I have a 1975 F250 with 390 and Auto Transmission (early 1975, still has points ignition). I'm trying to adjust the dwell angle, but when I hook the meter up I get 15-17 degrees (set the points to 0.017" using feeler gauge). The book says 24-30 degrees. Seems pretty far off so I want to make sure I'm doing it right first. In the manual it says to crank the engine over, but everything I read says test dwell with the engine idling.

-Do I check dwell angle with the engine cranking over or at idle speed?
-Do I need to disconnect the vacuum hose to the vacuum advance or do I leave it hooked up?

Thank you.

 

Dad taught me to turn it over so that you get actual degrees req. with NO advance of any sort to alter the job

 

The dwell angle should be checked at idle. If the distributor is in good shape, advance should not effect the reading. You can check this by slowly bringing the rpms up to about 1200 and then slowly back down to idle. The angle should remain about the same, with no more than two or three degrees deviation. Dwell angle is the amount of degrees of distributor rotation that the points are closed. If it is too high, the contact-breaker gap is too small. If it is too low, the gap is too wide. Hope this helps!

 

Okay, thank you guys. I did a quick adjustment of the points and now it's closer to 25 degrees, so I think I'm good.