Ok I checked everything, no leaks or loose fittings etc. The engine runs fine but at full throttle I see a constant stream of bubbles in the line feeding the carb[X(]. Is that normal?
It only does this at 3/4 - full throttle.

Boy I cant stress enough how important preflight checks and test are. I had a wheel fall off from vibrating loose. Would of made for a real interesting landing considering its a tail dragger.

Hi cj Have you checked to see if your carb is seated down tight on the 0 ring and the screws tight? Did you pressure test the tank also? Bob

The bubbles are not likely coming from the carb, more likely coming from the lines from your fuel tank. Replace them - its hard to "see or check" if there is anything wrong with the lines unless its a big hole. You don't want those bubbles - it acts like leaning out your engine. Could cause engine to quit when you don't expect. It makes it harder to tune properly. I have had the exact problem. You might also try putting on a small plastic strap around the fuel tank ends.

Sealed engine , muffler, and carb fittings with red rtv. No leaks! Ran full tank through and no feul on engine at all.

The tank is a 3 line , all new lines and all tight, pressure check ok.

third line is fill line with a screw in it . Bottom line is from clunk to carb, and clunk is on bottom in corner of tank. Left line goes from muffler to a 2 inch alluminum tube through the gromet into the tank . Same for right line to fill tank. There is no feul tubing from the right and left fittings going into the tank just the 1.5 inches of aluminum tube.

No airbubbles till i hit 3/4 to full throttle. Its got me baffled, high rpm smooth even moving nose of plane up and down at 45 dgree angles.

I have always had bubbles in my glow engines.
Unless it is effecting the engine I would not worry about it.
If all else fails, squirt a single shot of armor all in your fuel bottle and shake well.

Heres a pick of the line setup.

Armor all in the fuel ??????

Still sounds like air leak some where, try pulling out the tank emty it real good, and check with some dish cleaner soap all around the fittings, lines etc. then try blowing check for bubbles that might be forming

you might want to put a clamp arround that screw

Check and see if the tank has any cushining around it. I had problems with the same thing in my nexstar and we put a piece of close cell foam cushining the tank and it went away and I have to check it every so often.

Just thought of something [X(] Maybee fuels foaming alittle from vibration

If every thing else checks out ok then its vary possible

Yes, fuel foaming from vibration, very common. Armor All was an industrial strength de-foaming agent, before someone "discovered" it made a mess of all things vinyl......
Just use A DROP OR TWO. Or a VERY LIGHT shot from the pump bottle. If you don't want to buy a bottle, go to the local auto parts store, and they should have little "wipes" or sample packs of it, a lot cheaper than a whole bottle........JUST A DROP OR TWO!!!!!!

Jetts

It is probably the screw. What size of fuel line - it could be the wrong size. Bubbles aren't good, you really should try and get rid of them.

Cool idea jet star ill try it. As for the screw if i pull it while engine is running it pumps fuel out from exaust pressure. when its in there is no leak so I dont think its allowing air in but ill try a solid rod plug tommorow. After thinking back I didnt notice it till the engine had been running for a while so the fuel was getting down around half or less so im betting on foaming fuel.

I want to thank everyone here for the help you give to all . It really makes this hobby enjoyable.

Sounds to me like you have a vibration problem, because you say the bubbles show up at full throttle. Make sure the prop is balanced to reduce any excessive vibration. Isnure the tank is wrapped in foam. Just make sure it is not packed too tight, just enough to isolate from the airframe. Last option would be to put an in-line fuel filter between the tank and carb. These filters help remove air bubbles as they hit the screen.

Hope this helps. Nothing worse than an engine going lean due to bubbles.

All I needed to read was the first few lines to guess OS with the rear needle. Some of those things produce their own bubbles at the needle. Have no clue as to why. I went through a couple 91 FX engine and never got them to work. Some guys are putting fuel line over the needle to the housing to stop it. You can also try a K&B needle to see if it solves it. Make sure the bubbles start at the carb before playing with it there. If there are none coming from behind the firewall and they start at the remote needle, then the problem is there. I found it easier to just go to an engine with the needle in the carb where it belongs. No more problems.

Good point about the remote needle. ( I won't own one because of problems like this - just another failure point) Still recommend that fuel filter. It'll go a long way to reduce those bubbles.

WHOA! I posted too quick. According to the pic at post 6, this is a carb needle, not a remote.

Still good advise for remote needles though.

Oppps, I should have blown up the picture. Looked like a remote when I looked at it. The third line you have looked like a line to a remote needle.

That changes things. The bubbles in the line have to be coming from the tank then. Sorry about that.

Make sure your tank is not jammed in the fuse too hard with foam. If it is mounted too solid, it will produce the bubbles you are seeing. I have a friend that had too much foam around it and it was too tight. That was the same as not having any foam. Huge bubble problem. Check that out.

Had 1/2 foam rubber and it was real tight. Pulled it out and checked everything carefully. Used 1/4 foam padding this time and test ran. No bubbles till it ran outa gas. Problem solved. Thanks guys , great help as always.

You used less padding and it worked?
Maybe you didn't secure the tank as tight the second time.
Less padding doesn't make sense.

I too have seen this happen when the padding is over-stuffed around the tank. The foam actually transmits the airframe vibration straight to the tank and causes bubbles.

Sure, Too much foam, causing vibration to be transmitted, = foaming=bubbles.

Jetts