EngineJunkie

I have a cox .49 engine with standard fuel tank. I just replaced the fuel line (inside the tiny fuel tank). Although the engine starts first try, as the fuel in the tank is burned the needle valve needs frequent adjustment (about 3 times per tank) to maintain full power. Any thoughts on this would be helpful. Thanks!

flyinrog

My Feedback: (1)

you need to head over to the 1/2a (.049) forum,,the engine like most others should be peaked and then backed off a notch or 2, sounds like there is an air leak somewhere or perhaps the glow head is going south or if it sat for 20 years like they often do it needs a thorough cleaning... they need high nitro %25-35 and %20castor for lube,,it might run on %10 cool power but, not well if thats what your trying.......Rog

B.L.E.

You are talking about the Cox .049 reed valve engine I assume. The fuel tank is the back plate for the crank case. An air leak between the fuel tank and crank case will have you chasing the needle valve all over the place. Try a little silicone rubber on the gasket between the tank and crank case.

Remby

My Feedback: (3)

Check for varnish buildup in the cylinder, remove it if there is some buildup. Glow head is suspect as stated before here. A blockage in the passages is also somthing to check for. Air leaking past the seals, check and fix. Should go good then.

lukesp

I agree with Remby re the varnish build up and possible air leaks. Varnishing is a hassle if you're unaware it. How old is the engine, do you know ?

j.duncker

My Feedback: (2)

The key is the fact you replaced the likkle fuel tube inside the tank.

Bet you have a leak in the tube possibly at the spigot.

Are you sure the tube is not to long this will cause buckling at the spigot.

ptulmer

My Feedback: (5)

Well, he said he had to readjust it about 3 times. It doesn't really sound like an airleak type problem. It sounds like a needle that's turning due to vibration. Was the spring reinstalled? Has the spring been sprung? I guess what I'm asking is whether the needle is actually turning itself out of adjustment?

Remby

My Feedback: (3)

True, the needle can turn through vibration, and as he is bench running, just look at the needle as it runs to see. If it is self turning, check the prop for running true, it can cause this to happen. Also, bent prop screw if bad enough.

Andrew

Does your engine have the brass backplate or plastic? The plastic backplates can deform if the screws are too tight -- try to keep them evenly tightened and snug, but not torqued to the max. Another area that can be a problem, especially after disassembly, is the venturi gasket. If old or compressed, it may not be sealing well and sucking fuel with a full tank or air after the fuel level drops. I've found the venturi seal to cause the most aggrevation of all the gaskets in the reedies.

If your needle is backing out, then the adjustments will be in the same direction each time, ie. you would need to continue to lean the mixture.

balongski

i have this cox engine lying around for some time now, i remember when i burnt the glow plug cylinder head assy with 12 volts car battery( I hooked it up not knowing how to fire it up I was so stupid ) 10 years ago untill i met my friend who's into rc, he told me how to fire a nitro engine, the engine has no tanks in the back like what i see on the web, it has a needle valve and a nipple located at the back plate ithink it uses an external or seperated tank the thing is can any body help me how to do the plumbing and the correct level of fuel tank how far it should be. it fires on morgan 15% heli fuel and i change the plug into number 8 OS i tapped the glow plug. because there are no parts available here in the philippines

MJD

My Feedback: (1)

The fuel tank centerline should be level with the intake on the rear of the engine or just a tiny bit below that. The fuel draw is not strong, so the fuel tank should be as close as possible to the engine, otherwise your mixture settings will be erratic. A one ounce fuel tank is lots, in fact more than you need most of the time. Normally a retapped glow head like yours will not perform as well as the Cox glowhead, but will still run, and at least you can get replacement glow plugs.

gcb

It could be, as someone mentioned, that the needle is turning due to vibration. Needles are also noted for leaking. Remove the spring and seal the needle using fuel tubing. This will prevent leaks and adjustment changes due to vibration.

Next...inside the tank, there is an "O" ring seal between the backplate and the tank. This can be lost or pinched. Your symptoms would indicate some leakage so that the leak becomes part of the fuel adjustment. If so, when the fuel drops below the center it sucks air, resulting in a leaner setting for which you would need to RICHEN the setting (you didn't say how you had to adjust).

Of course it may be a combination of this and vibration. Make sure your prop is balanced and running true.

Hope some of this helps. Good luck.

George