Cox Engines Forum
You are not logged in! Please login or register.

Logged in members see NO ADVERTISEMENTS!

TD/Medallion .049 fuel draw issues Cox_ba12

Log in

I forgot my password


Display results as :

Rechercher Advanced Search

Latest topics
» Camping for the weekend
by akjgardner Today at 12:13 am

» music vids.. some of your favorites
by Levent Suberk Today at 12:05 am

» Guillows Piper Chrokee Rubber Powered
by rdw777 Yesterday at 11:00 pm

» The third Cox Beaver chainsaw.......with a surprise
by rsv1cox Yesterday at 10:38 pm

» The New CEF App
by getback Yesterday at 10:20 pm

» Bell P-39 Airacobra and P-63 Kingcobra confusion but so interesting
by rsv1cox Yesterday at 9:16 pm

» Brodak Baby Ringmaster
by Ken Cook Yesterday at 6:22 pm

» USPS rings the bell and Cox goes to war
by rsv1cox Yesterday at 2:36 pm

» .010 TeeDee Tiny Speeder
by 1/2A Nut Yesterday at 8:30 am

» Norvel engines and parts.
by Ken Cook Fri Sep 22, 2023 10:14 pm

» My "fork" stooge for tricycle-geared 1/2A R.O.G. launching
by roddie Fri Sep 22, 2023 9:57 pm

» cheap jet attempt 2 "the revenge of the runner"
by Oldenginerod Fri Sep 22, 2023 9:30 am

Cox Engine of The Month

"Beefed up old stock 290 on my Quickie100 RC after plenty of airtime hours..."

CEF Traveling Engine

Win This Engine!

TD/Medallion .049 fuel draw issues Empty
Live on Patrol

TD/Medallion .049 fuel draw issues

Go down

TD/Medallion .049 fuel draw issues Empty TD/Medallion .049 fuel draw issues

Post  Droobie Wed Aug 30, 2023 5:02 pm

Hi all. I Have a TD and Medallion .049, and my father a TD .051. His was new out of the box, and both of mind have been reconditioned with new top ends. They will run fine on the bench, but I can not get either of mine to start or run consistently on the plane, and I am including the .051 my dad has in this as he has had the same issues.

Most recently, I have my medallion mounted on a fresh baby ringmaster rebuild, with a brand new Perfect tank. I have the tank immediately behind the motor, and the fuel pickup is a close to dead-nuts on center of the motor as you can get without being a machinist, haha. I also have the needle valve assembly flipped so when the motor is mounted on its side with the cylinder outboard (talking CL here), the needle is up and the fuel pickup is down- again, same as I would on any larger motors I set up without issue.

Running it last night, first- it takes what I consider to be an obscene amount of priming/choking to get the motor to even try to start beyond just a single "pop" every flip. Once its so loaded with fuel that it bumps on every flip, after 5-6 flips it will fire off and then quickly die, as if it is lean. I was playing very close attention to the fuel line and seeing bubbles, so I started leaning the plane a bit and finally was able to get it to start and stay running, sorta/kinda. I learned recently that closing off one of the two vertical tank vents will help motors draw fuel, I tried that with no improvement/change. There was a mixture of tiny bubbles, likely from vibration- I don't have foam under the tank and know I need to address that, but the lager bubbles were definitely confusing. Even with the plane tilted to "simulate" the centrifugal force and keeping the pickup tube completely submerged, the engine speed would still wander as moved the plane and bubbles would appear, eventually killing the motor prematurely.

I know most of this sounds like issues with my tank. I am running Brodak 35% castor fuel which all my other Cox engines absolutely love, and again- these motors run fine on the bench. The TD is mounted on a scratch built plane with the tank inside the wing, essentially on the centerline (of the wing) but definitely below the centerline of the engine with a longer fuel line. Interestingly, this one runs/starts a bit better- which is kind of baffling to me?

I guess my primary questions are

(a) do these motors need the tank mounted differently (i.e. not on-center)? I have two remote-tank "bee" engines that also have similar issues with fuel draw, however they do start and run fine on the ground- just suffer once in the air.
(b) does anyone get good performance with regular suction tanks or is a bladder tank the only answer?
(c) do they just hate being mounted sideways?
(d) should I try flipping the NVAs over so the fuel draws in from the top? Is that a known issue?

We desperately want these motors to run great! Its so aggravating having them, building models around them, running them on the bench and then kneeling in the sun at the flying field for 10 mins to get them to start, only to launch and get a lap or two before they die. Just hoping some TD/Medallion gurus here can weigh in with some good experience and tips, many thanks!
New Member
New Member

Posts : 3
Join date : 2023-07-24

Back to top Go down

TD/Medallion .049 fuel draw issues Empty Re: TD/Medallion .049 fuel draw issues

Post  aspeed Wed Aug 30, 2023 7:21 pm

Could be the plane's motor mount is somewhat weak and is shaking making the bubbles. I have had that happen. Maybe a cheek cowl will strengthen things up if it is the profile type. Prop imbalance could make it worse. Suction should work if the carb hole has not been drilled out. Check normal things like holes in the tank or lines. I cover all the tubing holes with my fingers and suck on the easiest one and plug it with my tongue to check. Should seal for over a minute. No fuel in the tank of course.
Platinum Member
Platinum Member

Posts : 775
Join date : 2013-01-19
Location : Leamington Ont. Can.

Back to top Go down

TD/Medallion .049 fuel draw issues Empty Re: TD/Medallion .049 fuel draw issues

Post  balogh Wed Aug 30, 2023 7:32 pm

Droobie, I can chime in only with my RC experience as I only fly RC. My 049 TeeDees never suffer from fuel starvation or foaming/bubbles in the fuel line, thanks to the unpressurized balloon tanks I use. These are made of party balloons and have only a filling and a fuel line through a stopper in the balloon neck I place the balloon tank in the front compartment to be roughly level with the engine carb, and as near to the firewall as possible.
Though it is indifferent whether the engine runs on a bench or in a plane, unwanted air ingress into the carb along the NV thread may cause symptoms that you described. Just to be on the safe side, you may want to pull a piece of silicon fuel line on the threaded end of the NV such that it also overhangs the threaded end of the carb, to prevent air seeping in along the threads..

Looking forward to hearing of the solution you find efficient at the end..
Top Poster
Top Poster

2022 Supporter

2023 Supporter

Posts : 4551
Join date : 2011-11-06
Age : 64
Location : Budapest Hungary

Back to top Go down

TD/Medallion .049 fuel draw issues Empty Re: TD/Medallion .049 fuel draw issues

Post  Sponsored content

Sponsored content

Back to top Go down

Back to top

- Similar topics

Permissions in this forum:
You cannot reply to topics in this forum