FINDING WHAT AILS AN ORIGINAL 1970 PLYMOUTH GTX
Finding what ails an original 1970 Plymouth GTX
Diamonds in the rough still happen. Lost muscle cars are discovered in barns across the country every day. Most are good cars gone bad, forgotten until someone realizes their value. Regardless of where you find them, figuring out how to get them back on the road takes attention to the basic elements of engine operation. With great regularity, these cars often have similar issues that cause them not to run due to some simple rules that any novice mechanic can address.
If there’s one motto any mechanic will recite, it’s the three rules of proper engine operation: fuel, air, spark. Take any one of these elements away and your engine will fail to not only run right, but could cease to operate as well. Stir in the need for a properly timed spark arriving at the point where the fuel and air car be ignited and you have the most common malady that causes frustration with vehicle projects — regardless of whether the car came from a barn recently or not.
Such was the case with this 1970 Plymouth GTX. A pristine example of the breed, this 440-cid–powered original black GTX was running very rough and needed a class in Troubleshooting 101 to get it running right. While the problems found with this car may not be present on yours, it’s a great example of some of the most common things that happen with these classic muscle cars. In addition, we recommend giving your car a thorough safety review. It’s critical if you intend to drive your vehicle, regardless of whether that’s across the country or across the street.
Another important tip for all classic muscle car owners: Buy a factory service manual for your vehicle. These manuals are very helpful not only for basic maintenance, but also for larger projects involving disassembly or repairs on your vehicle. While a lot of this information can be found on the internet, a huge amount of misinformation will only cause you more frustration. These manuals will save you countless hours by showing you the proper way to take things apart. Trust us — they’re well worth the investment and places like Year One and Classic Industries offer reproductions of these original manuals, so you can order one online and have it at your door in a couple of days.
Follow along as we get our GTX back on the road!
We begin our review of the 440-cid engine and an inspection of the Carter AVS carb. This original car showed 96,000 miles on the odometer and was running rough especially upon initial throttle tip-in.
Remove the carb top screws and lift off the top of the carb, making sure not to drop any screws down the carb or into the open intake manifold. Once on the workbench, turn the top upside down to quickly reveal if the float levels were set evenly. Check the floats don’t have any pinhole leaks, causing them to sink once inside fuel bowl. Replacing these floats is a cheap way to ensure this isn’t the case with your carburetor.
The first problem was obvious and dangerous. This battery cable is original equipment, but ran its course, and in need of immediate replacement. Even if your cables look great, remove them and clean the battery posts with baking soda (make sure to wear skin and eye protection), brushing the terminals and cable eyelets with a wire brush, and retighten to make certain they deliver full power to your engine. Make sure all ground cables (negative) are properly installed and none are removed.
The 440-cid engine was completely stock right down to the original-style plug wires, which can be a common weak link in the ignition chain. Each plug wire was inspected for breaks in the insulation, and we ultimately just changed out the entire wiring system to be safe. Each of the spark plugs were taken out, the carbon removed with a media blaster, cleaned with solvent, and then reinserted after re-gapping of the electrode.
The accelerator pump linkage is removed in this manner. The accelerator pump was considered the prime suspect in the acceleration problem, since clearly the car had been sitting for some time.
Before removing the top of the carb, the rear bracket and fuel line need to be removed. Double check the carburetor is correctly tightened to the intake manifold and the intake manifold to the cylinder heads.
Since the engine was exhibiting a stumble off idle, we started with the carburetor. First, the metering rods were removed after removing the screw caps that cover them from the top of the carb. They should be removed and cleaned before taking the top off the carb. Make sure to note from which side of the carburetor each of the metering rods were originally located.