A vacuum leak can go away when the engine metal gets hot and expands.When cold your choke valve is closed and the vacuum is pulling in extra fuel. Check around the intake manifold, carburetor base and any vacuum lines attached. So your engine seems to crap out once the engine gets warmed up.Ī vacuum leak can cause this. Only Runs With Choke Valve Partially Closed Did you match your carburetor number and is the carburetor number tag on the correct carburetor? If the carburetor number doesn’t find the correct pump then find a pump shorter than what you have and try again. Most likely you have the wrong accelerator pump. Also, are the secondary throttles opening and closing completely? Or is there some sort of interference, including from an incorrect base gasket? The Accelerator pump cup gets stuck at the bottom of the well and comes off the pump stem. which could be downstream of the carburetors. My first instinct is that he has a vacuum leak.

Ive set the pump and metering rods per your specs and cant make it any better. It accelerates good if you push the pedal down but if you try to hold the rpms at like 3000 it swings up and down. One of them starts and idles good but when you try to raise the rpms it swings frm 1000 to 3000 rpms. I soaked and cleaned my 2 carb both the 1 inch for a chev. (sometimes it helps to dampen the paper towel a bit) The bigger orifice jet goes in the primary side.Ī piece of paper towel folded over the screwdriver blade will hold the part, or a screw, until it gets started in the hole. Using Ethanol Defense will help eliminate your ethanol problems. Now when you press the accelerator pump to the bottom fuel should squirt out of the venturi cluster holes. Run thin wire through all of the passages in the venturi cluster and then replace it. Replace the main discharge ball, spring and T. Don’t hit too hard, or the check ball might get stuck. If you get fuel out of the main discharge while holding down the check ball, then use a brass drift punch to gently tap on the check ball. You should now get some resistance when pushing the accelerator pump down. Replace the main discharge check ball and using a brass drift punch, hold the check ball down so that the hole seals. If fuel comes out of the main discharge, then the check ball and passage way is probably ok. The pump well check ball should seal the intake hole and fuel will be forced out to the main discharge.

Fill the pump well, then press the accelerator pump down to the bottom.

Take the venturi off, remove the main discharge T, spring and check ball (bigger check ball). Ethanol will leave residue behind that cleaners cannot get out. If the well doesn’t fill up, then the passage is probably plugged up. In other words it splashes over from the float bowl. For those that don’t use a check ball, the well if filled by coming over the slot in the side of the pump well. The check ball will lift up by the weight of the gas and allow fuel to flow into the well. Test the check ball by taking the top off. The check ball that resides here will be the smaller check ball and it is often aluminum. The other will be on the bottom and that would be the intake. One will be slightly up the side near the bottom and that is the discharge hole. The way to tell is to look for two holes. Make sure that the check ball is in the bottom of the pump well, if your carburetor needs one. There is where I would concentrate your efforts. When you step on the gas an extra squirt of gas is needed and that is provided by the accelerator pump circuit. Don’t forget that the distributor advance not working correctly can cause a similar problem. I will assume your electrical system is ok. The carb seems to be adjusted properly and the timing is correct for the engine. I ran it for a couple of days and this “dead spot” showed up. Once we got the float fixed it seemed fine. The carb is newly rebuilt and is very clean. My brother says it might be the accelerator pump. You can even floor it after you are moving some and it seems okay. If you are at a stop and punch it, the car dies but if you accelerate gradually it is fine. If you punch it, the car will sometimes die or it will almost die then rush back to life. If you accelerate slowly, the car is fine. The carb seems to have a “dead spot” I was hoping you might have some suggestions.

Carburetor troubleshooting guide