper Kay on October 02, 2006, 08:12:38 AM
Hi All:

Just mounted an  old 049 to a QTee for some fun flying and get a very poor engine run ...

Engine runs great on the stest stand ...

I note on the backplate, there is a small hole covered with a very fine mesh screen ... is that a breather of some sort ? ...

Were I to drill a hole in the firewall directly behind this hole in the backplate, would that improve the running ?? ...

Thanks,

Pepper
AMA # 3937

That "hole" is the engine's air intake; like the venturi on a "normal" engine. It's amazing that it runs at all with that blocked off!
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Ralph Wenzel
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Alan Hahn

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Re: Cox 049 poor run
« Reply #4 on: October 02, 2006, 11:50:31 AM »
Pepper,
All of the Cox backplates that I have looked at have a relief cut into the backplate which will admit air into the venturi opening (which has the mesh cover to keep out pieces of grass and dirt). This even works when you mount the engine flush with a solid piece of wood.

I would venture that your poor running problems are probably coming from the reed--it may be sticking or not sealing to the tank, and cleaning this may be the best bet. However I warn you to take things apart over a white piece of paper so that you don't lose parts--especially the tiny rubber gasket that fits between the internal stack of the venturi and the inside of the backplate--next to the spraybar area. This is very tiny and can easily be lost. If it is left out, you will also experience poor running due to air leaks (and fuel, depending on how low the fuel level is) directly  into the downstream side of the venturi. It is easy to replace a lost gasket with a very fine slice of 1/2 A fuel tubing, but the best is not to lose the gasket in the first place!
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Offline Clancy Arnold

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Re: Cox 049 poor run
« Reply #5 on: October 04, 2006, 01:56:16 PM »
Pepper
Having owned about 20 COX 049's and have 2 in planes now, I think I may be of some help.  Most of the comments here refer to the engine that has a built in metal tank.  There are also engines with a plastic backplate that require a separate fuel tank.  The comment about the hole in the backplate with a screen over it is correct, that is the intake.  The problem of air starvation in the plane has been attacked by COX two ways.  The type with a metal fuel tank built in has a grove molded into the metal backplate for air.  The one with the plastic backplate were later equipped with a venturi extension that bolted to the engine and extended the venturi up the rear of the engine.   This requires a slot be provided in the firewall to clear the extension.    My fix for this problem on the plastic backplate is to remove the screen and cut away the plastic that the screen was mounted in back to the point that the venturi wall gets thicker.  This gives me about 1/16 inch space between the venturi and the firewall when I mount the engine.  I have been doing this to COX engines for about 20 years with no problems. 

there are at least 3 or 4 different reed valves I have seen and they are NOT interchangeable.  Even the reed valve retainers are different and different size!

Hope this helps.
Clancy
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Clancy Arnold
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Offline Pepper Kay

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Re: Cox 049 poor run
« Reply #6 on: October 04, 2006, 04:21:03 PM »
Hi All:

Thanks to one and all and the good advice, I did what was suggested and the problem is solved ...

The engine now runs fine, both on the airplane and on the bench ...

Again, many thanks to everyone ...

Pepper
AMA #3937
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Pepper Kay
Garland, TX
AMA # 3937

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