How to cool down a pressure fitting
 

Hello:

I have a simple question i have the evolution 10cc gas engine mount on my meridian 10cc plane, i had to discard the stock muffler (it's awful) i purchased the scotsman muffler from macs muffler and it's a great muffler, but i am still burning the stock viton fuel lines coming from the pressure fitting i think this engine it's too hot to handle those temperatures, i am running a 12x6 APC prop running at 10,500 RPM on the ground i am thinking to place a brass coil to extend the lenght of the pressure fitting to see what happens i will appreciate any ideas or comments you might have.

A line hooked to a muffler on a gas engine, whether it be for a smoke system or for tank pressure needs to be made of rubber. The rubber will withstand the heat. The various standard lines/hoses for gasoline use won't take the heat, as you have found out. The way the fuel line to the carb on that engine runs almost if not actually touching the cooling fins on the cylinder, you probably should use rubber tubing for the fuel line too. The advertising mentions that they supply special high temp tubing, (probably just rubber) for use with the engine, so this is a known problem.

If the fitting is large enough on the muffler, you could drill it out and extend it by inserting some 1/8" brass or copper tubing. But the extension will need to be brazed with bronze or silver braze, once again to tolerate the heat. Even the so called silver solder you can get at the hardware stores won't hold up.

AV8TOR

I also found that you can use a short length of silicon tubing for glow fuel there too. it is just maybe a couple of inches long to handle that initial high temperature right there at the muffler fitting. The gasoline won't affect it, unless you soak it in raw gas for a while. I have also used a short piece of silicon tubing to join a short length of aluminum or brass tubing to the vent line too. As already mentioned the rubber tubing works too, just use a short length there at the vent. One issue I have with rubber tubing though is that there is the risk that some of the rubber will slough off in tiny minute particles that could get into the fuel and migrate to the carburetor causing problems. Thus I opted for short piece of silicon tubing right there at the vent.

One other thought, is if you use a brass vent fitting, you can carefully silver solder a brass tube to it, then screw it into the muffler and bend the tube as needed. Since it is only a couple three inches long, it should not be a problem in most cases.

Guys thank you for your advice, AV8TOR i am using the lines that comes with the engine. Viton, they hold much heat than regular neoprene, and don't have problems with my carburetor line; this line is far away from the engine's head, i think i can solve the problem by taking the pressure fitting as far as possible from the muffler, i include a picture of the project i am planing to do i'll appreciate any comments you have, unfortunately i cannot use any fuel line directly from the muffler viton, neoprene or tygon i guess the only line this muffler can handle it's like earlwb said silicone tubing, the one that we use for tune pipes but i don't know if this comes in small sizes like 1/8, thanks again guys for all your help.

http://www.rcuniverse.com/forum/atta...mentid=1962499

Yes they made silicon fuel tubing in many sizes from extra small to extra large. 1/8 inch should not be a problem.

Thanks earlwb i would appreciate any link to buy the tubing,

Could it be that the engine is just running too hot? Is the correct oil ratio being used, has the timing been checked? Is it being run lean?

It is not usually necessary on gas engines, but normally we do quite the reverse of what you propose. We usually wrap coils of tubing around the hottest part of the muffler to pre-heat the smoke fluid and get better smoke. Cooling the fluid (pipe/tubing) down as you want to do will hurt the quality and amount of your smoke.

I've never had problems with plain old rubber tubing hooked to the muffler smoke tap. Maybe as mentioned you are running too lean or with too little cooling airflow for the engine and muffler.

AV8TOR

The tubing is easy to get Here is one example link http://www3.towerhobbies.com/cgi-bin...bing&search=Go

As to the other comments on the fitting getting hot and melting the tubing, yes I have had the same issue myself too. Several different engines actually. But a cowled in rear exhaust engine would tend to be the worst for having an extra hot muffler.