I just did my initial engine break in on my porch. I noticed allot of bubbles in the fuel line. The tank is wrapped in 1/4" foam all the way around. Is this normal. The engine was running a little erratic but I'm not sure if it was due to the bubbles or the cycling between 2 stroke and 4 stroke as called for in the break in instructions. It is a great planes 10oz tank. The engine is an os 46fx. The tank was full and remained level. This has me baffled. Is there too much forced air induction from the exhaust? This is the only thing that I can think of.

make sure all the fuel lines are good, did you do the underwater tank test like the directions say, also remote needle valves sometimes leak.

There was no underwater tank testing mentioned. The bubbles are from the tank up to the needle valve. They don't start between the needle valve and carb. Tubing looks to be intact. Tank isn't leaking fuel.

I sometimes get small air bubbles in my fuel lines, it runs fine when in the air so i presumed its normal...................

When you say the bubbles are from the tank to the needle, I'm assuming they continue from there to the carb. (Right?)

Did you tighten the stopper screw down really well? If it's a bit loose, you could be sucking air there. It's also possible that you have a small pinhole in the line where it connects to the tank. (It wouldn't necessarily leak fuel.)

A water test isn't a bad idea if the tank and lines are easily removed. Plug all but one line, hold the tank and as much of all the lines as possible under water, then blow into the one open line to pressurize the tank. Hold that pressure for quite a while and watch for small bubbles. (You can do it out of water too, you'd want to pressurize the tank, then wait a few minutes. If the tank maintains pressure, there are no leaks.)

Good luck,
Dennis-

Double check the fuel line. Sounds like you are getting air there. Gotta be a pinhole somewhere in the line. Change it and see if it keeps up. If not, check the clunk line too.

Pinhole is right. Couldn't see it untill I submerged it and squeezed the bottle.

with reference to this, i only see a small amount of bubbles when im filling it up using the electric fuel pump, but once ive started the engine they disappear.

Does this sound ok / normal ??

Thx

allen,
Glad you found the problem.

Dragonheart,
Don't worry about bubbles going to the tank, just those heading for your carburetor.
Dennis-

it's a good thing you caught that early. I had a simular problem on my heli engine. I replaced all of the full line and everything was fine. Also, dont bother using those GP EZ Fuel Fittings that mount to your airframe, the spring sometimes will not reset and will take in air, thus making your engine choke and couph.

An aircraft is a terrible thing to waste.

Yeah I'll bet you have to be extra careful Since u cant glide a heli in.

Who says you can't? Ever hear of Autorotation?

Just did an autorotation out of the bottom of a loop last weekend. You would think they could make those darn engines keep running when the fuel is gone. Sweet landing though.

What do mean they need fuel?


No wonder it wont start.