Building Tips and technical articles. > 1/2 A building.
Questions about Cox tank backs
ken cook:
Recently, I had about 4 or more of my tank backs for my black widows crack. Larry feel free to chime in here. I recently purchased 4 tank backs and 1 conversion 8cc kit. And you think gas is expensive. My older tank backs have no filler vent pipes, the new ones have one and a small vent hole. The 8cc tank has no stunt pipes, my old ones do. This tells me that there might be consequences with long time inverted flying with no stunt tank. Is this the correct assumption? Prior to purchasing the newer tank backs, I pulled some older die cast baby bee tank backs out of storage. I installed these on the black widows and plugged the two filler pipes on the tank back. The engines ran but not quite the same. I found during starting the cylinder was spitting fuel out all over as if it was too rich. My theory is that the baby bee tank back has too small of a intake hole. I haven't taken the engine off to check it yet. I then installed the new tank backs on the older black widows. I now have the old stunt tank with the new tank back. What is going to happen with this set up? Is fuel going to pour out if I go inverted? Its a bit difficult to cap the new arrangement on the new tank back unless you epoxy the holes closed. I really don't want to do this with these newly purchased jewels. Do you think it would be wise to just change the tanks to the newer style ? I have some real good runners here and just seeing them in a box is a real heartbreaker. Thanks, Ken Cook
George:
Toward the last, Cox used the Texaco setup with the fill and vent on the backplate and the tank unvented. They also switched from an aluminum tank to a plastic one, I believe. At one time I could not tell the difference (online site add pictures) between the Babe Bee, the Black Widow, and the Texaco. All appeared to use the unvented tank setup and the Sure Start front end.
Again, this was from looking on the Cox site...perhaps the pictures were not correct.
George
Paul Smith:
I'd say, just epoxy shut the holes in the Babe Bee backplate.
These engines are really picky-picky about tiny leaks, better safe than sorry.
You can just drill 'em out if you want to change back.
ps:
Not all venturis are created equal. Mike or gauge the air intake to get what you need. You can't always get what you want.
Larry Renger:
I agree about epoxying up the holes. Those backs are Nylon, and the epoxy will be easy to remove if you ever need to.
Also, beware, some C*x engines made in the late '80s (before I went back and fixed the problem!) had larger openings in the backplate than the venturi. Bad, bad news for good fuel draw. The venturi should be the same size or larger than the hole in the backplate.
Also on old backplates, check the screen, if it still has one. They can be really blocked up with old, congealed castor oil. I just remove the screen and smooth the inlet to remove the screen retention ridge.
Clancy Arnold:
Larry
You are a man after my own heart! I have been removing the screen and trimming the venturi end off of the plastic "U" backs for 2 years. It gives more space between the firewall and the venturi allowing better air feed. I trim the plastic back to the ledge that the screen was against. Have never had a problem since. Now I will start doing the same to my metal tank backs also.
Do you know of a source of plastic backplate/motor mounts for Cox 020 Pee Wee's?
I hate the idea of drilling a hole in the side of the metal tank to run a separate fuel tank.
Clancy
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