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Hey guys, I have a 74 small block that is giving me some issues. I recently installed an edelbrock performer intake, new plugs and wires. Initial timing is set to 12° btdc. The car starts and idles great, cruises around the neighborhood just fine too. When I get the car up to about 50mph it starts to surge. Also did it trying to accelerate hard up a hill. My first though was that it could be a fuel issue (Filter was recently replaced). Taking a look at the carb, I noticed the arm that keeps the secondaries from opening wasn't completely moving away
The divorced choke is working and the arm it is attached to can't move any further open. Could this be my problem or does some other device in the carb(Qjet)move the stop the rest of the way?
Last edited by Lamouree351; Jul 20, 2019 at 11:11 AM.
The plastic diaphragm and the rod attached to it prevents the top air valve from opening too quickly.
Is the choke fully opening? there is a lockout on the top that prevents the air valve from opening if the choke is not fully open.
The secondaries do not open at 50 mph.
Are you sure you dont have a vacuum leak between the new intake and the heads or between the carburetor and the intake?
The plastic diaphragm and the rod attached to it prevents the top air valve from opening too quickly.
Is the choke fully opening? there is a lockout on the top that prevents the air valve from opening if the choke is not fully open.
The secondaries do not open at 50 mph.
Are you sure you dont have a vacuum leak between the new intake and the heads or between the carburetor and the intake?
The choke is fully opening. The arm I am referring to is the stop for the lower blades in the secondaries.
I used new gaskets and RTV between the heads and intake as well as a new carb gasket. All bolts were torqued to spec. So I'm fairly confident everything is sealed up.
Last edited by Lamouree351; Jul 20, 2019 at 12:21 PM.
I see what you are referring to but the secondaries are not open at a constant cruise speed of 50 mph.
The secondary throttle blade on the bottom of the carburetor is mechanical so with the engine off and opening the throttle by hand do you see the secondary throttle blades fully opening.
Did you change the position of any of the vacuum lines to the carburetor or intake when you changed the intake. For instance where is the vacuum line going to the distributor connected now versus where it was on the old manifold?
The vacuum lines are all in the same location as before. With the exception of the EGR which is no longer on the car, that port is plugged. The vacuum advance line is the hose shown in the picture. I did a quick vacuum test and I am getting ~17.5" of vacuum at the manifold which is what I had before the manifold swap.
With that arm in the position shown in the above picture the lower secondary blades will not open if I move it to full throttle
Last edited by Lamouree351; Jul 20, 2019 at 05:25 PM.
Why would changing intake manifolds require this to be filed down?
because changing intakes you also changed the choke. both your pic and the youtube video, the choke rod seems to hit the sheet metal housing covering the choke heat coil.
if you disconnect the rod coming from the choke coil at the carburetor end and hold the choke blade wide open while opening the throttle wide open do you have the necessary clearance?
if you disconnect the rod coming from the choke coil at the carburetor end and hold the choke blade wide open while opening the throttle wide open do you have the necessary clearance?
I think your right the lock out lever is being held by the choke. look close at the photo and video, the top of the lock out lever is not where it should be to allow the clearance for the pin. Good catch derekderek and MelWff.
Last edited by Gunfighter13; Jul 21, 2019 at 08:48 PM.
I disconnected the choke rod and moved the choke by hand to the open position. The lockout bar did not move at all... it seems to be just hanging there loose. I'm getting my hands on another Qjet in a couple days to compare against....
I got my hands on a "new" carb. The choke linkage on my carb is definitely not operating in the same manner as the new carb. I decided to put the new carb on the car and take it for a ride. The surging problem was completely gone. I could not see any obvious differences between the two linkage mechanisms. I will have to dig a little deeper to see if I can figure out what is wrong with my carb.
Engine surging under load
