I would use a larger tubing simply just to get more fuel to the engine. As for the engine using a smaller prop and over heating, I say no. The reason is this, letting the engine unload using a smaller prop would reduce the load on the engine and not produce as much heat because you are blowing more air across the cylinder head at a slight higher RPM. You have to realize that the props recommended for this engine is based on what the engine is used in. For instance, the 14X6 might be used in a Piper Cub with an 80" wingspan where the 12X6 might be used in a Edge 540 with a 60" wingspan. Two complete different type of flying. let me know what you find out....

Larry/Instructor

Larger tubing is not the answer. I run a YS 115 that at full throttle drinks 4 oz per minute. I run 1/8" tubing. Imagine drinking through a normal drinking straw, then a garden hose. The larger garden hose has the potential to provide more fluid but requires much more force to move it. A 13x6 is pretty much the ideal overall prop for this engine. The setup has worked well in the past........what changed? The lack on a fuel filter is a huge clue. Once again, remove the needle valve assembly. I beleive the engine even came with the 7mm or 8mm wrench required to do this. I'm 90% sure you will find some debris. The inconsistant running comes from the debris moving around some.

Increasing the diameter of the fuel tubing will make no difference. The fuel nipple on the carb can only take in so much fuel due to its size and is further limited by the ls and hs needles. Installing 5/32" id line will not give the engine more fuel . .....all it will do is fall off of the fuel nipple.
If you can somehow install a 120 carb on it then the larger line will fit and deliver more fuel.....but it won't run !!
Also a 13x6 prop is fine on a 60 size engine. Used to run one on a 60 glow and now I run a 13x6 on a 10cc gasser and your 65 glow makes more power.
You are getting advice that is all over the map....like people throwing darts hoping one gets close !
My advice stands to check for air leaks in the carb, line, tank, engine, etc... As some suggested, install a piece of tubing over the hs needle and see if the problem returns. Not the first time a new carb had problems.

I had one engine that would vibrate the
needle closed. It never overheated, but
would just quit when it got too lean, but
it was the nature of that engine to quit lean.

Have you noticed the position of the needle
when it overheats?

Jenny

I still got my money on the fuel line. You can be as rich as you want, but losing pressure in the tank will do it all of the time.

Hi Champ,

I was wondering about you being the original owner because I wanted to know if the engine was old with perhaps lots of unknown time on it and therefore lots of wear and even castor varnish build up inside. I couldn't tell from the pictures. Your answer above rules that out.

So I'm in the camp of there is something causing it to lean out. Lean = heat. A pinhole in one of the fuel lines or some obstruction in the carb sounds right. Replace all the lines and tear down/clean the carb. Good luck.

Lars

you have a air leak replace the fuel lines all of them and check the stopper on the tank they can leak and you not know it therefore the engine will lean out , you can get a pin hole and it will drive you crazy or seal leaking on the carb its is one of them

Good point Jenny, I haven't thought of that. I do have an extension on that needle too. I'll take notice on my next flight.

Try a different jug of fuel. I have had some fuel that would make my engines run hot no matter how I tuned them. Borrow a tank of fuel from a buddy and see if it helps any.

I would run a 11/8 or 12/6 on a 65 FS engine
13/8 or 14/6 on a 91 engine
I bet if you unload it some you'll notice it will be easy to tune and run cooler
I also run 30% heli fuel in all my engines for extra lube

Does the crankshaft move freely in between compression strokes..?
A well fit engine should "toggle" back and forth when you test flip it.
A "runaway" heat condition can originate in the bottom end.

Maybe condensation(water in the fuel) sometimes happens if rcers' use a tin gallon container or maybe to much nitro content?? Easy to test these-borrow a tank of fuel from a fellow modeler that is using a different brand of fuel that is pumped out of a plastic gallon container, GOOD LUCK.

That's a good point about the fuel. I just remembered I broke the engine in on Torco 10% Nitro fuel. After I finished that gallon I switched to Cool Power 15 % nitro. Does running a fuel with different nitro content than what I broke the engine in with make any difference? I just can't say fore sure that this problem started when I switched to the 15% nitro. The specs for the engine allow for a nitro content of 5-10%.

