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Comments on the Holly 4000 Carburetor
Walt,
My '55 hesitates, when warmed up, when I take off from a stop or when the car is moving and I release the accelerator and then go to accelerate. At times the engine dies out until I back off the accelerator and accelerate slowly. I have replaced the vacuum advance unit (which was bad) and overhauled the "tea pot" carburetor, including a new accelerator pump. Any ideas would be greatly appreciated.
George (not George Lang!)
George,
Overhauling the Holly 4000 Is not going to do the trick, you have to FIX IT. Forgive me if this sounds arrogant but I have worked behind so many, many carburetor overhauls which weren't successful, I must be blunt in order to make my point. Before one can properly repair a carburetor he must understand what every little passage way, every little check ball, and what every other part of the carburetor does, how it does it and why. Just taking a carb apart, cleaning it and reassembling it with a handful of new parts seldom gets the job done. I am almost certain your hesitation problem is caused by carburetor malfunction. I want to help you fix it.
Let me give you one example of a mistake I often find when repairing Holly 4000'5. The gasket between the secondary diaphragm assembly and the throttle body can be installed 6 different ways and I have found them on high dollar overhauls all 6 different ways. Needless for me to say only one way out of six is correct. If it is not positioned properly the secondary throttles never open. This is not a Chevy mechanic-proof carburetor. That is why many people think they are no good. In reality they are very good carbs when they work right.
I recommend that every one who wants to learn more about the Holly 4000's obtain the Holly service manuals # C-228 for a '55 or a # C-228-1 for a '56 from CTCI. All following references are to the '55 Holly service manual # C-228.
George, from your description it sounds as though your carb has very poor or no transition from idle to venturi boost. Poor transition is usually caused by an ineffective accelerator pump. Some of the causes are the inlet check ball and it's retainer shown on page 17, figure 13. Does the ball seat properly? Is the pump discharge needle valve # 25 on page 15 in place and does it seat? Is the float level high enough? It should be 114" below the top edge of the fuel bowl. If set too low the carb will have poor transition. Pump performance should always be liquid checked during the assembly of the carb. Liquid checking prevents many problems later.
Another cause of poor transition is an idle mixture that is set too lean. This is most often caused by air from the atmosphere leaking into the idle passageway at the point where the fuel bowl foot attaches to the throttle body. Proper assembly at this point is critical. The protruding foot of the fuel bowl is often so severely warped it will not seal. This must be fixed; it can be straightened. A special gasket can also be improvised. Whatever can be done, must be done. None of the three passages should be permitted to leak at this point. Proper testing at this time is absolutely critical. I use a "Mity-Vac" to test it. Have a look at the "Mity-Vac" by visiting their site at http://mityvac.com/index.html. You will find many uses for this tool once it is in your toolbox. I find it essential in the repair of Holly 4000 carburetors.
Walt Nuckels CTCI #861
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