Differences in Solex Carbs (Herald)

[Colin Lindsay]

I'm used to the standard BP30 PSEI Solex carb for the Herald 1200 but they're getting rarer than they used to be and certainly more expensive, and I like to have the odd one as a spare just in case.

I recently opened a box of spare parts and found a complete carb, but with differences to the Herald variety. I think from a check on the Net that it's a BP30 PSEI-6. Both this and a confirmed Herald model have the same size manifold flange, and the same size of intake, so I'm assuming it would fit a Herald if necessary, but there is one large difference to one side, this triangular protrusion that is missing from the Herald version. All other attachments, levers and rods are the same.

Does anyone know the subtle differences - is it a larger carb, improved, better cold starting, more refined, or is it totally unsuitable for a Herald? I know the Herald version is adequate but basic, so is there any benefit in using something like this at all? Herald carb is to the right in top photo, and lower in the other.

 

 

[Casper]

The 30 refers to the aperture and you can re-jet it using stuff from your parts stash if necessary.  Although the stranger seems to have the usual choke arrangement, the extra bit looks rather like the choke arrangement on the earlier ZIC carb.

C.

[Pete Lewis]

most triangle shaped valves are economy devices to avoid excess fueling  commonly called econostats

http://zenithcarb.co.uk/economy-valve-cover.html

Pete

[Pete Lewis]

rimmer show it https://rimmerbros.com/Item--i-RH5206

[Colin Lindsay]

Thanks Casper and Pete. I was thinking this was a more hi-end carb that would improve the Herald's running (eventually!) and can replace jets etc with OE Herald versions; I was also waiting for the message that started "why?"   It may turn out to be an unnecessary or pointless fitment but it's there... and I'm wondering... you know how it goes.

I've just read a bit about the Econostat and it's designed to allow the carb to run on less fuel but still retain performance... the main jet in many applications had to be quite large for top-end driving and therefore was over-large for lower speeds, so this allows for a smaller and more efficient main jet, reducing low speed richness but maintaining performance when the speed increases.  

You can also buy jets for use between 6000 and 10,000 feet, and above 10000 feet, where the fuel mixture would be affected by altitude. At least, you could if they were still available.

[Pete Lewis]

Well they save around 4 mpg  so with a dizzy vac unit and econostat  and heavy throttle spring  every week the tank will overflow

Pete