Distributor and Timing Help.

[Hardwyre]

'76 280Z. First Datsun ever.

 

Previous owner said the head was rebuilt; sweetness.

 

I added an MSD 6AL ignition with Blaster II coil. Seems to have helped flatten out the torque curve.

 

I adjusted the timing to the factory 7 degrees cold, which seems to crawl to about 12 degrees when warm. What is the deal with the dual-timing dizzy? Is it the CA type? I'll pull numbers off of it today.

 

Braap gave me some awesome advice for initial timing, setting it around 15 to 20. Here's the rest of his post to me:

The car was daily driver, 75 280-Z that also saw Autocross duty. Full interior, etc. Weighed right around 2800 lbs with driver and half tank of gas. Tires were nothing special 195 60 HR14" tires. Stock open 3.54 ration R-200 diff. Trans was a '78 5 speed. Stock low compression '75 block, stock '77 head that ported and unshrouded the valves dropping the compression even lower! Stock '78 camshaft EFI was stock but spent years finely tuning. Ignition was the stock '75 with Jacobs wires and Jacobs coil, multi electrode spark plugs and recurved advance. Header and dual 1.75" exhaust, got 30 MPG, swapped to dual 2" exhaust best mileage dropped to 28 MPG. This car ran 0-60 MPH in 5.7 seconds and did the 1/4 mile in 14.4 @97 MPH.

 

The real magic is in the tune. These engine love lots of ignition timing. Max Mechanical advance, (vacuum advance disconnected), was 42 degrees, full in by 2000-2200 RPM. Be sure your vacuum advance is also hooked up AND works! That is where most of your fuel milage comes from. I would see as much as 52 degree ignition advance at part throttle cruise and the engine loved it! If your ignition is bones stock and you are not real familiar with setting full mechanical advance, just set your ignition timing at idle between 15-20 degrees. With premium gas, you should be able to run maybe even more than 20 degrees at idle! So long as the engine does not ping, keep adding more ignition advance. When it start to ping, retard the timing back a couple/few degrees and leave it. You will notice the car will be a LOT snappier, more powerful at all RPMS, wont need as much throttle to cruise down the freeway or around town and your mileage will also increase dramatically. AGain, be sure your vacuum advance is functioning as it should. With out it, your mileage will be terrible, like you are getting currently. AFter that is fine tuning your EFI as covered elsewhere on the forum.

 

I've been trying to find information via the search button for setting the mechanical and vacuum advances, and while mech.adv seems to be controlled by bushings and weights, I can't find anything instructions for adjusting the vacuum advance.

 

Also, do I set the timing cold or warm as it differs. I'm assuming let the engine warm up first.

 

I am thinking are starting with this profile:

 

20 initial

36 mechanical

## vacuum at part throttle.

 

Am I correct in understanding that vacuum advance will take the timing beyond the 36 "all in"?

 

Does vacuum advance work like this: At partial throttle, manifold vacuum is high, raising the advance(~50BTDC) to allow for better mileage, but as you open the throttle, vacuum drops, leaving only the mech.adv (~36BTDC) and creating more power?

 

I noticed something else; when I changed the cap and rotor, the contacts inside the cap looked like they'd been gouged or sliced. I was initially thinking it was spark decay, but is it more likely this is a sign the dizzy is wobbling?

 

Oh, does anyone have information of adjusting and fine tuning the EFI? I keep finding information for tuning MegaSquirts.

[rjstcroix]

Hey,

 

Here's a link that will help you understand a little more about the vac. advance.

 

Enjoy!

 

RSC

 

http://atlanticz.ca/zclub/techtips/timing/index.html