Figure 4-4. Checking ignition timing.

Figure 4-4. Checking ignition timing.

4-24. Manifold Vacuum Test

manifold. Elbow is located directly above exhaust

manifold heat control valve.

a. General. Performance of the manifold vacuum

(2) Install vacuum gage hose adapter in hole.

test will provide an indication of sticky valves,

and connect vacuum gage hose to adapter (fig. 4-5).

leaking head gasket, fouled spark plugs, carburetor

(3) With engine warm and idling at 450 to 500

a d j u s t m e n t , timing adjustment and mechanical

rpm, vacuum gage reading should be between 18

drag.

and 20 inches of mercury, and steady. Refer to

b. Procedure.

figure 4-5 for normal and abnormal indications.

(1) Remove PCV valve elbow from intake

4-8