I have not read all the responses to your problem. However here is what you need to do.

1. Pull the tank.
2. Pull the stopper and replace the fuel pickup line. Ensure when you cut the new tubing that you cut it with an X-acto knife. DO NOTUSEWIRECUTTERS!!
3. Re-install your stopper and make sure it is snug. Make sure the clunk does not touch therear aft sideof the tank when it is held upright.
4. Replace the external lines using an x-acto knife to cut the lines. Roll the fuel tube under the knife for a straight cut.
5. USEFOAM around your tank, and re-install your tank and hook up your lines.
6. Balance your propellor. (excessive vibration causes foaming inside the tank which will lean your mixture.)
7. Run your engine and check for bubbles.

All the above take into account that nothing is wrong mechanically with your engine. Make sure your carb fuel fitting is snug. Go fly.

Glenn Williams

It's been so long sense I have seen a fuel foam from vibration I can't even recall when it was. The anti foaming agents work that well. There was an address for a video from Germany but it is no longer up. They have a tank hard mounted on the outside of the fuse with a camera on the wing pointed at the clear tank to show what the fuel is doing during different stunts. A true eye opener. Throughout the whole flight not one bubble in the tank. Foaming just isn't a problem these days. I just happen to have my favorite flying model with the canopy off today so I can replace the battery. Here is a photo of the tank. It's hard mounted over the CG. The plane is a CG Extra with a YS 1.20. Never even a hiccup from foaming or vibration. I have 5 other planes in my shop with the tanks hard mounted like this. I wouldn't risk any of them if there was a foaming problem and the fix was just some closed cell foam. Fuels have improved over the years and foaming is a thing of the past. A tank/line problem is something that still happens all the time and bungs don't get tighter with age.

I did crash the engine before I put it in the current plane. Do you think I should take it loose and check the bearings or is it another way of checking without take it loose?

No bearings in an LA, it has bushings. You may want to take a look at that plastic needle valve assembly to see if you have a crack. In a crash the clunk often is pushed to the front of the fuel tank and gets stuck in some odd angles like forward and up. That happens all the time. It really does sound like an inside of the tank problem though. If it was a needle valve problem it would be a problem right from the start. Sounds like the engine is just running out of fuel early at some point. Checking the tank only takes a few minutes. Get off the computer and go look!!

To the OP a question. What is the orientation of the engine on the plane? Is it straight up? or laying on its side? The reason I ask is simple. IF the engine is mounted upright the carb may be above the level of the tank. If this is the case it may be having problems drawing fuel thus the air bubbles. IF the engine is laying on its side then I would be checking fuel lines closely and maybe the tank plug is not tight enough and it allows air to enter after a few minutes of flight.

as soon as I seen OS LA series id say change the engine...hehe...then fix the real problem

I have a plane that gave me trouble for the first 2 years. Kept fighting it, replaced all the fuel lines and it did not fix the problem. I was about to give up on the engine. I improved the problem by rotating the engine 90 degrees to lower the carb needle relative to the fuel tank. Everytime I got the plane inverted, the engine would flood out. The engine mounting rotation helped solve the flooding in inverted flight, but not the stalling. I finally tossed the (cheap) tank that came with the ARF and put a DuBro or Sullivan (I can't remember which) and the problem was fixed instantly. Now the engine never, ever stalls, unless I do the throttle cutoff from the radio.

Just a question concerning an earlier answer, how can the fuel tank stopper or bung or plug or whatever you want to call it, even if it IS leaking, cause bubbles in the fuel line between tank and carb ? Fuel leak, little or no tank pressure I can see. Just curious as to what experience occured with bubbles in the tank to carb line that could possibly be solved by fixing a leaking bung.
Thanks for any replies.
Dan

OP,
if you crashed the airplane or had a hard landing, the clunk in the tank may have been lodged in the top corner of the tank. Once the fuel goes below its level, the engine quits. Its a good thing to check

Ameyam

Not meaning to hijack this thread, but can someone explain to me why you can't cut fuel line with a pair of side cutters?

Its highly likely that its for the same reason 'They' will tell you should not be cutting off the long end of your propellor at the field with a pair of dykes either, probably not gonna be too purdy and square.

Hmm field expedience trumps purdy.


John

Like John said, it just won't be all pretty and such. But other than that there isn't any reason that I know of to not use cutters. I've done it dozens of times at the field (and even a few times on the bench when the cutters were easier to get to than the knife) and I've never had any issue come up because of it.

Ken

OK, that makes sense. And what a relief. I thought maybe cutting my fuel lines with a pair of dykes was what was making me such a lousey pilot.

And John, would "they" prefer you cut the short end of the prop?

Aw Dang, that makes my little pilot guy all grumpy when his head falls off and rattles round inside the canopy.

i mix my own fuel, just castor oil and methanol, i also hardmount all of my tanks, my fuel never foams (or if it does its not a problem at all) so the "antifoaming agents" manufacturs put in their fuels solve a problem that isnt their (or they just dont put anyhting in the fuel to begin with)

either way if your fuel is foaming you have a bigger problem than foamy fuel....maybe a out of balance engine or something.....or you just have a huge engine that shakes your plane like crazy