El Poncho

Hi Guys,

Just need some advice on a problem i have with my world model trainer.

I have a OS55 glow motor fitted to this machine and there is constant air bubbles in the fuel ine to the carb. Why is this and how do i correct this? Someone told me that is could be that my propeller is not balanced an dthat this is causing vibration on the plane.

If this is the case how do i balance mu prop?

Mk23socom

My Feedback: (7)

You could use any of these!

http://www3.towerhobbies.com/cgi-bin...?&I=LXK247&P=0

http://www3.towerhobbies.com/cgi-bin...?&I=LXD712&P=0

I bought an old toolbox a couple years ago and it had the fingertip balancer and I dont trust how that works. What I did to still be able to use it was to place the prop in the device and set the shaft on two glasses of identical size.

To balance a prop that is Nylon or G/F Nylon, you want to lightly sand or file the heavy end until the unit is balanced. A wood prop I believe my dad has used some kind of lacquer clear coat on the LIGHT end and balanced his props that way. Someone with experience in that area will surely chime in.

I have also used the other product I have listed and am very happy with it as well.

You might also look at all your fuel lines and fittings to make sure everything is tight and the fuel tubes are in good condition. This includes pulling the stopper and inspecting the clunk line as well. Also check to make sure that all the fuel lines are hooked up correctly, sometimes in haste or late at night when one is tired, you can inadvertently hook things up backward. When you get out to the field, you cant get your stuff to run right and you puzzle and puzzle over why all that time last night making sure things were right are netting you no results. With further inspection, you find that everything is messed up for one reason or another. But it's NEVER happened to me.

jetmech05

are the bubbles coming from your fuel tank...or do the bubbles start at the needle valve?....If from the valve you may need a new o ring at the valve....If from your fuel tank is the tank wrapped in foam...it should be

Gray Beard

My Feedback: (-1)

Sounds like a hole in a line or a loose bung. When I assemble a new fuel tank I plug the breather line then hold the tank under water in a sink and blow realy hard into the main line and look for bubbles. This tells me if the pressure, main line and bung have no leaks. The main line may also develope a leak on the inside of the tank but for that the tank has to be taken apart. Your local hobby shop will usually stock extra bungs and it's always a good idea after taking a tank apart to replace the bung with a new one. If a plane/tank has been sitting around for a long time it is a good idea to re-line it. If it isn't the tank you may have a leak in the O-ring or the screws holding on the carb. The tank is usually the first place to look then start looking at different things.

cutaway

Add to a list of possible causes:

Microscopic lengthwise cracks in brass tank tubing that develop over time. Its not a high frequency issue, but it crops up occasionally. Al & Cu tubing seem not prone to this.

As mentioned above, remote needle O'rings are prone to leaking air. I have also seen remote needle barb fittings that were loose or not seating well leak air.

Carbs and remote needle assemblies that use a banjo fitting can leak air if not tight.

Crudely sawed and undressed metal tubing ends are prone to cutting fuel line tubing and causing air leaks. This is a very common problem when someone was in a hurry.

Tubing cutter cut tube ends raise a small ridge at the edge of the tube that eventually can nick silicone of not smoothed off. silicone tubing is very very nick sensitive.

acejinx

I had the same problem, after a bunch of frustrating flight I switched ENGINES. Same problem. I don't know why it started at the needle and not at the tank, but once I put a bunch of that vibration absorbing foam around the tank it went away.

El Poncho

Thanx Guys,

I replaced the fuel lines and the bung over the weekend. There is still some bubbles but dont know if that is causing the dip in the motor output.

I will adjust the air/fuel mix on ground and it will rev fine. After a few seconds in the air you can hear the revs dropping and the motor revving up and down even though its its on full throttle.

What can cause this? I am getting very frustrated now.

jetmech05

well if you have bubbles in the fuel line you'll never get ti tuned correctly...and the revving sounds like a tunning issue...is the tank wrapped in foam?