I own a .049 Cox engine and it ran really good for a while and now it wont even act like its trying to run. And today iv been messing with it for a good 5 hours, and i noticed that the whole time the cylinder was dry of fuel (exept a couple drops here and there) no matter how much i primed it. So just as a experiment i took the glow plug off and put a drop of fuel directly in the cylinder and then tried to start it. It ran perfectly for about a second or two (untill the fuel in the cylinder was burned up) then it immediatly died as if out of fuel, but it has 3/4 of a tank in it. So i think there is a problem with the engine pulling fuel into it. I cant figure out what to do, and i tried calling Cox and theres no answer there. Can someone here help me?

Fox

P.s. ill be glad to explain more as to whats happening if needed.

you have done a good job of diagnosing so far. clearly there is some blockage of the fuel between the tank and the combubstion chamber. First place to look is the needle valve. Unscrew the needle valve completely and try to see if there is some dirt or something blocking the passage of fuel thru the NV assembly. Sometimes a very small diameter wire can be used to clean out the fuel passage. This engine relies on a reed valve to allow fuel to suck in to the crankcase. the reed may be malfunctioning. thr reed is a very thin metal between the integral tank and the crankcase.

You should be able to get it to run in a brief burst after priming through the exhaust ports.

It sounds as if either the fuel-pickup tube has fallen off the nipple on the back of the tank or the very fine hole that feeds the venturi is blocked.

I assume this is a Baby-bee-type engine with the built in aluminum tank?

If so, remove the tank and check that you can blow air through the fuel-pickup pipe and that it comes out the venturi

Also check the needle-valve to make sure that the very tip hasn't broken off and lodged in the fuel jet.

Other than that, I suggest you ask your question over in the 1/2A forum where there's a wealth of experienc with these little engines and everyone is very friendly.

Could have a stuck reed (a bit of dirt behind it so it wont close and seal) which is very common.

Take the 4 screws off the tank from the rear end, pull off the tank and you will see a C clip holding on a reed (or on the newer engines a black plastic retainer). Remove carefully and donot distort the reed. Clean and reinstall.

Like Xjet suggests, the pickup tube inside the tank may also be blocked, a bit of dirty fuel and it is easy to do.

The main thing is these engines like CLEAN fuel...

Good luck and if you are in any further trouble, try us out in the 1/2A forum here, its where the most help wil come from

AJC

XJet:

Actually the engine and fuel tank are connected by a tube.

Everyone:

I believe i fixed it, i compleatly unscrewed the needly valve (not compleatly off but far enough to where it wasent in the fuel line at all) and then i tried to start it. Soon enough gas spurted out of the from of the engine (the air intake) and then she started right up. Runs really rough tho and only for 5 seconds or so befor she spudders out and dies. Im not sure exactly whats wrong but im getting closer to finding out. The reed valve thing was bent a little bit, i fix it with some pliers and now it works better. Thanks for the quick help!

Fox

P.s. Is gas spose to spit out of the engine while its running? after each flight i have loads of gasoline on the wings and tail of my airplane, and while im tweaking it befor the flight it spits alot of gas onto my hand. (about the same as if you made that engine noise [when you put your tounge partly out of your mouth and blow] with your tounge a couple inches from your arm...thats about how bad it spits.) Is that normal?

it is normal for glow engines to exhaust some unburnt fuel and of course all the oil. the fuel is approximately 80% burnable stuff (alcohol and nitromethane) and 20% oil. the oil does not burn. it just flows thru the engine to provide lubrication and cooling.
But it sounds like you are running the engine too rich (needle valve opened too far). You need to find the sweet spot in the needle valve where the engine runs best. too lean (clockwise) and the engine will not get enough fuel to run. too rich (counterclockwise) and the engine gets too much fuel. Your symptoms sound too rich.
But even at the perfect setting, there will be alot of residue on your plane - mostly oil.

Hi!
It is also vital that you run these small COX engines on good fuel! Use at least 10% nitro....preferable 20%-25% and a good prop like a 6x3 or 5x3 ...7x4 is too large if it is a COX Babe-Bee or Black-widow.
Also see to that you use the high compression head on these engines ..originally made for the TEE-DEE 0.049 and 0.051 series of engines.

Regards!
Jan K
Sweden

Fox:

What Jaka didn't tell you is that Cox engines don't live very long if run without castor oil. 22% oil is best, but Omega 25% will work. Adding 4 ounces of castor to a gallon of Omega makes an excellent fuel for the Cox engines.

Bill.

Hi!
Well ...I run my COX engines on 15% all synthetic oil (Motul "Micro")...

Regards!
Jan K
Sweden

Jan,
There are actually a lot of fellows in SAM that run 15%, 100% synth oil, in the cox engines - me being one of them. As long as you are running a larger prop (7 or 8" diam) that keeps the rpm's down, they do run really well (I have many hours on certain engines with absolutely no adverse effects). However, if you are running a smallish prop for high rpm, or tend to set your engines on the lean side, I suggest you go with a bit of castor, if nothing more than for the ball/socket joint. Just my opinion...

AJC

There is a current thread on the 1/2A forum about 1/2a fuels. Consensus is that for the ball/socket joint on Cox and the big end bearing on Norvell castor is a must. It seems quite logical though as ajcoholic points out, for low rpm use (1/2a Texaco, etc., synthetic should prove adequate, and I would think reduce varnishing. I also expect that using lower nitro % should give better "mileage". Kick the RPM up though and castor is cheap, reliable insurance.

jess.

That right Jess - you cant expect to run them screaming in the high teens though, and last without some castor. Thats been proven also

AJC

Hmmm - all synthetic and you lose the ball socket. All castor and you have a varnishing problem (how many used Hopps gun cleaner, a metal brush, or both to remove varnish?). How about a combo of both lubes?
I am surprised that the Texaco doesn't get excessive wear with low oil content considering the larger load on the conrod with the large prop...but you can't argue with success.

George

Hoppes works well, though I think the older, more toxic Hoppes was better. I have heard that automotive fuel injector cleaner works.

In any event I find the reed valve Coxes enough aggraivation that I generally avoid them. I don't compete, so I conserve my more colorful language for other things.

jess.