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 Jim Grant's Tech Tips '85 Chevrolet Caprice Classic, Carburetor Leak Down
Q: I have a really wonderful and unreplaceable ’85 Chevrolet Caprice Classic Station Wagon. It is approaching the 250k mileage mark and runs perfectly except for one eccentricity, which given the age and history of good performance it is entitled to. If the vehicle is driven (and therefore started every day) it starts immediately. However, if it is left to set for more than a day there is a problem. Evidently the fuel somehow leaves the carburetor. The longer it sits, the drier the carburetor becomes. There is a simple remedy, just poor some fuel directly into the carburetor and it will start right up. When this first happened, I assumed that the little pump that primes the carburetor when the accelerator is pushed to the floor was worn out, and I had the carburetor rebuilt. That accomplished nothing. Next I replaced the fuel pump, believing that the back flow was not working-no dice. My mechanic is now suggesting that the carburetor has become porous and the fuel is draining out (although I never smell gas) and that I should replace the carburetor. But, with the vehicle, being so old, this is not a simple matter. Apparently, they made a myriad of carburetors for this engine. Any thoughts? A: There were porosity problems with GM carburetors, allowing them to leak fuel without it ever being seen. The fuel would leak into a vacuum passage and into the intake manifold. The most common problem was due to the metering well plugs leaking fuel. In some cases it was so bad that the carburetors would be dry the next morning if the vehicle set over night. If the metering well plugs are leaking, they can be epoxied to seal the leak. The same can be done to the base of the fuel bowl itself if that is the cause. The trick is finding a technician that is familiar with your carburetor. It has been many years since carburetor rebuilding was taught in the tech schools or at training clinics. You’ll be looking for an old school technician who is still spinning wrenches. I would not suggest having a rebuilt carburetor installed. Why? The carburetor on your vehicle was designed for that engine and vehicle chassis. A rebuilt carburetor will fit, but it can be from a variety of GM vehicles; it just may not perform the same. If you check on the internet, you’ll likely find some companies that specialize in rebuilding carburetors. If you can tie your vehicle up for a week or so you can have the carburetor removed and sent out for rebuilding and sealing. A couple of side notes; the fuel filter for your vehicle’s carburetor should have a check valve in it to prevent fuel from draining back/out of the carburetor. In addition, an electric fuel pump can be installed to prime the fuel system and refill the fuel bowl of the carburetor.
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