1974 C10 Quadrajet, What Are These Vents?
 

Hello everyone.

I got my 1974 c10 to run and drive for the first time in 10 years.
It runs pretty good. The only problem now is that when you pump the throttle, fuel comes out of this vent on top of the carb. Ive only tried this with the engine off. This only happens when you pump the gas. I think the fuel from the accelerator pump is leaking through a gasket. It did flood out the carb and make it hard to start later that day. My question is where does this vent go?
I don't believe the quadrajet on my 1972 has these two vents. Once I get the new exhaust installed, I am hoping to drive it 15+miles to the carb shop, if this fuel leak isn't too serious.

Thank you.

Re: 1974 C10 Quadrajet, What Are These Vents?
 

According to the ROCHESTER CARBURETORS manual the vents are part of the Accelerator Pump System, During high speed operation, vacuum exists at the pump jets. A CAVITY beyond the jets is vented to the top of the air horn, outside the carburetor bores. This vent acts as as a suction breaker-when the pump isn't in use, fuel won't be pulled out of the pump jets into the Venturi.
When the throttles are opened rapidly for acceleration, airflow and manifold vacuum change almost instantaneously. Because fuel is heavy and lags behind airflow, a momentary leanness results. The Accelerator Pump supplies extra fuel for smooth operation during this condition.
Straight out of the manual ;)

Re: 1974 C10 Quadrajet, What Are These Vents?
 

Good stuff Malo!!
Better than I could 'splain it!
So if you get fuel out of them it would mean the discharge port from the pump is plugged. If you're only going 15 miles just remove the pump linkage. It might stumble a bit but won't want to flood either.
There's a tiny roll pin that the arm pivots on, right by that front bolt. Tap it back with a small nail until the arm pops up. THat'll make it ineffective for your short drive.

Re: 1974 C10 Quadrajet, What Are These Vents?
 

Skip the carb shop Caddy! Just do whatever Geezer says. He walked me through Qjet issue a few months back and been running good ever since!!