| Problems | Carburetor doesn't adjust properly | Carburetor floods | Fuel leaks at shaft | Internal fuel leak | Misses or surges | Stumbles or loads up | Engine won't idle | Rough idle | Backfires | Bogs | Hard starting | Lack of power | Pinging at moderate cruise just off idle | Engine stalls on hard braking | Low fuel economy |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Possible Solutions | . | . | . | . | . | . | . | . | . | . | . | . | . | . | . |
| Check for air leaks. Make sure carburetor and manifold gaskets seal properly. All outlets must be plugged or connected. | X | . | . | . | X | . | X | X | X | X | . | X | X | . | X |
| Check ignition system. Replace parts as necessary. Adjust timing to proper specifications. | X | . | . | . | X | . | X | X | X | . | X | . | X | . | X |
| Check choke adjustment. | . | . | . | . | X | X | X | X | X | . | . | X | . | . | X |
| Change carburetor fuel filter and/or in-line fuel filter. | . | X | . | . | . | X | . | . | . | . | X | X | X | . | . |
| Too lean. | . | . | . | . | X | . | . | . | . | X | . | X | X | . | . |
| Check float level and drop. | . | X | X | . | . | X | . | . | . | . | . | . | . | X | X |
| Check idle mixture screw adjustment
See below |
X | . | . | . | . | . | X | X | . | . | . | . | . | . | X |
| Too rich. | . | . | . | . | . | X | . | . | . | X | . | . | . | . | X |
| Increase accelerator pump stroke. Pump squirter size change may be needed. | . | . | . | . | . | X | . | . | . | . | . | X | . | . | . |
| Check for dirt or metal in needles and
seats.
Needles and seats may need replacement. See below |
. | X | . | X | . | . | . | . | . | . | . | . | . | . | X |
| Check for dirt blocking the low speed
circuit. Clean unit and apply air pressure. Install in-line fuel filter.
See below. |
X | . | . | . | . | . | X | . | . | . | . | . | X | . | X |
| Check floats for leakage. Replace if necessary. | . | X | . | X | . | . | . | . | . | . | . | . | . | X | X |
| Check air horn gasket. Replace if deterioration or breakage is present. | . | X | . | X | . | . | . | . | . | . | . | . | . | X | X |
| Fuel is boiling due to excessive under hood temperature. See below. | . | . | X | . | . | . | . | . | . | . | X | . | . | . | X |
| Fuel pressure too high. Fuel regulator
may be needed.
See below. |
. | X | . | X | . | . | . | . | . | . | . | . | . | X | X |
| Fuel pressure too low. Check fuel system. | . | . | . | . | X | . | . | . | . | . | . | X | . | . | . |
| Check secondary latching device and rod for proper movement. | . | . | . | . | . | . | . | . | . | . | . | X | . | . | . |
| Lower float level slightly . | . | . | . | . | . | . | . | . | . | . | . | . | . | X | . |
**Dirt/metal shavings between the needle and seat or a "sticking float": To correct either of these problems, lightly tap the carburetor fuel inlet area with the handle of a screwdriver. If flooding continues, pinch the fuel line (if possible). Start the engine and let it run until it stops. Release line and restart engine. If flooding persists examine the needles, seats, float level, and float drop. Adjust or replace parts if necessary.
Excessive under hood temperature: Ensure fuel line is not located too close to heat sources such as the exhaust or block, causing expanding fuel to be forced past the needle and seat. Fuel can also boil inside the carburetor due to missing gaskets, spacers, or heat shields. Also check to see if the exhaust heat riser is stuck, allowing excessive heat under the carburetor.
Excessive fuel pump pressure: Avoid extremes in fuel pressure. At IDLE, there should not be any more than 6.0 psi; if the vehicle has an adjustable fuel-pressure regulator, set it to 5.5 psi. With most fuel pumps the minimum fuel pressure is encountered at high rpm and WOT. Fuel pressure should not drop below 2.0 psi. If it does, a fuel pump with more capacity may be required.
ConventionalIdle Mixture Screws that provide a leaner A/F when turned clockwise and richer A/F when turned counter clockwise. The idle air flow is controlled by a conventional screw that opens the Primary Throttles. The following procedure should be used to set the idle mixture and speeds.
1. Fully warm engine and ensure choke is fully open.
2. Air cleaner in place.
3. Set desired speed with the air screw.
4. Adjust the Idle Mixture Screws on ONE side to get the maximum possible RPM. Do not go rich beyond the maximum speed point.
5. If the above changed the idle speed more than 40 RPM, then readjust the speed.
6. Adjust the side OPPOSITE of that in Step 4 to get maximum RPM.
7. Reset the speed.
8. Carefully trim each Idle Mixture Screws to again get the maximum idle RPM.
9. Go leaner just enough to get a 20 RPM drop in speed.
10. Reset the speed to the desired RPM.
11. This is a Lean-Best Idle Set. Setting richer than this will not improve idle quality or performance, but could tend to foul plugs.