Setting Ignition Timing

[ramsesosirus]

I've looked in various places, done searches, all that stuff.  The FSM is surprisingly vague about the ignition timing adjustment procedure.

The car is a stock 76 280z, so it has the vacuum canister on the side of the distributor that has a "T" connection also.

I just want to set my timing.  Auto Trans.  

I know you want the engine warm, verified correct idle (700 rpm for auto in D, 900 for manual).  

 

After the engine is warm, do I unplug and cap the vacuum hose from the distributor, (assume cap the canister AND the hose...)  and then it the timing should be 7 degrees BTDC?

Or is the vacuum hose supposed to be connected to the distributor when you get the 7 degrees??

(The sticker under the hood says 7 degrees, but I've read most like 10 degrees initial....)

 

This is a somewhat irritating question to have to ask, however I cannot seem to find a concrete answer to this.  I've played with rotating the distributor to adjust, and I can hear it change.  But I don't want to damage this engine with such a seemingly simple setting.... especially when it should be simple to determine the correct procedure.

Apologies for such a newbie question....

[siteunseen]

I've always plugged the hose and set mine at 10 degrees BTDC, but that's on a manual transmission.

If you don't plug it you'll be creating a vacuum leak.

I don't plug the distributor's hole, just the intake manifold's.

[siteunseen]

My sticker says 10 BTDC on my '77 5 speed, just ran down and checked.

[ramsesosirus]

Thanks, my sticker says 7 degrees for a non-Cali 76 auto,  but i'd like to go with 10 (I've read L28's like a little more advance:  the "factory" timing is for best emissions so I've heard...)

And I didn't really think about it, but you are right.  I would only need to plug the vacuum line or port, since the canister on the distributor doesn't actually create vacuum, so leaving it "open" (with the line plugged) wouldn't actually create a leak.  Makes sense.   

 

[Zed Head]

You should find that no vacuum is pulled at idle, at the hose connection.  The vacuum advance port should be "ported" vacuum, it only gets vacuum when the throttle is off-idle.  That's why Nissan doesn't mention it, I think.  On page ET-6.

[siteunseen]

Yes, it's ported.  Intake vacuum drops when the rpms go up.  Sorry, I assume the only reason to plug it would be the vacuum leak.

[Zed Head]

Actually, it's just shut off completely.  The hole in the throttle body is covered or on the other side of the throttle blade.  Can't remember which.  Just one of those weird things that can start pages of forum discussion - ported or constant vacuum advance supply.  Google will give many pages if you try that phrase.  Nissan went with ported, at least for EFI.  I think it gives cleaner emissions and a steadier idle.

[siteunseen]

Do they call it ported because it's on the left side of the throttle plate?   Just kidding, its on the left if you're looking at it from the passengers side, I think???  It's gotta be behind it, right?  If the butterfly is closed there won't be any airflow,  I would think.

I'm leaving now, I've worn out my welcome. But have beer cans for sighting in my squirrel sniper rifle tomorrow.  They're a problem where I live. They chew up more than my puppy but I can't shoot him. 8^)

[ramsesosirus]

Hmmm....how am I "supposed" to set the idle speed first, before adjusting the timing, when adjusting the timing seems to effect my idle speed???

If I get the idle speed correct (700 rpm in D for automatic trans), then move the distributor to adjust the timing, the idle speed changes, and sometimes I have to loosen that set (spring loaded on TB) screw to keep the car from nearly dying?   

[Zed Head]

That is the way top do it.  Iterative.  Actually, the main reason they want idle speed to be low is so that the mechanical advance weights aren't advancing the timing.  So it doesn't have to be exact.  You'll probably find that you adjust the timing, then the idle speed, and the timing doesn't change, because it's below the activation RPM for the mechanical advance.  If timing moves a lot at low RPM then you probably have a broken/weak spring in your distributor.  You shouldn't get any change in timing until 1200 RPM.  Specs. are in the Engine Electrical chapter.