Recently while hovering my sceadu 50 heli it is noted that once the fuel in the main tank reaches 50% and below the header tank starts to accumulate bubble (foamy) and the engine start to rev up. The main tank is free from bubbles. Please help !!   

Thanks

Arun

Please help !! 

You have to check your clunk line in the main tank very carefully... looks like it may have a crack somewhere towards the top half.

Hi

Check that you see the clunk on the Main tank on the end of the tube.

I had mine doing same thing when the clunk came off the tube and when the tank was full it was ok and when the tank was low then the tube was passing air intermitently.

Good thing as Anwar says is to change the tube inside and check the tightness of the connections.

Anwar Ji,
I have ordered for silicon tube with 3mm outer dia and 2mm inner dia for the clunk line. Is it ok, please advice.

Should be fine.  Slightly thinner clunk lines are preferred for 3D flying, but they don't really matter when you have a header tank.  In fact, I have been using whatever is lying around for the main tank clunk line. 

And it is one of the items that seem to warrant periodic maintenance/replacement.  Some tend to elongate, and some tend to develop cracks at the mount point, because of all the movement right outside some sharp edges.

Dear Anwar Ji,
Thanks a lot.
You are right, there seems to be some crack in the clunk line towards the top. I had opened the tank and reversed the tube connections so that the cracked part is now at the clunk weight. While hovering the heli only few bubbles(no more foaming) were noted after the half tank level. To my surprise once the fuel level dropped to the clunk weight more bubbles were visible.

Thanks will keep updated once I change the clunk line.

I have changed the clunk line and still few bubbles are visible in the header tank - Is that normal ?

The tube that i had ordered 3mm Outer dia. and 2mm inner dia. seems too thin.

I have ordered for the 4mm Outer dia. and 2mm inner dia. tube which seems to be the perfect.

Thanks

Arun

The header tank should be pretty much full all the time, full enough to notice any bubbles.  Is this not the case for you ?

The header tank is full all the time. While running  the heli few bubbles run into the header tank and stays there is it normal

Kinda hard to say without seeing how bad the bubbling is.  If it is "few", it is probably ignorable.

The important thing is to verify if the bubbles are getting into the carb fuel intake.

Anwarji,
The bubbles are few and not getting into the carb. I really had a great time today on my heli. As my son is with me for vacation I am flying my heli everyday, gaining a lot of confidence. I am using 20% Nitro fuel (synthtic) on my OS50 hyper engine, please advice the low end needle and high end needle position approximately. I understand that there is no specific setting, still I did like to know how close I am.

Thanks a lot for your kind help.

Best Regards

Arun

Needle positions are dependent on a bunch of things, ranging from the nitro content of the fuel, to weather conditions, to the muffler being used. 

For this engine, the low end needle would not USUALLY need any adjustment from the default, and if needed, it will be less than 45 degrees either way from the default.  And for this engine, my experience is that the high speed needle would be between 1 and 1.5 turns, mainly depending on the muffler being used.