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 adjusting slot in throttle control valve lever with a screwdriver. See Fig 1 . If speed was too high, narrow slot with pliers.
- If speed cannot be adjusted, or diaphragm will not hold vacuum, replace throttle controller and retest.
- If speed was okay, disconnect vacuum pump and reconnect hose. Raise engine speed to 3500 RPM and maintain for 2 to 3 seconds.
- Release throttle suddenly and note length of time throttle opener arm takes to fully extend. Return time should be 1-4 seconds. If engine speed returns to idle in 1-4 seconds with arm fully extended, system is okay.
- If return takes more than 4 seconds, check throttle controller linkage for free movement, replace dashpot check valve and retest. If return takes less than 1 second, disconnect hose from throttle opener and connect a vacuum gauge to disconnected hose. Start and run 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 carburetor port. If there is no vacuum, clean carburetor port and retest. If vacuum is present, check vacuum line for leaks, blockage or disconnected hoses and retest.