calling ken ct

[ford1]

ken, is there any way to put a relief vent on top of the carbs, like the ones on some carbs from the 60's, it was a small hole on top of the carb with a flapper tied to the throttle contron on the carb, when driving the flapper came down and coverd the hole, when you shut the engine off the flapper would open and bleed off the pressure built up in the carb from being hot so it wouldnt force fuel thru the jets into the engine from the pressure of boiling fuel, i remember seeing them but cant remember which carbs used them

[Henry/Kokomo]

I believe Rochester 2G's and 2GC's have that arrangement. Never saw one added to a carb. but I'm certainly no expert.

[52merc]

bill put it on chevy barn hes on there all the time trev

[ken ct]

Originally Posted by ford1

ken, is there any way to put a relief vent on top of the carbs, like the ones on some carbs from the 60's, it was a small hole on top of the carb with a flapper tied to the throttle contron on the carb, when driving the flapper came down and coverd the hole, when you shut the engine off the flapper would open and bleed off the pressure built up in the carb from being hot so it wouldnt force fuel thru the jets into the engine from the pressure of boiling fuel, i remember seeing them but cant remember which carbs used them

Never heard of it being done,not even sure what your talking about,sorry. ken ct. ps im on this ford barn a lot more than the Chevy Barn.

[JWL]

Which carb will allow pressure to build in the float chamber? How can atmospheric pressure push the fuel out of the discharge nozzels if the chamber is sealed and not open to atmosphere????

[BUBBAS IGNITION]

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Actually all carbs float bowls are exposed to the atmosphere, that what makes them work.
The stromberg 97 is vented thru the pump rod and the 94 has a internal vent.
Typically is fuel is pushed outward the float is too high etc or some other problem.
Bowl vents were added in later years for emission reasons, the epa didnt want raw gas exposed with the engine off.

[40 Deluxe]

Early Holley 94's were already vented to the atsosphere through a hole in the side of the accelerator pump "tower", in the air horn as illistrated by Bubba's drawing. Later ones had an internal bowl vent, a tube placed diagonally in the carb throat angling down in the float bowl. I believe the closable vents you mention came out about 1957, with the new style Holley and Ford carbs, and continued throught he late '60's-early '70's when emission regulations changed everfything. These vents were opened at idle by the throttle arm and closed by a spring off idle. Internal venting offered better mixture control. Ater all, fuel is pushed through the jets into the discharge nozzles by air pressure above the fuel in the bowl, which pressure is higher than the pressure of the air flowing through the venturi. If the air cleaner is restricted, an external bowl vent will result in an excessively rich mixture while an internal vent largely eliminates this effect.

[JWL]

Well, at least 2 people understood my post. Unfortunately, not the original contributor. It can be very helpful to understand the inner workings of the various systems on our old cars.