Widow Fuel Mixing Question

I am using a 30% nitro with about 27% oil mostly synthetic and 5% castor I know a bit much oil but it runs great in my other motors?

Maybe the venturi seal??  If you set it rich with a full tank, then after a while the fuel level drops below the venturi tube and it leans out, hence the smoother running.  If you set it lean with a full tank, then it goes over-lean when the fuel drops below the tube and starts to suck air.

Oh and didn't mention the fuel is new.

Great suggestion yes the widow is new. I have flown maybe 15-20 flights only. Never opened it hoping for a 30 year museum piece. Yes likely the Venturi ring is deteriorated. Will check it. Many thanks!

Ice

Good recommendation on the venturi gasket. While you have it open, check the condition and placement of your fuel pickup tube.

A Black Widow is going to want to run optimally therefore everything has to be spot on for it to work properly. Prop size is important, it wants a 5x3, yes it can work with a 6x3 but it's not going to be happy like it will be using a 5" prop.  Checking these engines for air leaks are a must. You can't check them unless you have a suitable syringe and a small one isn't going to work. You need a large syringe. Place oil on the needle where it enters the backplate, oil every screw hole, put oil on the joint from case to tank and backplate to tank and begin to pressurize the filler pipe watching for bubbles where the oil has been placed. At no given time should you be able to fully compress the syringe otherwise your leaking. Lend your ear to the screen on the backplate and this will confirm if your venturi o-ring is leaking without the need to take it apart. You will more than likely discover one or more of the leaks I have suggested. You can't diagnose further until all of them are remedied.

With a castor oil content of only 5% you run the very real risk of damaging the engine.

Here is a link to our troubleshooting chart: https://coxengines.ca/files/TSC.pdf

Sorry I'm late coming back to the party, but I do think you can eliminate the fuel as a problem. I too would agree that there is a leak somewheres in the system. I reall do like Kens way of doing it by the sounds of it to get a quick full diagnosis, and also sounds very thurough. But I myself personally would start with the venturi 'o-ring' as others have mentioned, then check everywhere else. To me, it is that the o-ring is a quick and easy part to swap out.

Got the Venturi gasket changed last night. Fuel pickup line was good and clean no cracks or other. If Ken would've written earlier would have done that before the tear down. Will still do that though. Will get the bird up in the air in a day or two and will report back. Double checked my fuel is 6% Castor plus 23% synthetic. Discussed at length a couple months back. Fuel is good.

Thanks!

Iceberg wrote:Got the Venturi gasket changed last night. Fuel pickup line was good and clean no cracks or other. If Ken would've written earlier would have done that before the tear down. Will still do that though. Will get the bird up in the air in a day or two and will report back. Double checked my fuel is 6% Castor plus 23% synthetic. Discussed at length a couple months back. Fuel is good.

Thanks!

We do sell the pistons when the conrod ball has worked it's way through the top of the socket due to lack of castor oil https://coxengines.ca/cox-.049-piston.html

There was a study made years ago made where the tester's consensus was that such a small percentage of castor oil most likely will lead to piston failure but then, your oil content in general is quite high, so you might get away with this.

If it is not from venturi gasket, remove glowhead and smear a little high temp grease on glowhead threads.

Note: Use only silicone grease on Cox engines in general. Ordinary grease is incompatible with delrin according to compatibility tests.