O.S. 25 FP glow engine, 10% nitro fuel, 6x3 prop. Started up my plane and was letting it warm up on the ground at about 1/3 throttle. All of a sudden, after about 2-2 1/2 minutes, it jumps up to full throttle. I moved the tx gimble to idle & checked the carb and it was closed down to idle where it should be. I then died. I tried to restart and it didn't want to start at all. I put fuel down the carb after checking the plug, (which was okay), carb at idle setting, and finally it started and again jumped to full throttle!

What is going on? It worked fine minutes before.


I put my finger over the carb and it still ran! It absolutely would not shut down from full throttle! I finally pulled the fuel line from the carb and after about 10 seconds it finally turned off.

I noticed a little smoke coming from the engine it was HOT! but it has cooled down now and still turns over fine.

I now notice there is fuel underneath the plane and upon taking hte wing off I notice there is fuel inside the plane. I think I developed a fuel leak from vibration maybe. I pulled both lines off the motor, pinched one and blew in the other. I could blow through it. Yep definately a fuel leak at the rubber part where the brass lines go through.

But could the fuel leak have caused the motor to stick in high rpm?

What should I do now? Fix the leak or install a new tank and fire up again? Or is there another problem I need to repair before starting again?

TIA for anyones help.

yes the fuel leak would cause the mixture to go lean which would greatly increase the engine speed, the engine can only take this a few times so watch it. If you can get just the rubber stopper then get a it but more than likely you'll have to get a new tank. It not worth trying to fix since any glue you use will take away from the elasticity of the stopper. This is how we build up our stock pile of spare parts.
now is this an .15 or a .25 a 6x3 prop would be really small. sm=confused.gif] a 6x3 would be too small for a .10

the 25 should have 8x6 9x5

Hi!

Why would the fuel go lean? Does it have something to do with the fuel pressure being different?

It's an O.S. .25 but the only prop I had was the 6x3 so I thought it would be okay to use to check the engine & radio glitches.

Thanks, I'll just replace the take.

I just don't understand the science......

G'day Mate, Sounds to me like the prop id way to small I run a 10x4 on an old OS 25 runs great. you said the motor kept running when you put your finger over the air intake, check the "O" ring on the carby, if it is leaking air the motor will go lean & it won't stop when you put your finger over intake. If your tank was leaking air, there would be less fuel pressure into the motor & so there would be more air, hence the lean run.
Godd Flyin Mate, Allan

Now I'm just taking a guess here but I suspect that with the 6x3 prop the engine finally decided that it was getting a bit warm at 30,000 revs or so. Next time you run it, could you PUHLEEEZE either beg, borrow or steal a tacho so we can find out how many revs it turns?

Hi!

I have a tacho. This engine on 10% with a 8x5 usually does 15,000 rpm. But I crashed the plane when an ail. servo stripped, just finished rebuilding her, and wanted to check to see if everything was Kosher. Guess not. I've got to pull the tank and check the O-Ring.

Thanks for the tips, I'll let you know how it goes.

R.

How did you even get a 6x3 prop on it? I would think there would be no prop hub left after reaming out the 1/16" or so hole! I bet it was at idle position and you just Thought it was at full throttle! That is a common prop for a Baby Bee not FP anything!

Actually it is a cut down 8x3.

Your problem is that you probably ruined your engine running that little toothpick on it. A 6x3 is and 049 prop and a TD 049n will turn one about 18,500 rpm. Even an 8x3 NOT cut down is way to little prop. A 25 likes 9x4 to 9x6. I would bet that you wore out the piston and cylinder and the lower end of the rod. Maybe even the wrist pin holes in the piston. That little prop would turn at least 25,000 rpm and probably more. That engine was never designed to do that.