New comers, this started out as a simple bubble in the fuel line issue onto the Uniflow tank an so on.... New topic starts on page 3, from there you will understand where this post has gone....

Okay I am new to Nitro so bare with me.... I have a Nexstar Select that I flew a few times with a OS .46LA an it seemed really weak, my electric version performed better... So, I bought a OS .55AX broke it in on the stand... (the quick run to temp shut down... over an over till I had about 15-20 min run time then ran a about 4 tanks threw it moving the throttle as i would be flying not going over half throttle.) on the stand it worked fine an would run the fuel tank dry... installed in plane an now i am having issues... notice bubbles in the fuel line going to the carb (clear) the longer it runs there is more an more till it get to many an dies... So, i replace the fuel tank with the one i used on the test stand.... Same thing happens but this time I notice the green line coming from the exhaust it seems to be pushing lots of air into the tank creating the bubbles... (well I just read this is to pressure the tank so that not it) basically it starts as bubbles then it is strait air an there is no fuel in the fuel line (to carb)...

What is going on here? a seal on the engine? what could be causing the fuel line to get bubbles then run the line dry?

There's two possible sources of bubbles in the fuel line: One is vibration which is frothing the fuel in the tank. The way to eliminate or reduce this is to balance your prop (assuming it's causing vibrations) and surround the tank with soft foam.

The more usual source is an air leak in the fuel line. The favourite place is where the fuel line goes onto the brass tube going into the tank. Nicks and holes are very difficult to see, so you need to flex the line to reveal them. Many a time I've given up looking, and just replaced the whole line to be sure.

When you say more bubbles appear as the engine continues to run could mean there may be a couple holes in the carb line inside the tank itself. As fuel draws down unovering a second hole you get more air.. The pressure coming from the muffler will not add bubbles.. its forcing air into the tank pressurizing it a bit. The air in the fuel line is not related.. MY LHS sells thick and thin wall tubing with the same Inside diameter. I always get the thick for extra insurance.

Hum, okay thanks for the information.... I was hoping by replacing the fuel tank that it would of eliminated the possibility of holes in the fuel lines... I have 1 more new tank that I will try (3rd tank) lets hope that's it.

I apologize but I don't understand your comment. How would replacing the tank l eliminate holes in the fuel lines? I doubt the tank is the issue, especially if your using new ones... I've had tanks for years and they just don't wear out under normal use..

I'm assuming your using one of the dubro type poly/plasticy type soft tanks and not a metal one?

Replace ALL the fuel tubes, INCLUDING the one between the needle valve and the carb. There IS an air leak in one of the tubes. The tank is not the problem.

silicone fuel line is VERY nick/cut sensitive - i.e. prone to pinholing when slipped over metal tubing that was roughly cut and the ragged ends left undressed. The factory tubing ends on almost every tank kit are rather sharp and should be chamfered with some 400 grit sandpaper before use.

Originally Posted by Thermalin

I apologize but I don't understand your comment. How would replacing the tank l eliminate holes in the fuel lines? I doubt the tank is the issue, especially if your using new ones... I've had tanks for years and they just don't wear out under normal use..

I'm assuming your using one of the dubro type poly/plasticy type soft tanks and not a metal one?

Originally Posted by Fokker DII

Replace ALL the fuel tubes, INCLUDING the one between the needle valve and the carb. There IS an air leak in one of the tubes. The tank is not the problem.

The tank I replaced it with already had fuel lines on it thus "different" fuel lines... as mentioned the tank I used to replace the old one was the tank I used to break in the engine on the test stand... That means it at the time of testing had proven to be a good tank an good fuel lines, kinda eliminating both possibilities at the same time by using a "known good tank an fuel lines"... yes the possibility the tested tanks fuel line has a small hole now.... I have a fuel pump an when plugging the 2 hoses an the adding fuel threw the fueling line i don't see any leaks (kinda pressurized by the fuel pump) I will try balancing the prop if that does not work I will replace the fuel lines... By the way this setup has 3 lines one going strait to the muffler, the other to the carb an the fueling line.

It will cost you a dollar to put new fuel lines in, just try that first.

I Have had needle valves that leaked air down the threads. If all else fails, cut a short piece of fuel tubing and force it over the threads so it seals the point where the valve is threaded into the tube.

Les

it seems to me that if the tank is pressurized by the muffler then the only place to get air into the fuel line would be the pickup line in the tank that is not submerged, or at the point that line connects to the brass tubing inside the tank. any other holes would leak fuel, since the line is under pressure.

Originally Posted by sweatybetty

it seems to me that if the tank is pressurized by the muffler then the only place to get air into the fuel line would be the pickup line in the tank that is not submerged, or at the point that line connects to the brass tubing inside the tank. any other holes would leak fuel, since the line is under pressure.

You would think so, wouldn't you? But my experience is that a leak anywhere in the line, usually outside the tank, where it goes through the firewall, or where it goes onto one of the brass tubes, will cause air to get in.

Originally Posted by abenn

You would think so, wouldn't you? But my experience is that a leak anywhere in the line, usually outside the tank, where it goes through the firewall, or where it goes onto one of the brass tubes, will cause air to get in.

I have had More than One time when a pin hole showed up between the needle valve and the carb. It ALWAYS sucked air, never leaked fuel. from that or any other hole in the tubes. If you won't change the tubes then so be it.

Originally Posted by LesUyeda

I Have had needle valves that leaked air down the threads. If all else fails, cut a short piece of fuel tubing and force it over the threads so it seals the point where the valve is threaded into the tube.

Les

Les,that suggestion has cured more ills in a fuel system,than any other fix....
I've had needle valves so loose you could see them vibrating,and the fuel line segment cured all that.

Originally Posted by kylerdinger

It will cost you a dollar to put new fuel lines in, just try that first.

Originally Posted by LesUyeda

I Have had needle valves that leaked air down the threads. If all else fails, cut a short piece of fuel tubing and force it over the threads so it seals the point where the valve is threaded into the tube.

Les

Originally Posted by sweatybetty

it seems to me that if the tank is pressurized by the muffler then the only place to get air into the fuel line would be the pickup line in the tank that is not submerged, or at the point that line connects to the brass tubing inside the tank. any other holes would leak fuel, since the line is under pressure.

Originally Posted by abenn

You would think so, wouldn't you? But my experience is that a leak anywhere in the line, usually outside the tank, where it goes through the firewall, or where it goes onto one of the brass tubes, will cause air to get in.

Originally Posted by Fokker DII

I have had More than One time when a pin hole showed up between the needle valve and the carb. It ALWAYS sucked air, never leaked fuel. from that or any other hole in the tubes. If you won't change the tubes then so be it.

Originally Posted by epoxyearl

Les,that suggestion has cured more ills in a fuel system,than any other fix....
I've had needle valves so loose you could see them vibrating,and the fuel line segment cured all that.

okay guys... this is what I did today. balanced a new prop an installed did not fix. Took tank out an plug 2 lines blew into the other, yep a hole in a line, replaced an did it again, another hole in another line, replaced blew in it again did not see any holes... installed tank an it seemed to run longer but same thing happened again, the fuel line ends up getting bubbles an going dry...

Bare with me on this project guys.... I work nights an 13-14 hours a day (an a 5 week old baby) so only have like an hour or so a day to try new things. Sunday is my only day off an will be able to do more....

So, i plan on replacing the last fuel line (all 3) with dubro fuel line if that does not work what else would it be? (all i have is yellow fuel line so sunday i will get color codded line..

Thanks
Jo