Timing Question

[Av8ferg]

On 2/16/2022 at 10:34 PM, Captain Obvious said:

Well I'm no expert on the subject, but my answer is "In theory, it shouldn't matter whether the vacuum advance line is connected or not."

Why? Because the source for the vacuum advance is a ported vacuum source that should provide no vacuum at idle. So, if your car is tuned and idling properly and your throttle butterfly is where it belongs when your engine is idling, then you should have no advance at idle. And because of that, it shouldn't matter whether that hose is connected or not.

However, if your car is out of tune in some way and you need to have the throttle open further than normal just to get the engine to idle, then all bets are off.

So, here's a way to check... Put the timing light on it at idle with the vacuum line connected. Then disconnect the line and see what happens. There should be no change in engine RPM and no change in timing advance.

He’s lying to you….he is an expert ! 

[Av8ferg]

The way I understand this after rebuilding my distributor.   You have 17 total degrees of mechanical advance with the 8.5 counter weights in the distributor (btw some have 9)  The engine rotates 2x for one distributor rotation.   This equals 8.5 x2 = 17 deg mechanical advance, and according to the FSM you should get full mechanical advance at 2500 engine rpm (1250 distributor rpm). Distributor vacuum advance should have about 10 deg of advance at 2500 engine rpm.   So at 2500 rpm you should have a total of 37 degs of advance and you can check that with a timing light by setting 2500 rpm and you should see the light flashing at 37.   If it’s way off of that at 2500 you could have issues in your distributor (breaker plate bearings missing or rusted) or a blown vacuum dash pot.  BTW….I’m definitely not an expert.  

[Captain Obvious]

1 hour ago, Av8ferg said:

He’s lying to you….

Remember Joe Isuzu? 

[cgsheen1]

I'm embarrassed to say yes, I do remember Joe Isuzu...

[Av8ferg]

I had forgotten about him but you have successfully dusted off some old brain cells. Isuzu kind of fell of the US map. That had some semi-cool vehicles back in the day. They should have never called that small SUV an Amigo.

[Av8ferg]

Checked my timing today with a new timing light that shows RPM. 10 deg at 800 RPM, 35 deg at 2500 RPM. Seems like my mechanical and vacuum advance are working are designed.