Hi guys, a little help please. My brother just put a remaned correct year Q-jet on his 1973 Corvette 350. The 350 is freshly rebuilt with a little extra cam. It is a 4speed, when you put it in gear and punch it, it boggs down and refuses to actually let the secondaries to open. What could be common cause?
Take a look at the secondary air valves. With the engine off, push them in with your finger. On the secondary air valve shaft is a small plastic cam. As the secondary air valves rotate open, the cam should lift the secondary rods via the hanger. If the cam is broken, the rods will not rise out of the secondary jets. You'll have a huge bog because the carb will go very lean. Make sure you can not push the air valves in WITH THE ENGINE RUNNING. If you can, check the front vacuum break on the passenger side of the carb. Engine vacuum should pull the link in and hold the airvalves closed. Make sure the accelerator pump is functional. With the engine off, open the throttle briskly and look for 2 streams of fuel in the primary barrells. And finally, make sure there is no vacuum leak.
Also make sure the choke is fully disengaged. If it is not it can keep the secondaries from opening. This should not cause a bog though, just have no power.
These carbs are notorious for sticking power pistons, especially if the rebuild is incorrectly done. It is very easy to create a problem for the power piston to be held in place by the air horn gasket if it is improperly installed. Try this: With the engine off, remove the air cleaner and using a small long screw driver, try to push the power piston down. It should easily and smoothly move down, then spring back up. If it does not, the air horn woill likely have to be removed to find out why. Ray
Just as a foot note, to do the test Ray is talking about you need a thin screwdriver inserted down the vent tube. It needs to be angled toward the front of the carb. The very edge of the power piston extends just into the front edge of the vent. If you put the screwdriver in straight down you will just be hitting gasket. Takes a little maneuvering the screwdriver around to find it, until you get used to doing it.
