Timing Question

[HappyZ]

I've read many of the posts, but never found reference to the vacuum advance.  Do I plug the advance when setting initial timing?

Edited February 16, 2022 by HappyZ

[Captain Obvious]

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.

[HappyZ]

Thx…I’ll try it today

[Captain Obvious]

Cool. Hope everything works out as expected.

So out of curiosity... It seems you've got an L28 in your 240Z. Are you running carbs or the L28 fuel injection system?

[HappyZ]

Carbs with points … switching to electric points soon.

[SteveJ]

If you're tuning with points, do you have a good dwell meter? I once tried 3 dwell meters on one car and got 3 different readings. (To make it even more fun, the distributor was missing one of the adjustment screws, so I had to wing it while adjusting it.) I since got a 4th dwell meter so I could confuse myself more. The old school dwell meters are NLA. I might eventually break down and buy a Fluke 88V. I think it will measure dwell, and I only have about 8 or 9 multimeters, so there is a need to buy another meter.

Once you switch over to an electronic ignition, you can probably retire the dwell meter. Sometimes I still work on a luddite's car, though, so I'm keeping them around.

[HappyZ]

Thanks for the tips.  I’ll go straight to electric points so i don’t have to buy another meter as well haha.

[Captain Obvious]

You could run the "pull the hose off and look for differences" now. That way, you would know if it really mattered before you threw another variable into the mix.

In other words... When your car won't start after the points conversion (because of some detail somewhere), you may know if it could potentially have anything to do with the vacuum advance system. Or not.  

[HappyZ]

I'll do the pull the hose routine and report back tomorrow.

thanks to all

[HappyZ]

@Captain Obvious I set timing 10 at 800 rpm with vacuum connected.  I then disconnected and plugged the vacuum hose.  There was no change in timing.  I then reconnected the vacuum and rev’d the engine…the timing advanced.  It appears it’s working as advertised.

I did notice that whenever I rev’d the engine, it would die when I released the throttle.  It was sort of a smooth die where the rpms drop smoothly and then it just stops…No sputtering or attempts to keep running.  It idles good when I restart.  Perhaps my floats aren’t set correctly?

Edited February 18, 2022 by HappyZ

[Captain Obvious]

Cool. Good to confirm that your vacuum advance isn't doing anything at idle and that it does work when you rev the engine. Sounds perfect.

As for the stalling on throttle release... Long standing automotive issue. First thing I would do is check the mixtures. I've seen that dying at idle and a hunting idle when the carbs are running rich.

[kully 560]

if it does advance when rpms are increased that is also the mechanical advance, and the vacuum advance still might not be working.