Preliminary Tuning of a New
Racing Carburetor

All C&S custom carburetors are factory set to the usual settings for the intended application.

The following tuning information will not be needed if the standard settings are correct for the customer's motor.

The idle and throttle response adjustment of the C&S product is much greater than a stock carb.

Install carb on motor and bring engine up to operating temperature (at least 180 degrees F).

Check fuel level in float bowl. Float level is preset at factory, but will be affected by fuel pressure of customers motor. Correct setting with motor running is fuel should barely run out of sight plug hole on side of float bowl. To adjust, loosen slotted screw slightly on top of float bowl, then turn nut clockwise to lower level and of course, counter clockwise to raise level. One flat on nut (1/6 turn) will raise or lower fuel level 1/32 of an inch so less than one full turn will bring fuel to proper level. A shop towel around nut will catch any fuel that squirts out.

Donít skip this adjustment. Fuel level affects main circuit startup and has a small effect on wide open throttle air/fuel ratio. On rare occasions a slightly higher or lower setting will solve problems. But, unless you are an expert tuner, stick with the standard setting. It will almost always result in greater performance.

You are now ready to tune idle/transition settings.

All C&S carbs start with throttle position as shown in sketch ďAĒ. The front throttle butterflies are never changed from this position. Disregard anything you may have heard to the contrary.

Adjust idle screws on side of metering blocks one by one (most have 4 screws, some only 2). They are very sensitive. Adjust to get the highest possible idle RPM even if this results in a higher RPM than you want. If RPM is too high, shut off engine, then open carburetor wide open. This will expose a small headless allen stop screw on the right side of the rear throttle linkage, see photo.

While holding the throttle wide open turn screw in (clockwise) about 1/6 turn to reduce RPM about 200 RPM. And of course, turn screw out to increase RPM. Stop screw has a nylon patch to keep it where it is set.

Then go through the process again until the desired RPM is reached.

You will not only have the best mixture at that RPM, but it can be readjusted if major conditions change or carb is installed on a different motor.

Take time to do this right! Proper adjustment is critical to sharp throttle response.