classic motorcycle forum

Bang on cue comes the word from Phil Beresford at Burlen:
"It (the pin hole) is an overflow outlet to prevent fuel entering the engine in large quantities if the float chamber overflows."

Further from Phil Beresford today, comes this:
"The 289/014 is a carburetter body number from a post war carburetter used almost exclusively by BSA on their B range singles. However if the carburetters are stamped 289/014 then they may have been supplied separately as the BSA carburetters would be stamped with specification numbers on the flanges."

Thanks to "R" for the photo of his fuel level which I will be happy to copy.

In downdraught configuration the pin hole is in the side of the body so its purpose may be negated. In fact it may have to be sealed to prevent constant dribbling.

Thank you for your interest.

Bang on cue comes the word from Phil Beresford at Burlen:
"It (the pin hole) is an overflow outlet to prevent fuel entering the engine in large quantities if the float chamber overflows."

I'm glad I came on here - thanks for your interest, chaps.

All the carbs are stamped 289/014. None have air holes in the base. According to information on Hitchcocks website
https://tinyurl.com/y36zdlns
"... the standard design where the primary air to the main jet and the pilot jet system comes in jointly through the main air intake, see figure 3, sheet 3 . The type numbers are 274, 275, 276 and 289. An alternative design is made where the primary air to the main jet comes in through four visible ports around the base of the mixing chamber, and where also the air supply to the pilot jet system is separate. The type numbers of these carburetters are 74, 75, 76 and 89."
There is no mention of dates.

I noted earlier that the pin hole feeds through the jet block into the volume surrounding the needle jet - see photos below.

I also noted earlier that the original heads and carbs had disappeared from the car in the 1950s. Eventually a replacement pair of the two piece copper/aluminium heads was found in deepest Utah and very shortly afterwards a serendipitous meeting with the man who had just rebuilt Sydney Allard's Steyr-engined hill climb special led to the acquisition of the AMAL 289s from that engine, which had been replaced by GP Dell'Ortos.

Thanks to John.K for the description of the pin hole with "Behind that is a through hole in the jet block that is listed as small primary air/fuel drain to prevent the engine filling with petrol when parked and the tap left on." Please will you point me to the source of that - where is it listed, please?

I am coming to the conclusion that the fuel level should be set just below the centre line of the main jet. My fuel reservoir box (baffled) will be mounted on adjustable height pillars, and, being sealed and effectively fixed to the carburetters, will maintain the fuel level under all conditions of acceleration, braking and cornering. Well, that's the plan, anyway!

Thank you all for your interest and suggestions.
I'm stuck with AMALs because that's what the car had pre-war when racing at Brooklands. It's the Batten Special with a side-valve Ford V8 engine from 1933-ish. The special cylinder heads and carbs got lost in the 1950s. I've had the beast almost fifty years and want to re-create the pre-war configuration so downdraught AMALs it has to be!

I don't understand the purpose of what is variously labelled pin-hole or air bleed. If it's important, and I assume it is or it wouldn't be there, it could be moved to another position by careful drilling of the jet block and main casting.

Thanks to John Chaterlea for the drawings - would it be possible to have a copy of the jet block drawing without the watermark? By email, maybe?

The intention is to have one "float" chamber between the two banks of carbs, but without a float - instead the level will be maintained by constant flow of fuel into and out of (back to the tank) a sealed box, always at atmospheric pressure.

Here's the car in action: www.battenspecial.com