Since you mentioned that the tank
was a "very snug fit" there is a good
possibility that the fuselage vibration
is causing the fuel to foam. Running
a prolonged time at the speed where
the vibration resonates would make
the engine overheat. It wouldn't need
to be at full throttle to go lean with
foaming.

The solution is a smaller or differently
shaped tank with more foam around it.
Also a different propeller could help.
A couple of drops of fabric softener in
the fuel could reduce its tendency to foam.

Jenny

Champ,

The amount of nitro content fuel you are talking about will not make a difference. You should retune after such a switch and it sounds like you have. I read that some are suggesting higher nitro and also heli fuel. While that wouldn't hurt and the engine will run fine, that is not necessary. Your engine and the plane/setup you have it in is very standard and certainly not exotic. 5%/10%15 nitro is just fine. As I said before, something is causing it to lean out.

I must have missed the tight fitting fuel tank information, so foaming as Jenny mentions could also be a culprit. In that case, I would expect you would also get some surging as you are flying. Is that happening?

Lars

And run a wire or something through the pressure tap fitting on the muffler to make sure its not clogged up.

It could be varnished up, although it looks pretty clean on the outside.

Boy you guys know how to blow thing out of portion. Comparing a drinking straw to a garden hose is like comparing 1/8" fuel tubing to 3/8" tubing. I simply said I would use larger tubing. Anything above .50, I always use larger tubing. A glow engine is no different than a car engine. To get more power, you need more fuel. Did I ever have trouble with the fuel tubing coming off the fuel nipple, sure, but I corrected that problem using Du-Bro fuel clips or using a small piece of fuel tubing cut to 3/16" length and installed over the fuel tubing going to the fuel nipple. Also, using a 20cc gas engine to turn a 13X6 prop is not the same as a glow engine. Most gas engine produce more torque, so they can turn a larger prop. Have I ever seen a .61 turn a 13X6 prop, sure I have, but it was a APC prop.

All the advise we have given the OP is based on our experience. We don't know his flying style, and also he is at sea level. Someone said check the pressure tap on the muffler and I agree. Also make sure the opening is at least 3/32". I'm sure he will find the problem and I hope he does.....

Larry/Instructor

Your right on however he mentions nothing about bubbles in the draw line. I would completely go through the fuel system starting with the tank.

Hello,

I'll just throw in my 2 cents worth & hopefully it will help you in some way. I have been in the hobby since 1989 & have had 2 engine failures early on in my R/C career. Both failures were due to excessive prop pitch which caused excessive overheating. Heavy engine load causes overheating. Since the 12 x 6 prop is on your engine manufacturer's recommended list & you have already checked every other thing our fellow R/C pilots have posted here, just install one the next time you go out to fly. Check the results & let us know what the outcome was.

Cheers & Happy Flights!

Jay Dub

The APC 13x6 is a really narrow bladed prop, I have run a couple .61 FX engines with them and they have worked very well. The .65 should have no issues with it. I don't think the OP has tried everything suggested. My suggestion to pull the needle valve assembly from the carb to look for debris has yet to be done. I have experienced the exact same symptoms a few times and was only able to clear the fuel passage after removing the needle assembly. The part I'm referring to is # 7-4 in the exploded veiw.

Thanks for the diagram speed.

I'm working on the plane now. I did notice that I don't have any foam around the fuel tank. When I try to place 1/4" foam under it the top of the tank presses against the fuselage beam that arcs over the tank and the neck of the tank no loger lies up with the opening in the firewall so the tubing needs to route down and through the opening. The manual doesn't say anything about using foam and the pictures of it shows that the tank installation does not have foam. Should I still try using foam under the tank? I always thought this was a standard requirement for nitro gas powered aircraft.

Yep it sure does.

Champ,

isolating the the tank with foam couldn't hurt. You might have to make some small modifications to do so. I also agree with Speedracertrixie if you haven't done that. Tell us, as you are the original owner of the engine, did it ever run fine without the problem? Can you elaborate on that a bit?

Lars

As Lars states it does not hurt to run foam however it is not the end of the world if you don't. These days our fuels are blended with anti foaming additives, you would have to have a serious vibration issue to have this be any real consideration. Years ago when I flew helicopters we actually bolted the fuel tanks to the helicopter frames. None of my current fleet have foam. I simply use sticky backed Velcro to secure the tank from moving and then a couple Velcro straps to keep it in place. I religiously do use quality filters though.