Figure 4-51. Checking Timing with Timing Light

Figure 4-52. Timing Marks

Figure 4-51. Checking Timing with Timing Light

j. Remove the timing light and connect the

c. Connect plug wire to spark plug adapter.

vacuum line.

d. Clamp timing light spark plug lead to the spark

4-51. INTAKE MANIFOLD VACUUM TEST. A

plug adapter.

m a n i f o l d vacuum test aids in determining the

condition of an engine and also in helping to locate

e. Connect timing light battery leads to battery

t h e cause of poor engine performance. To test

terminals.

manifold vacuum: C A U T I O N : S e t p a r k i n g b r a k e

f. If necessary, clean and mark the timing marks.

before attemptinq test.

a. Operate the engine at 1200 RPM until normal

operating temperature is reached.

g. Operate the engine at the specified idle RPM

and point the timing light at the timing pointer.

b. Install an accurate, sensitive vacuum gauge on

the fitting in the intake manifold. See figure 4-53.

h. If the timing is incorrect, loosen the

c. Operate the engine at idle RPM with the load

distributor hold down bolt and rotate the

disengaged (transmission in Neutral).

d i s t r i b u t o r until the desired initial advance is

obtained. See figure 4-52.

d. Check the vacuum reading on the gauge which

should be 18 inches or higher.

i . Tighten the distributor hold down bolt and

e . Check vacuum at maximum governed speed

check the timing again.

4-38