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Cox Engine of The Month
Widow Fuel Mixing Question
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Widow Fuel Mixing Question
I have a Black Widow in new condition. I fly it three to four times a week on a plane.
It starts ok then when leaned for optimum rpm runs a bit sporadic for the first 30 seconds but maybe 90% ok. Then after 30 seconds into the flight it smooths out and runs pretty much perfect until fuel runs out. If I richen the mix more it runs perfect for the first 30 seconds then runs only 90% the rest of the run. So I suppose something to do with cylinder temperature. Is there a way to overcome this cold hot running matter? My other motors don't seem to suffer as badly as this widow.
Thanks
Ice
It starts ok then when leaned for optimum rpm runs a bit sporadic for the first 30 seconds but maybe 90% ok. Then after 30 seconds into the flight it smooths out and runs pretty much perfect until fuel runs out. If I richen the mix more it runs perfect for the first 30 seconds then runs only 90% the rest of the run. So I suppose something to do with cylinder temperature. Is there a way to overcome this cold hot running matter? My other motors don't seem to suffer as badly as this widow.
Thanks
Ice
Iceberg- Gold Member
- Posts : 382
Join date : 2018-11-03
Location : Suva Fiji Islands
Re: Widow Fuel Mixing Question
What fuel and mix are you using? New or old fuel?
NEW222- Top Poster
- Posts : 3896
Join date : 2011-08-13
Age : 46
Location : oakbank, mb
Re: 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?
Iceberg- Gold Member
- Posts : 382
Join date : 2018-11-03
Location : Suva Fiji Islands
Re: Widow Fuel Mixing Question
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.
Oldenginerod- Top Poster
- Posts : 4022
Join date : 2012-06-15
Age : 62
Location : Drouin, Victoria
Re: Widow Fuel Mixing Question
Oh and didn't mention the fuel is new.
Iceberg- Gold Member
- Posts : 382
Join date : 2018-11-03
Location : Suva Fiji Islands
Re: Widow Fuel Mixing Question
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
Ice
Iceberg- Gold Member
- Posts : 382
Join date : 2018-11-03
Location : Suva Fiji Islands
Re: Widow Fuel Mixing Question
Good recommendation on the venturi gasket. While you have it open, check the condition and placement of your fuel pickup tube.
Re: Widow Fuel Mixing Question
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.
Ken Cook- Top Poster
- Posts : 5653
Join date : 2012-03-27
Location : pennsylvania
Re: Widow Fuel Mixing Question
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
Here is a link to our troubleshooting chart: https://coxengines.ca/files/TSC.pdf
Re: Widow Fuel Mixing Question
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.
NEW222- Top Poster
- Posts : 3896
Join date : 2011-08-13
Age : 46
Location : oakbank, mb
Re: Widow Fuel Mixing Question
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!
Thanks!
Iceberg- Gold Member
- Posts : 382
Join date : 2018-11-03
Location : Suva Fiji Islands
Re: Widow Fuel Mixing Question
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.
Re: Widow Fuel Mixing Question
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.
Note: Use only silicone grease on Cox engines in general. Ordinary grease is incompatible with delrin according to compatibility tests.
Levent Suberk- Diamond Member
- Posts : 2271
Join date : 2017-12-24
Location : Türkiye
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