Help understanding advance curves

[sdyck]

Well to close the loop on my distributor situation, using a vacuum pump I confirmed my breaker plate appears to be sticking.  I get no vacuum advance until I get over 10 inHG, once I hit 20 inHG I get a maximum of 13 degrees of advance and expect as much as 18. The diaphragm in the actuator appears to be good as it holds vacuum.  I guess I will take it apart this winter to see if I can find the issue or replace, might be a good time to update to a 280ZX distributor to get rid of the points.

Thanks for all the help. 

 

Edited October 24, 2016 by sdyck

[Zed Head]

52 minutes ago, sdyck said:

 I get no vacuum advance until I get over 10 inHG, once I hit 20 inHG I get a maximum

That's actually normal behavior.  Nissan started putting both inches and mm on the X axis in the 1973 FSM's if you want to look at a few curves with those units.

[sweatybetty]

4 hours ago, sdyck said:

Well to close the loop on my distributor situation, using a vacuum pump I confirmed my breaker plate appears to be sticking.  I get no vacuum advance until I get over 10 inHG, once I hit 20 inHG I get a maximum of 13 degrees of advance and expect as much as 18. The diaphragm in the actuator appears to be good as it holds vacuum.  I guess I will take it apart this winter to see if I can find the issue or replace, might be a good time to update to a 280Z distributor to get rid of the points.

Thanks for all the help. 

 

i just pulled mine apart. there are 3 or 4 tiny ball bearings between the plates. they were all worn flat, and there was no grease at all. i put it all back together with new grease and it seems to move freely now. you might give it a try

[sdyck]

OK, now a final question and I'm afraid it might be a dumb one.

I understand you need to double the RPM and angle to get from the curve to get the maximum mechanical advance and similarly you need to double the angle for the vacuum advance, but you don't double the  inHg of vacuum number right? in my case the vacuum advance kicks in at 250 mmHG or 9.84 inHG  if I doubled it that would mean the vacuum advance doesn't kick in until almost 20 inHG and would top out close to 40. My test showed it kicked in at ~10 inHG and topped out at ~20. 

Sorry dumb question but I want to be sure since I think the breaker plate is sticking.

I will try and grease up the bearings, hopefully they aren't worn flat.

Steve  

 

 

[beermanpete]

No need to double the vacuum. This one is straigth up.