Setting ignition timing on newly assembled L28

[compression 38]

Starting a new thread here because I think this information might be useful to future people who try to do some searching.

 

Just got my L28 put together and up and running in my 240z.  This is a fresh install, pretty much all parts are brand new.  Engine was torn down to a short block, inspected, then put back together (rods, crank and pistons stayed in).  So it is essentially a fresh rebuild and I am just now getting running and dialed in.

 

Issue is that I am trying to set ignition timing and I am not sure if I am on the right track.

Parts being used:
-Electronic distributor (black box on side of distributor) - New

-New plug wires

-New spark plugs

-New SU carbs from Z-therapy

 

Car starts and runs fairly well, but just trying to get ignition timing locked down.

 

Here is what is going on:
It likes to idle at 20-ish degrees BTDC (vacuum advance disconnected)

Having trouble dropping the idle below 1000-1200 RPM, without it dying,  but that might be due to carb adjustment, still working on that. 

When I hook up the vacuum advance it sputters and dies almost immediately. When I watch the timing and hook up the vacuum advance, I can see it shoot to very advanced off the scale. 

 

A 280z service manual (what the distributor is from) tells me that the vacuum advance should be advancing it 9 degrees with 11"Hg of vacuum.  And mechanical (centrifugal advance) is 8.5 degrees at 1250 distributor RPM.

It also says base timing should be 10 degrees at 800 rpm (I assume that is with vacuum advance hooked up....) So I assume that with vacuum advance disconnected, my base 800RPM timing should be 1 degree advanced?

 

I did run it up to about 3000 RPM and set the total advance to about 30 deg BTDC, once again vacuum advance disconnected. Then bring it back down to idle and I hook up the vac advance and timing shoots up and it dies. 

What am I doing wrong here?

Should I just run without the vac advance connected? What is the downside? Input welcome. 

 

 

 

Thanks in advance (pun) for any help!!

 

PS:  I know I will have this solved in a few days, so I will try to follow up with whatever I ended up doing.

[xxmass 39]

I had similar issues with a stock 240. The problem was vacuume leaks. Once i had that sorted, carbs synced with ztherapy tool and dvd, issues were gone.

[xxmass 39]

Vacuum advance should be connected right on one of the carbs, not the manifold. When not in use should be blocked off.

[datzenmike 27,827]

If the idle is too high above the factory recommendation mechanical advance can creep in. Also where are you getting the vacuum advance from? There should be no vacuum advance at idle and why it should be from a port above the throttle plates. 

[metalmonkey47 1,473]

Disconnect vacuum advance completely from the equation until you've finished carb/timing setup.

 

I completely ignored base-timing on my 240Z, I set set timing to 30-degrees advanced at 3000rpm just as you did, and went through the carb sync procedure. Once you've gotten it idling correct and carbs sync'd properly, leave everything alone and drive it. The car drove amazing.

 

Make sure your chokes are disconnected when you're syncing carbs, that will effect idle if they aren't up all of the way.

[compression 38]

Well, this morning I realized that my throttle linkage was keeping the throttle plates from completely closing. So I adjusted the linkage and the idle screws on the SU carbs and now I am able to get my idle down under 1000. Still have the vacuum advance disconnected though.

 

I am grabbing vacuum from the port on the carb, as shown in this picture.

[Madkaw 195]

Your not going to be able to run 20 degrees initial timing and also run vacuum advance . If it’s the zx dizzy then 20 is good and DON’T use vacuum advance - just disconnect it.

The 8.5 number you read about is doubled when figuring mechanical advance . So 20 initial( no vac) + 17 mechanical =37 Nice number if you have good premium fuel . If you want to run the vacuum advance you need to run factory spec for initial

[compression 38]

Awesome info....thank you.

 

Your not going to be able to run 20 degrees initial timing and also run vacuum advance . If it’s the zx dizzy then 20 is good and DON’T use vacuum advance - just disconnect it.
The 8.5 number you read about is doubled when figuring mechanical advance . So 20 initial( no vac) + 17 mechanical =37 Nice number if you have good premium fuel . If you want to run the vacuum advance you need to run factory spec for initia