Timing -- with or without vacuum line ? (1 Viewer)

[rgentry]

I am trying to get my new (OEM) distributor set up. Seems like the
engine runs best when the timing is set well beyond 7 degrees BTDC.
Am I supposed to take the vacuum line off the distributor when I
am timing the engine?

My Haynes Manual states (pg. 97) "No variation in timing should be
obtained whether the distributor vacuum line is connected or not
at idle speed" I'm not sure I believe this. I thought that an engine
produces a lot of vacuum at idle.

It's kind of hard for me to test this statement as I have the old-timey
hard vaccum line that screws into the distributor.

 

[fjcruiser]

Yes, the manual says the engine should be timed to 7deg btdc @950 rpm w/ vacuum adv. cut. It says to disconnect the vac. lines and plug them.

 

[IDave]

Toyota F Engine manual specifically says to remove the vacuum line (and plug it). Everything else being correct (did you check the points gap AND the dwell angle of 41 degrees?) the standard 7 degrees BTDC should give you the overall best running at low elevations.

 

[rgentry]

OK. I trust the factory manual more than Haynes. 950 rpm
seems awful high though. I did learn by digging around that
the vacuum source that goes to the distributor is "ported"
vacuum and should be close to zero when the throttle plates
of the carb are not open (and they should be closed at idle).
I'll time the thing again tomorrow and report back.

 

[IDave]

From the F engine manual, it is 500 RPM (650 USA), not 950.

 

[Perfect Obsession]

First, on your OEM distributor, to know if vacuum hose(s) are changing timing, connect and disconnect them when idling. Don't forget to block disconnected hose(s), just in case. You could also disconnect hose(s) from the vacuum source.

By the way, FWIK, only two kinds of variable vacuum exist. From air path's point-of-view, vacuum hose could be:
- Connected before the throttle, ported vacuum. Give no vacuum when idling, and increase vacuum when accelerating.
- Connected after the throttle, intake manifold vacuum. Give maximum vacuum when idling and decrease when accelerating.

Note: Some anti-smog devices could be connected to these vacuum hose(s)

Reading:
Tuning with a vacuum gauge

 

[fjcruiser]

I was actually copying out of the manual, 950 rpm, although I never paid much attention to it. It actually reads 7deg BTDC/ Max 950 rpm. Idle speed is 650 rpm.
BTW this out of 2f manual, 1980.

 

[rgentry]

Perhaps centrifugal advance only starts at 950 rpm so it does not matter
if you are running a bit fast when you time it.