Request for Info: 2F Timing (Big Cap)... By The Numbers...

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Rocky_LC

Rocky_LC

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I was hoping some of you carb and ignition experts could chime in, and give me some information on the timing advance system by system.

I am running a desmogged 1985 2F in my '74 FJ40. I have all the stock ignition components (big cap dizzy and stock coil), a HAC Valve, and I tried to hook up all the vacuum plumbing per the "My Desmog Thread" in the FJ60 forum.

I got some info from this thread...

https://forum.ih8mud.com/40-55-series-tech/642818-install-60-dizzy-side-panel.html

What I wanted to know / confirm was:

Static Timing (at BB): 7 Deg BTDC

Max Total Advance Recommended*: ? Deg

* what do the experts recommend for total advance (mechanical + vacuum)

Max Mechanical Advance**: ? Deg

** what can the distributor deliver independent of the vacuum system

Mechanical Advance "All In" RPM***: ? RPM

*** what RPM should the distributor provide full mechanical advance

VACUUM SYSTEM

Max Vacuum Advance (Inner Port)+: ? Deg

+ How much advance can the Inner Port Provide at Full Vacuum

Max Vacuum Advance (Outer Port)++: ? Deg

++ How much advance can the Outer Port Provide at Full Vacuum. It should be the value above less 6 Degrees.

Vacuum for Full Advance (Either Port)+++: ? in-Hg

+++ What vacuum gives full vacuum advance.


I haven't ever seen this info broken out like this.


Thanks -

Rocky
 
I tried to measure some of this stuff on my own, but was having some trouble, as I could not see that there is any additional marks on the flywheel beyond the TDC (Line) and the BB (7 Deg BTDC).

More Questions:

At idle, I have 9" Hg of Manifold Vacuum. Is that lower than expected?

Outer Distributor Advance Port: 6" Hg Vacuum moves BB to edge of window (10 Deg??)
Inner Distributor Advance Port: 5" Hg Vacuum moves BB to edge of window (10 Deg??)
 
9" of vacuum @ idle is low. do you have a pix of the port that you measure out of? my dial in 18 @ idle.
I used the port on the intake (toward the front of the rig) Not sure how much advance i'm running but it pass the bb. I'm running a DUI unit and a 38 weber.

ps: I'm not an expert...
 
I agree that 9" is low. I'm around 17-18 at idle at sea level.
The old school timing guidance is to advance the timing until it starts to ping (under load) then turn it back until it stops.
In my experience, this is with the mark at around the edge of the window (on the advanced side) at idle with the vacuum advance disconnected. YMMV.
 
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yes, 17 for the vacuum is what I typically have

my big cap dizzy is almost maxed out for advancing before it hits - IIRC that equates to about 10 degrees
 
Specs for stock 81-87 USA distributor:

Max Mechanical Advance- 21*

Mechanical Advance "All In" RPM- 4000

Max Vacuum Advance (Inner Port)- 18-20*

Max Vacuum Advance (Outer Port)- 6-7*
 
Thanks, Jim. I will print this info out, and keep it close to my truck.

Now back to figure out why my idle vacuum is so low. I'm wondering if that's real... It seems hard to screw up that measurement, and the truck runs "pretty good", it doesn't SEEM like I have a major vacuum leak.....

One thing I thought was a little interesting was that my idle actually speeded up by about 4-500 RPM if I left the distributor port open to the air at idle. I don't think this was due to Vacuum Advance, but maybe to leaning out the mixture a little? Is this normal?

When I plugged the hose with a golf tee, the Idle dropped back down.

Thanks -

Rocky
 
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FJ40Jim, is that same info available for any other vintage distributors (i.e. '74)? That would be greatly appreciated.
 
(bump, I know)

Jim, do I read that correctly that the total advance for a carbed truck is 52-55 degrees?
(7 static + 21 +18 + 6)

Thanks,

t
 
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