I’m helping a new member of our club (PWA7 Staffs/Shrops) with his 1936 ARR Ruby that he bought earlier this year. I have no previous experience with a Ruby or its Zenith 26VA carburettor. I have rebuilt the engine and it started first time using the choke. However, from slow running it will not pick up cleanly using the throttle to a faster running speed: it gasps for air as you attempt to open the throttle just like a huge flat spot! When the throttle is opened very slowly it will attain a higher speed.

One problem is that the car has not run properly for a very long time so the carburettor is not a known good working example. I have stripped it totally several times but with no improvement. It has all the correct jets which are all clean and I have cleaned the little Progression Jet underneath the inlet tract together with the small airways leading to the engine side of the butterfly and fitted a screw plug to the Progression jet access which was missing. I have also checked and blown through all the ducts from the beak to the float chamber and had the Emulsion Block apart.

The timing was set to TDC to start with and advanced a little since. The slow running is good and seems to respond correctly to adjustments of the air screw. The air screw is about one and a half turns from right in. I have tried altering this setting but it has no effect on the flat spot. I’m stuck!! Any helpful suggestions will be greatly appreciated.

Location: Stafford

Hello Bryan. I've been playing with 26VA's for the last 40 years and they are still a mystery to me - flat spots, dripping after use etc, etc.
If you would like to give me a call on 01785 850 916 I could loan you a couple to try - but after the weekend as my son Chris is getting married on Saturday and I'll be a little preoccupied.
Regards
Stuart

Location: Staffordshire, the creative county

Am I being naive or does this smack of fuel starvation?
I suspect it is not gasping for air but gasping for fuel and further suspect a partial blockage somewhere between petrol tank pickup pipe end and caburettor, (- more likely the tank end).

Steve V.

Location: Polegate, East Sussex, United Kingdom

Might even be the wrong carb, they were used on other vehicles so if you have one with a larger choke than an A7 what would appear to be the correct jets will be too small. This will give the symptoms you describe, as will fuel starvation and and air leak.

Location: Auckland NZ

There should be a number 7 stamped in to the flange where it bolts up to the manifold. The 26VA was also used in the Austin 10, with 10 stamped on the flange. They are subtly different.

Location: Gard, France 30960

Over the years I've messed about with a few 26vas.
What I have found with nearly all of them is that the air screw (slow running) has to be almost closed to enable the engine to pick up satisfactorily from tickover.
Edit. Have you checked the secret jet under the carb?

Location: Bonnie Galloway

Brian,
I solved this problem last year on a friends Ruby by simply exchanging the
compensating jet from a standard 50 to a 60.
J

Location: As far east in Kent as you can get

I posted this solution a while back on an other thread:

'Engine dies when throttle opens'

Turned out to be the air regulating screw (what some refer to as the slow running needle). By unscrewing it just 1/4 of a turn the throttle response came back to normal with instant pickup. Yet it made no discernible difference to the quality of the idle. Never knew the screw has such a marked effect on pickup.

(For clarity - That is 1/4 turn from fully screwed down)

Location: North Herts

Good morning all.
There is not necessarily a number 7 stamped on the flange - I have a number here which are Austin 7 carbs but without the number. The criteria is a 17mm venturi, this is cast into the orifice behind the choke flap and mechanism.
The Austin 10 used 19,21 and 23 venturi although I do know of enthusiasts who use the 19mm carb on their Sevens but I don't know what size jet combinations they use.
Regards
Stuart

Location: Staffordshire: the creative county.

Thank you all for your very helpful suggestions of things to check. Also, thank you to Rurairidh for your most helpful telephone call. Furthermore, an even bigger thank you to Stuart for loaning me two (yes two) carburettors to try.

Well, Stuart’s first loan carburettor worked perfectly so the fault is with the original carburettor which has (I’ve checked) all the correct jets and it has 17mm choke tube and looks identical to Stuart’s loan carb.

I will now refit the original carburettor after checking again that all the jets and airways are clean. I will, also, adjust the air screw as suggested. I will let you know how I get on!

Try another float bowl, other posts on the forum have indicated that the bowl needs to match the carb body. When I had fuel dripping and hesitation on pick up as you describe I swapped the bowl for another from my "never throw anything away box" and it seemed to cure the faults. The replacement had a different bowl to the original. Why the original one should suddenly develop an annoying fault I have no idea. S.ds law I suppose.

Location: flat Norfolk fens

As previous, many similar Zeniths have a gasket. With age the bowl and lid distorts, bubbles etc so air leaks past the idle needle valve.

The internal differences of the two variants of 26VA raised in Oct 2015 never was explained on the Forum. Someone must know or be capable of fathomimg. This may be an appropriate place for the explanation

Location: Auckland, NZ