High & Low Altitude
- Ensure engine is at normal operating temperature. Check ignition timing at idle. Disconnect hose from distributor sub-diaphragm, and plug hose end. Recheck ignition timing. Timing should be 5° BTDC. Reconnect hose to sub-diaphragm. Verify that timing advances to about 13° BTDC.
- Disconnect vacuum hose from check valve at Black side and plug hose end. Check that ignition timing remains stationary for more than 1 minute. If timing changes, replace check valve. Stop engine and reconnect hoses to proper location.
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- Disconnect 2 hoses on top of HAC valve. Blow air into each hose and check that air flows into carburetor. Reconnect hoses to proper locations.