Distributor Advance

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Paul Hill

Active Forum User
Hi all,

Has anyone played around with the advance curves on the D609 type distributor?

What I have found out with having a play around is that it seems to be that my stock L24 running the standard HJG46W carbs tends to like more advance than the distributor will give?

The cam in the distributor has a maximum advance of 9 Degrees (18 Deg Crank) and all of this is comes in in a fairly linear curve up to 1800 rpm on the distributor (3600rpm crank). So with say 14 degrees of static and the total of 18 mechanical advance we have a total of 32 degrees. If I try to advance the distributor to 17 degrees static it starts to backfire lower down the rev range but pulls a lot stronger up the top end of the revs.

I'm thinking of milling out the slot that limits the advance in the distributor cam by an extra 1.3mm to give an extra 2 degrees advance on the cam (4 deg crank) that will gave a total of 36 degrees - I might have to play around with springs but having the distributor tester will certainly make it a lot easier!

Any comments or feedback on the thoughts above would be greatly appreciated before I get too deep!

Paul
 
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Paul Hill

Active Forum User
jonbills said:
Hi - no answers, only questions :)
Have you still got vacuum advance attached?
How sure are you of those static & mechanical figures? the chart here http://www.angelfire.com/fl3/DatsunZClub/ignition.html says 10 and 9 respectively.
Click to expand...

I have seen those figures before and I think they are what I saw in the Haynes manual? I have both the 72 & 73 factory service manuals and these give yet another set of figures!
(The vacuum advance is disconnected when measuring the timing on the car but I do put it back on and it only makes a difference at partial throttle opening (as expected). I did check the vac advance on the distributor tester and it was giving about 6 deg @ 250)

Ignition timing

1972 FSM states:
7 Deg BTDC @ 750RPM
Mechanical Advance Nominal @1400rpm (2800rpm crank) = 11 Degrees (22 crank)
Min / Max = 7 / 29 degrees


1973 FSM states:
17 Deg BTDC @ 750RPM
Mechanical Advance Nominal @1000rpm (2000rpm crank) = 6 Degrees (12 crank)
Min / Max 17 / 29 degrees

The interesting thing is that the cam in my distributor is marked up with 9 degrees!
 
P

Paul Hill

Active Forum User
Its been a long weekend and I pulled the wrong figures out of the 1973 FSM.....

Ignition timing

1973 FSM says:
17 Deg BTDC @ 750RPM
Mechanical Advanve Nominal @1200rpm (2400rpm crank) = 9 Degrees (18 crank)
Advance goes from 17 to 35 degrees
 
jonbills

jonbills

Membership Secretary
Site Administrator
Sounds like you know what you're doing. The fact that it's backfiring when you add static advance seems suspicious to me. On both my D609 type and the 280zx distributor I'm running now, I don't have the vacuum advance attached and I've taken a few degrees of mechanical advance OUT of it, so I can run more advance at idle. I set it at 35 deg all in, and I'm sure that leaves me with > 20 deg advance at idle. No backfires.
What sort of rev range are you getting backfires in?
 
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Paul Hill

Active Forum User
I think its around the 2-3000 mark - Next run out I will just pull the Vac advance off to see what difference that makes - I suspect there may be just a tad too much influence from this as it does have the capability of giving 14 degrees of advance!

I suppose that if that breaker plate does not get back to its zero advance position within a few milliseconds and you are up in the revs on full advance you could have something in the order of almost 50 degrees of advance albeit for a very short time !!

More testing needed but feeling hopeful..!

Thanks for your input :)
 
Luddy

Luddy

Well-Known Forum User
Hi Paul,

Rather than mill out for more advance, is it an option to rotate HT leads round one notch and retard to the max? I only ask be as I put a 280zx dizzy on my L24 and at full advance it was almost almost firing; the vac advance is broken on it so decided to stick with standard dizzy until I can fix.
 
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nospark

Well-Known Forum User
The 280zx distributors (which as you know is a recommended upgrade from a points distributor) enable adjustment of advance/retard by a bolt on the body of the distributor. But on the opposite hidden side of this bolt on the distributor body there is another bolt that you can adjust to give you even more advance. Is this extra bolt available on a 240z points distributor I wonder.
Perhaps this is not the point of your question or perhaps you are not chasing more static advance in itself but want to achieve more mechanical advance from your dizzy. Hope this helps
 
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