Basic carburetion and ignition timing – the keys to classic musclecar power and performance.

It’s unfortunately a lost art in these days of electric computer controlled tuning. But the simple fact is, setting the proper engine timing and tuning your carburetion are key to making your musclecar run correctly. Certainly you can invest the money to install fuel injection on your upgraded musclecar, but for many, a simple carburetor and mechanical advance distributor is required to retain the vehicle authenticity. Even for those of you desiring more sophisticated ignitions will find that mechanical advance distributors, despite some of their inherent simplicity, can still get you a trip to the winner’s circle.

Timing

The basic timing setup for most musclecars is a certain amount of advance timing to provide proper combustion in the cylinders followed by a little distributor advance timing to help get you down the road. Some of the timing is set initially at the crankshaft (that’s why you still have a timing light) and the other advance is added to the engine as the rpm rises. Classic musclecar distributors commonly use spring loaded weights in the distributor that spread apart (through centrifugal force) as the rpm increases. For most musclecars full advance comes in by about 3000rpm. To deliver different amounts of advance a variety of weights and springs can be added to the distributor.

Bob and Nick Jennings have been tuning engines for years. Frankly, they can tune a distributor in their sleep (and often do) a talent that comes from years of practice. For our 383cid Mopar engine, the initial timing was set at 16 degrees. In the distributor they installed an additional 20 degrees of advance. In our case the total of 36 degree of advance comes through the adding of the initial and distributor advance figures. Original factory settings are more in the range of 28 degree advance in the distributor and only 6 to 8 degrees initial timing which makes for sluggish bottom end performance and economy.

To test our new timing settings, we ran the car on the dyno taking careful note of any detonation (knocking). If the engine detonated, the timing would be backed off (reduction of the initial advance timing) and tested again. Just like the old days, often the final timing of the engine was based on the drivability, quality of the fuel, altitude, carb-jetting and a multitude of other factors. As most musclecars run around 10:1 compression, only premium fuel should be used.

Carburetion

Most performance musclecars used some form of Holley four-barrel carburetor. That is a good choice for fuel metering as they are easy to work on and highly tunable. Most classic performance musclecars require a full rebuild which means taking them apart, coloring them back to factory looks and the assembling then repairing many of the common Holley weaknesses that can cause poor performance. Most commonly a Jennings full service rebuild includes removing the boosters as well, increasing fuel flow and truing up (sanding flat) the metering plate surfaces, which can warp with time. The whole process takes only a few minutes – if you have the ready parts at hand. Rebuild kits are available for any of these carburetors but certain tools such as the one used to remove and reinstall the boosters can be costly if you are only rebuilding one carburetor. Services, such as Jennings are available in many locations so check out your local service before investing in this one operation.

Follow along as we take you through the basics of engine timing and carburetion upgrades. They are two areas that often make the difference between getting what you paid for when you envisioned your vehicle’s performance and missing the boat.

For the first time builder, a carb-rebuilding manual is a good idea. These carburetors take little more than a few simple hand tools to take apart and rebuild kits are plentiful.

Codes stamped in the air horn tell volumes about the originality of the carburetor. From here it is easy to determine the original application and the rebuild kit required to restore it to original performance configuration.

Holley carburetor throttle blades and shafts are a common problem area. They can improperly seal the throttle openings affecting idle and acceleration characteristics. Inspecting these parts is a good first step to determine which new parts may be required.

Over the years, Holley floats have come in various styles and materials. This older style tin float was common in the ’60s. Make certain the floats are not damaged and replace the needle and seat before reassembling your carburetor.

Holley carburetor designs have changed over the years. While external metering blocks are the most common for original musclecars, internal metering blocks that were housed within the fuel bowl were a design upgrade. To remove these metering blocks, a special clutch head screwdriver is required.

Linkages are made from differing metals and can rust if the “right” conditions exist. Carburetor cleaner will remove much of the sludge and grime but not rust. These parts should be replaced to avoid any potential for throttle binding.

The basic Holley carburetor bodies were a greenish color that can become brown over the years. Holley offers a complete reconditioning process for those looking to regain the original look as can full service shops such as Bob Jennings Dyno Service.

Most musclecars used distributors featuring mechanical advance weights to add timing as engine rpm increased.

On this distributor, the center reluctor was carefully slid off of the distributor shaft making sure not to damage any of the external fins.

The rotor head was removed from the distributor shaft after the C-clip holding it in place was taken from the center of the shaft.

The mechanical advance weights in the distributor are marked as to their weight and have a dramatic effect on the advance curve (amount of timing induced) into the engine. Ask an expert to give you guidance on the proper weights for your application.

While the weights used in the distributor are one advance curve adjustment, the weight springs also have an effect in speeding up or slowing the speed with which the advance is given. Most springs are color coded to help determine the precise rpm of the full advance cycle.