Weber question

[iain.hamlton]

Just wondering... If you look at a weber carb, there is a hole just above the rear choke. I assume this goes into the float chamber to keep the air above the level of the petrol at atmospheric pressure.

Does petrol slosh out of here into the airbox during cornering? Does petrol evaporate through here? If so what happens if there is no airbox?
- I have always thought it a good idea to keep the standard airbox myself.

best regards, Iain

[gerrym]

DHLAs have the same hole

Gerry

[264889socal]

Iain,

The hole is there to equalize the pressure in the float bowl with that of the air entering the carburetor through the velocity stack to the throttle plate. It makes no difference if you are using a single plenum, such as on a stock Elan, or individual air cleaners, K&N style. I have seen those who in making a plate for an air cleaner forget to make the hole. The car will not run correctly. Also, if you are ramming air into the carburetor via a single plenum with a duct directly to the front of the car, the differential in air pressure must be maintained between the carburetor throat and the float bowl. And yes, ramming the air does work.

Rob Walker

[iain.hamlton]

Thanks for that, Rob. I can see how it works now. But can gas/petrol slop out of the hole back into the plenum? Can it account for the some of the float-chamber evaporation, which I suspect, compromises starting after the car has stood for a few weeks or when it's hot. (In my case, this is much better or fixed now I have an electric fuel pump, but it still takes a couple of seconds of pumping to fill the float chamber.) I am not looking to change anything. Just curious.

best regards, iain

[rgh0]

The passage from the hole goes to the chamber at the top of the jets. In very hard conering fuel can get sloshed up there and potentially drain out the hole. Getting fuel up in that part of the carb affects the air flow pressure balances to the air corrector jet and upsets carb performance. This is really only a problem on formula cars with sticky slicks and wings to create signficant downforce. You will sometimes see these cars with modifications to the tops of the webers and an extension tube raising the top cap to try to avoid these problems

Not a problem to worry about in any Elan except perhaps an extreme mod sports car of the seventies

cheers
Rohan