The Stovebolt Site Forums The Shop Area Engine Shop Two questions- ventilation and lowspeed stall

My 1970 350 has a Rochester 4gc. I don't see a vacuum port for crankcase ventilation. There is a plugged port on the back of the carb at the base--is this for PCV? The engine has chrome dress-up valve covers with vented oil filler caps,but no PCV fitting, plus the tall oil fill tube by the thermostat housing. The firewall is covered in dirty, oily grime. Is it appropriate to replace one of the filler caps with a PCV fitting and pipe it to the port at the back of the carb? I would think an engine of this vintage would have had PCV from the factory. Second, when slowing down fairly rapidly at a stop sign or in a parking lot, the engine will often stall. It starts right back up, and I cannot duplicate this problem in the shop. It definitely seems like a carburetor problem, but what component is at fault---needle valve, floats, jets, metering rods ???

By 1970, I believe all the Chevy engines had Quadrajet carbs, so you've got an earlier-model intake on yours. If the port at the back of the carb is 1/4" pipe thread or larger, you can put in a 1/4 NPT to 3/8" tubing fitting and run the PCV hose to it, which just happens to be 3/8" inside diameter- - - -handy, huh? I'd suggest putting a PCV grommet into the passenger's side valve cover in place of one of the filler caps, but be sure there's a baffle inside the valve cover to prevent the PCV valve from sucking in liquid oil.

Does the 4GC have a "dashpot" installed on the throttle linkage? It's a spring-loaded throttle stop that returns the linkage to idle gradually, rather than letting it close suddenly. Every 4GC I've ever worked on has one, and some of them have a vacuum connection to assist in the throttle-closing process. If the vacuum is low, like after a sudden acceleration, the dashpot drops the throttle linkage back slower, to prevent the stall you're describing. Other dashpots simply have a spring and a diaphragm, which acts like a shock absorber for the throttle linkage.
Jerry

There is no dashpot on the carb linkage. This engine and all its components are as I bought it 10 yrs ago. I know it to be a 1970 truck engine by researching casting numbers, but otherwise am ignorant of what has been added or modified. I just checked another 4gc core I have, and it does not have a dashpot either, but it does have a PCV valve in that port in the back--1/4" NPT. I may do a quick retro-fit. If these 2 carbs do not have dashpots, what's the next alternative? Would I be smart to buy a new Edelbrock squarebore?

Dashpots should still be available, possibly through professional-level suppliers such as NAPA, not from the mouth-breather computer jockeys at Auto Zone, etc. A good-condition 4GC is a far better carburetor than either Holley or Edelbrock, etc. aftermarket carbs. However, I don't recall any 4GC's that were calibrated for a 350 engine. If you are determined to make a change, find a year-correct intake manifold and a proper part number QuadraJet. Our resident carburetor guru "Carbking" might be able to help you procure a dashpot that will cure your stalling problems. He runs a very professional rebuild shop, but Carter carbs are his primary specialty.


Edit: This one is probably what you need, but there were lots of slight variations:

http://cgi.ebay.com/ebaymotors/D5-2...arts_Accessories&hash=item3a3f9360db

Jerry