Air bubbles between the carb and needle valve, Is it serious?

what can cause that?

We tried to open then needle valve and blow air into the muffler vent tube, it cleaned it a little bit.

From where can bubbles get into the system?

The motor is OS 46 AX

Thanks
Alex

There is a pin hole in the fuel line or the Oring of the needle valve is bad

If the bubbles are just between the needle valve and the carb and not also between the tank an the needle valve then your needle valve assembly is "sucking air" one of the seals has gone bad. There is an O-ring on your neadle valve it's self and a couple gaskets at the each of the fittings in the needle valve assembly. You can buy replacements at your LHS or from Tower.

The remote needle on my .15LA leaks air too. I plan on throwing away the remote needle and doing something else.

Beside making it impossible to tune the engine well it can cause serious problems. Air in the line causes the engine to run lean. If you're lucky it's bad enough that it just stalls and stops; a simple dead stick (if it's on take off it's not so simple). If not it can cause an overly lean run that will overheat and swell the components and scour the cylinder and either fatally seize it up or kill the compression and ruin it.

If it isn't your fuel line, you have a bad housing as stated. I had nothing but bad luck with remote needles. I will never buy another. I bought the 55AX and it has the needle back in the carb where it belongs. So far, so good, I like it. OS ate a few of my remote needle FX engines. I have a few .46 FX engines that run fine, but have had quite a few bad ones.

If you can't get it, try a K&B remote needle and see if it is the housing.

Good luck'

Thanks guys,
When I cleaned the needle valve housing by blowing fuel from the vent tube It run few moments without bubbles….

I have an idea what cause that, maybe chips from formulating the brass fuel tubes inside the tank, I guess tomorrow I’ll clean it first and place a filter.
filter is something I waned to avoid.

Thanks a lot
Alex

I know some very experienced fliers who won't put a filter between the tank and the engine on glow engines. Exactly because it is another potential source for an air leak. They convinced me to put the filters in the line you use to fill the tank, and that is what I have done for years.

Foreign material in the line will not introduce bubbles, just reduce flow. It has to be air entering between the clunk and the carb. Sometimes a bad seal at the needle valve stem, sometimes wear points in the lines at the tank fittings, sometimes bad seals of the metal tubes and fittings to hose. Sometimes vibration of the tank causes it to foam up (and the solution is to surround the tank with foam rubber).

Non remote needles can leak air just like remote needles, the difference is that with a remote needle, you can see the problem but with a non remote needle the problem is not visually obvious. Just because you can't see the bubbles, it dosn't mean the problem doesn't exist.

OH NO Thats an OS engine, It can't be having a problem.[X(]

Had the same trouble with my Evolution .46 and as a student I was having a heck of a time with continous deadsticks. Almost hated to fly, I would think I had it fixed and it would come right back. Replaced all the fuel lines..thought I had a pin hole..Deadstick...Finally I descided to take the motor off and break it down. Their on the bench I realized that the nipples for the fuel line from needle to carb were loose and that their gasket was coming out..Replaced gaskets and tightened the nipples...Problem solved. I learned a valuable lesson... After every few flights I will inspect each and every screw, nut, bolt, coupling, etc...

This happens with a LOT of engines where those heavy stock paper washers are used.

Also cap screws on a new engine tend to get loose after the engine has been run for a bit.

It's a good idea to tighten everything down carefully on a new engine, after it's first tank or two.

You'ld be surprised at how often the cylinder head is loose on broken in engines.

Don't fear using a filter. They are worth more than they cost. And darned it almost anyone can install them securely. And if you then look in them every so often, you might catch a problem before it happens. It often amazes people who find stuff in them. But the people who know those people usually aren't amazed. Their insurance value is worth more than the effort to use them.

The other day, a guy who has a filter in his fuel tank dropped his fueling line on the ground. He was a big one about telling everyone he didn't need a fuel filter on the engine and that nobody did. Hey, stuff happens.

Fuel filters from now on.

Thanks,
I’ intend to run the engine outside of the airplane to see where the air bubbles coming from. As more I think about it I don’t like the easy Sport 40 to begin with

I decided to avoid filter and put the needle up straight in order not to put it through side of the fuse and as I’m looking at the easy sport, it’s too tight behind the motor and to put a filter there would be an engineering challenge.
All this operation would require to get the motor out and if I’m already doing it I might as well put it on a new plane….
So I ordered another midstar kit that will fly with the current accessories and filter!
current flying season is over as I look at the weather outside.

Thanks
Alex