Vacuum advance part identification

[inline6]

Does anyone know what these letters and numbers ink stamped onto the vacuum advance mean?  I see a lot of different combinations on the parts I have seen for sale.  A lot of times, there is not vehicle specific applications listed.  Are these just date codes?

  

I'd like to replace the original vacuum advance on my Euro 240z distributor, but I won't have much luck looking for that part by application.  

I bought a new vacuum advance that "looks correct"; however, when I hook up the vacuum line to it with the engine operating, the engines revs and dies repeatedly.  I am running a Pertronix ignition pickup, which may matter.  And I plan to do some testing on the new vacuum advance as well as my old one which is still functional. 

But, it would be nice if I at least knew what I was looking for in a replacement vacuum advance.  

 

[inline6]

I reinstalled the original vacuum advance that came with the Euro distributor when I bought it about 30 years ago.  It still holds vacuum when applied with a tool.  So, I primed and painted it (silver).  I'd still like to find the correct replacement (yellow chromate/zinc).  

With it installed, the engine does not rev and die like it did with the other one (NOS but of unknown application).  The shaft that the spring goes on is both longer overall, and longer when it is fully pulled in by the vac adv diaphragm.  So, there is that known difference.

I guess I will keep looking a replacement original part "22301-E4601".  But, it would be nice to have more knowledge about these original vacuum advances, so I might have a better chance at finding one that would be a suitable replacement (with swapping the linkage parts).

[Captain Obvious]

On 11/9/2024 at 9:56 AM, inline6 said:

I bought a new vacuum advance that "looks correct"; however, when I hook up the vacuum line to it with the engine operating, the engines revs and dies repeatedly. 

I don't have any input into identification of what would be the correct advance canister, but I'm a little puzzled by the reaction you had with the one you tried.

At idle, the vacuum advance should be doing nothing. In fact, you should be able to connect or disconnect the vacuum line from the canister with no noticeable effect. The vacuum source is a ported source, and there should be no vacuum in the hose when the engine is at idle.

I'm not sure why your engine wanted to rev and then die. 

[inline6]

55 minutes ago, Captain Obvious said:

I don't have any input into identification of what would be the correct advance canister, but I'm a little puzzled by the reaction you had with the one you tried.

At idle, the vacuum advance should be doing nothing. In fact, you should be able to connect or disconnect the vacuum line from the canister with no noticeable effect. The vacuum source is a ported source, and there should be no vacuum in the hose when the engine is at idle.

I'm not sure why your engine wanted to rev and then die. 

Me either.  I am not certain that either the correct vacuum advance, or the NOS (and incorrect) one does nothing at idle.  The proper way to set initial ignition timing is to disconnect the vacuum advance, yes?  

Separately, I have always wondered why the timing specs are at RPMs that are "too low".  For my Euro distributor, the spec is 17 degrees BTDC at 550 RPM.  To achieve that low idle speed, I have to unplug the vacuum advance unit and seal the tube to the intake manifold, mess with the throttle plate screws on the SU's to lower idle speed, but  keep the front and rear carbs in sync.  Then set timing at 17.  And finally, bump the idle speed up to something a bit more pleasant (750 rpm).  And reattach the hose to the vacuum advance.

By the way, disconnecting the NOS one solved the rev/die situation.  And with the correct vac advance and linkage bits, the engine is not doing that.  I suspect that the Pertronix unit didn't like the amount of movement the NOS vac advance was causing.  

I will be checking (as best I can) the timing advance as the engine revs soon. 
 

[Zed Head]

1 hour ago, inline6 said:

The proper way to set initial ignition timing is to disconnect the vacuum advance, yes?  

Not with ported vacuum.  Ported vacuum sources pull no vacuum at idle.  So there's no need to remove the hose.

I've never found a good description in the FSM's of where Nissan sourced the vacuum for the distributor advance.  Most emissions era cars would use ported vacuum since it gives retarded timing advance at idle, and retarded timing is cleaner.  You can tell if it's ported by just removing the hose while the engine is idling.  If nothing happens, it's ported vacuum.

It's always been a hot topic.  

[inline6]

17 hours ago, Zed Head said:

Not with ported vacuum.  Ported vacuum sources pull no vacuum at idle.  So there's no need to remove the hose.

I've never found a good description in the FSM's of where Nissan sourced the vacuum for the distributor advance.  Most emissions era cars would use ported vacuum since it gives retarded timing advance at idle, and retarded timing is cleaner.  You can tell if it's ported by just removing the hose while the engine is idling.  If nothing happens, it's ported vacuum.

It's always been a hot topic.  

I just set the ignition timing on my car yesterday using the process I described above.  I could warm the engine up, check the timing with a light with the ported hose connected to my vacuum advance, and see if the setting is different than what I set it to yesterday with the hose disconnected... 

There is vacuum present at the rubber hose (to vac adv. assembly)  - I verified that yesterday.  It is slight.  Perhaps it is too little to cause movement at the plates in the distributor at the present idle speed.  Easy enough to test.



 

Edited November 11 by inline6

[gundee]

I use manifold vacuum on my 240Z.

Unplugged it is set at 10 degrees BTDC.

When plugged in the timing jumps to 17 degrees BTDC. Perfect.