SU Carburettor Conversion

[Mike Costigan]

A side-draught Zenith and gravity tank doesn't work in Derbyshire! No doubt it works fine in the flat lands of eastern England, but I used to find I needed a head of at least one gallon in the tank to keep things flowing in the Pennines.

[Ruairidh Dunford]

I have seen set-ups like this both work and not work - resulting in a pump being required.

Clearly different cars (and set-ups) work differently, perhaps try without a pump and fit one if it becomes necessary?

[Paul N-M]

Or pressurise the tank. Very period. 1 to 2lbs is all you need.

Paul N-M

[bob46320]

thanks gentlemen for your replies, any photos appreciated.
Bob

[JonE]

oooh- that sounds good! something else on the dashboard!

[Nick Mayne]

I would like to widen this discussion hoping someone (maybe a special builder) can advise me. I have an engine with John Barlow crank and rods, pigsty sports profile cam and followers, larger inlet valves, a high compression head and an SU HS2 1.25" sidedraught carb. As the dashpot is normally at 30 degree to the bowl but I had to have it upright, I tweaked the bowl float so am sure that the level is below the carb bridge. I have a number 4 needle and standard .090" jet. and 'hard'plugs. I was running so rich (10 mpg!) that Oxfordshire Sevens took the engine apart and found the excess fuel had washed the oil off the bores and they had become glazed. A re-hone and new rings hopefully put that right. The theory was that the pancake air filter had caused excess richness so that is now taken off. However, the engine still runs very rich with wet plugs and at 3000rpm the dashpot only lifts about 1/4" off the bridge. I do have a 'blue' damper spring and the correct SU/Burlen oil in the dashpot. The jet is high up and maybe a mm below the bridge so not much scope there.
There is also an intermittent miss at all engine speeds. Originally I had the carb and timing set up on a rolling road so I have been reluctant to change that yet.
Advice from someone with a similar spec engine and SU carb would be much appreciated. I cannot see how to add a picture of the layout on the forum.

[cardiffrob]

I had a persistently rich engine, despite the correct needle'jet etc.  Eventually it started to flood and I twigged that the float was nearly full of fuel.

Have you tried changing the float shut-off height to keep the fuel level lower in the jet?  I wonder if that might help?