Many times when rebuilding our old cars, we carefully rebuild the engine and drive train, and have the doors closing with vault-like precision, but will leave one or two little things that annoy us and, ultimately, keep us from driving the car. It might be a body squeak, no brake lights, or, in the case of our '49 Buick Roadmaster Sedanet, a faulty operating choke valve.
The Buick's complete drive train and mechanics have been rebuilt, the car has been painted, and all that's left now is the interior and putting the chrome back on. It is time to address the choke problem before drive time. The problem with the choke is that it doesn't get enough heat from the manifold to the choke to fully open. On a 12-volt car, you could put on an electric choke, but there aren't any 6-volt chokes. You could specially wire a 12-volt to work, but I would rather make the original work. If it's set almost closed at starting, it starts easily, but doesn't open fully, running rich and fouling out plugs. The carburetor has been rebuilt and the thermostatic spring replaced with a fast-opening one, called a rebuilder's spring, available from Daytona Parts, 386-427-7108.
When we were rebuilding the engine, we removed the exhaust and intake manifolds, resurfacing them and checking the condition of the heat source or inner tube. This is the tube that goes through the exhaust manifold, into which the choke pipe is inserted, which goes back to the choke housing of the carburetor. It is crucial for this pipe to be in good condition, with no holes, breaks or clogs, providing clean air to the choke. If you have ever seen a choke housing that is gummed up with soot, it is caused by a bad heat source pipe. Checking the condition of the pipe with it still on the car is easy. First, find each end of the pipe on the manifold. The top end of course has the choke-to-carburetor pipe in it, and the bottom is directly opposed on the bottom side of the manifold. Remove the choke-to-carburetor pipe and use compressed air with a nozzle to blow through the top hole, putting your finger on the bottom hole of the tube. If you do feel pressure on your finger and don't hear any air hissing inside the manifold, the tube is clear and good. If you don't feel pressure and don't hear air, the tube is stopped up. If you don't feel pressure and do hear air inside the manifold, the tube is broken inside or has holes in it, and must be replaced with a steel line that can withstand the exhaust manifold's high temperature.
Once the manifold pipe is working, the next step is to make a choke pipe. These pipes are generally made out of one of the following metals: 1. Steel, 2. Aluminum 3. Copper. Most choke pipes from the factory were steel. Aluminum replacement tubes generally come in today's choke kits. They also include a compression fitting, compression nut, sleeve insulation and a pipe-to-manifold adapter if it is necessary to step the 1/4" pipe down or up to the manifolds inner tube. These kits work well most of the time, but the compression fittings don't work with all carburetors. Strombergs of the '40's, as the one on our Buick, has a thermostatic spring cover that requires a flared fitting which allows the pipe to pull up tight (but not too tight) to the spring plate. With a compression fitting, the fitting itself takes up room inside the nut, only allowing the nut to lock down on 2-3 threads.
When making the choke pipe, the metal it's made of can make a difference in how much heat gets to the choke. Metals are rated in thermal conductivity @ 300 degrees Kelvin (room temperature), in watts/meter--degree Kelvin. Of the three metals discussed here, copper has the best conductivity, or CU= 401 W/MK. Next is aluminum, AL=237 W/MK, then carbon steel at 35 W/MK. Simply put, copper conducts more heat! So, I chose 1/4" flexible copper tubing to make the choke pipe for the '49. Using the old pipe as a guide, I cut a piece of copper tubing to the correct length, laying it alongside the old piece to mark the bends on the new tube with a Sharpie. I test-fitted the nut to make sure the 90-degree bend at the choke would allow the nut to go on and have enough room to flare. A good, full flare is necessary, or the pipe will ratchet around inside the nut when it is tightened down. Using the wedge tool on my tubing cutter, I reamed open the manifold end of the newly-cut tubing, opening out the end that the tubing cutter had closed down, to provide better air flow. With that done, I test-fitted it to the car. It fit great and I was now ready for the high-temp sleeve insulation. Quarter-inch insulation sleeve is nearly impossible to find, but I did find some 3/8" that worked out well, allowing plenty of room for bends and providing enough clearance to slip it over the end of the nut for a good seal. I found this in a 50-foot spool of fiberglass insulation for $41. It can take continuous 1200-degree heat (very important!) and melts at 2048 degrees, available in silver or black. It holds its shape nicely and looks right on the car. I got it from Cable Organizer, manufacturer's part number FGNO.38, at 800-222-0030. When cutting the sleeve, use a hot knife, which keeps the threads from unraveling. After sliding on the insulation, I installed the pipe, set the choke, and fired the old Buick up! It started quick, ran smoothly during warm up, and the choke opened all the way when it reached operating temperature.
I think old cars are a little like us: Sometimes they need a little extra tweaking to make 'em run right! Next month we'll cover setting the choke. See you then, and keep 'em driving!