I recently had a local garage replace my Quadrajet a new Holley 4175 carburetor on my 1972 stock (350 ci, 4 speed) corvette. The car always starts right up when its cold and runs great- probably the best that the car has ever run. But I'm having trouble with it starting when it's been warmed up and it sits for a short period of time (say an hour or two). Let me be more specific- the car starts right up but after several seconds of running it cuts out. Then I practically have to flood the engine to get it to start again-kinda kills the cool factor when you struggle to start your classic Vette. I am not very knowledgeable when it comes to carburetors so please make any explanations or suggestions pretty simple. I've taken it back to the shop a couple of times but it keeps coming back with the same problem. Thanks in advance for any advice.

Joe

 

Go to a different shop, those guys don't know what there doing it might not be a carb issue at all could be vacuum leak. If it had no warm start issue with the q jet then it is something they did replacing it or tuning it, or it some other issue making the carb seem faulty. Why did you replace the q jet?

 

It will usually be one of two problems: 1)choke is maladjusted and the choke is closing when the engine is hot causing a flooding condition. You can observe this yourself by removing the air cleaner cover before you start the car, open the throttle and see if the choke blade moves to the closed position. The choke blade will never be fully closed even when cold but if the engine is hot, the blade should move only slightly depending upon how long it has been sitting. After a couple of hours, it will probably close nearly half-way. If the choke is badly adjusted, the solution to this is to lengthen the rod from the choke spring to the choke mechanism, or; 2)most likely your carburetor is percolating fuel into the intake manifold when it goes into heat soak. You can overcome this by instead of pumping the throttle when you attempt to start it by just putting the thottle on the floor and holding it there while you attempt to start it. It's a bit harder to diagnose fuel percolation but the throttle on the floor while cranking gives you a substantial clue that it is happening. You can take off the air cleaner open the throttle, then manually open the secondary and using a flash light look for puddled fuel on the intake plenum floor. The fuel percolates when the carburetor absorbes too much heat from the intake manifold. This is usually the result of using a thin fiber gasket and not using a thicker insulator gasket.

 

I go along with thiatt!! I replaced my q jet with the 4175 also. Make sure all vacuum lines are hooked up correctly and that the electric choke is connected correctly. I used the yellow wire to the wiper for power. I have no problems. 71 350/270...
Mike

 

There are two idel scerws one on the choke that controls idel when choke is on or the engine is cold, it is on the choke side. Other is idel scerw on the other side easy to see if your vette runs when it cold it is ideling on the choke idsel scerw, then when it warms up and the choke is open it goes to the other idel scerw, check the idel when it is warm. I had the same problem but mine would not idel down when warm the idel scerw was holding it open