Dashpot System Check
- Connect tachometer to engine. Warm engine to normal operating temperature (cooling fan on). Disconnect vacuum hose from throttle control valve.
- Connect hand vacuum pump to throttle control valve and apply 8 in. Hg vacuum. Check that engine speed rises (within 1 minute) to 1500-2500 RPM.
- If speed was too low, widen the adjusting slot in the throttle control valve lever with a screwdriver. See Fig 1 . If speed was too high, narrow the slot with pliers.
- If speed cannot be adjusted, or diaphragm will not hold vacuum, replace the throttle control valve and retest.
- If speed was okay, disconnect the vacuum pump and reconnect the hose. Raise the engine speed to 3500 RPM and maintain for 2 to 3 seconds.
- Release the throttle suddenly and note length of time the throttle opener arm takes to fully extend. Return time should be 1-4 seconds. If the engine speed returns to idle in 1-4 seconds with the arm fully extended, system is okay.
- If return takes more than 4 seconds, check the throttle controller linkage for free movement, replace the dashpot check valve and retest. If return takes less than 1 second, disconnect the hose from the throttle opener and connect a vacuum gauge to the disconnected hose. Start and run the engine at 4000 RPM.
- Vacuum should be at least 1.2 in. Hg. If so, replace dashpot check valve and retest. If vacuum is less than 1.2 in. Hg, check for vacuum at the carburetor port. If there is no vacuum, clean the carburetor port and retest. If vacuum is present, check the vacuum line for leaks, blockage or disconnected hoses and retest.