Hi all and sorry if the answer to my question will be obvious to most of you !!

I'm a 'returnee' to stunt and not that clued in to 'uniflow' tank technology.

Just got back from our club field [ in S.W.France by the way ] and just couldn't set the needle on my Brodak 40.
It normally is faultless and holds it's needle just great. It kept leaning out . Tried different fuel , new fuel tubing and a different uniflow tank as well.

My principal question is : Should I see air bubbles in the fuel tubing between the uniflow tank and the NVA?

Again , apologies if this is obvious to you experts .

My Brodak was carefully run-in , and was using an 11x5 APC which has always performed well in the past.
The weather was hott'ish and very humid.

Any advice would be gratefully received.

Thanks in advance ,

Robin [ British ex-pat ]

 

Thanks for that Jim...... I was using a 2 oz uniflow Brodak tank . No muffler pressure .
Side mounted on a profile fus . I suspect [ and only suspect ] there was air coming in via the bottom overflow which was capped , but the cap was a ' loose ' fit so to speak. 
I've  now tested all my uniflow tanks for leaks and they're all O.K.
Odd !! Going to flight test again with my other uniflow tanks and hope for the best .
Anyway , good of you to come to my help ....thanks.

Robin

p.s.The Brodak's a beauty once run-in. Highly recommended.

   A couple of things to check are the prop balance - it could of been nicked,  and the overflow
vent cap must be good  - it cannot leak - not at all.
Also, look for something loose, like the motor mounting bolts, backplate bolts, headbolts.
It's also a good idea to mount the tank against a piece of foam rubber. 

Good Luck,
   Stan Bidowski

Thanks guys for the advice. Very much obliged .....

Robin [ in a damp and rainy France ! ]