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720 timing marks- pic needed


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#1 Pacific coast Datsun

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Posted 01 February 2010 - 09:13 AM

Was wondering if anybody has a pic or knows what the timing marks are on the plate that comes off the block ?
It's on a 85 720 with the Naps-z motor.
Also if anybody knows what mark on the crank pulley that indicates 0 TDC ?

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#2 datzenmike

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Posted 01 February 2010 - 05:36 PM

The timing scale is bolted onto the timing cover on the right side near the alternator. Each point to point or valley to valley distance is 5 degrees.

Posted Image

The pulley will have a very small notch in it that passes the 20 10 and 0 (TDC) marks in a clockwise or left to right direction. Mark the notch with white paint and using a timing light set the advance just to the left of the 0 at the 3 to 5 degree before TDC position.

Pulley notch looks like this and is small.


Posted Image


Posted Image

#3 Pacific coast Datsun

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Posted 01 February 2010 - 08:47 PM

I just knew you'd have the pics Mike :D I ended up taking sandpaper to the timing plate to make the #'s visable. Thanks again Mike.

85 720--74 pl 620--94 D 21-- 64 L 320 [co-owner]--74 sundance 16 jet boat [L 20 powered]
Member- *Japanese trucking association*
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#4 datzenmike

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Posted 01 February 2010 - 09:26 PM

I didn't have pics, so I went outside and shot my truck. I bought it out of an '84 720 but when I got it home and removed the tranny it was actually an '88 Z24i.

#5 Pacific coast Datsun

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Posted 02 February 2010 - 02:20 PM

TY again for the pix Mike. Im helping a friend tune his 720 & we wanted to set everything to factory specs. Set timing @ 3btdc & the idle @ 900..test drove it & it's sputtering & runs like crap.
When we put the timing back to what it was..14 btdc & the idle back to 1200 it runs great :huh:
Any idea's ??

85 720--74 pl 620--94 D 21-- 64 L 320 [co-owner]--74 sundance 16 jet boat [L 20 powered]
Member- *Japanese trucking association*
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#6 datzenmike

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Posted 02 February 2010 - 06:08 PM

Absolutely! I'll bet good money that one of your coils isn't firing. Pull the coil leads off the cap and put an old plug in the end and lay on a grounded surface and crank the motor. If one isn't sparking replace the second fuse over from the left hand side on the fuse box.

Once you get spark from both coils re time for 3 to 5 degrees and it should run better.

#7 Pacific coast Datsun

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Posted 02 February 2010 - 07:05 PM

Ok didnt even think of a bad coil. Will check it tonight or tomorrow & report back. Basically we need to get it to pass smog so the truck can change owners... ;)
another question....when we set the timing do we have to discocnect the vaccum advance hose @ the dist.?

85 720--74 pl 620--94 D 21-- 64 L 320 [co-owner]--74 sundance 16 jet boat [L 20 powered]
Member- *Japanese trucking association*
*Southwest Datsun pickups*
http://www.southwestdatsunpickups.com/
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#8 datzenmike

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Posted 02 February 2010 - 08:02 PM

All Nissan carbs (since 70 at least) have ported vacuum to the dizzy. The port is above the throttle plate, so at idle it is receiving outside atmospheric air pressure. (no advance) As long as it is warmed up and idle adjusted you can set the timing just fine.

Idle... no vacuum advance. But as soon as you give it the gas, the throttle plate rises above this port and applies vacuum to the distributor, advancing it.



Removing the vacuum advance at idle is a crappy but effective way to reduce emissions (but only at idle) and that is the only reason for this. Before emission controls, all ignition timing was set with the hose disconnected so that the static timing could be set, then the manifold vacuum was connected and the distributor advanced. It ran smoother and cooler at idle... but polluted.

Next time you set the advance on your L series motor, note how well it idles at 750? Then twist the dizzy slightly clockwise to advance it. What happens? It will rev up and run smoother because all engines need and want more advance at idle. Of course you can't run it there because the dizzy advance is designed differently for this and will add too much advance causing it to ping under load. The point is, motors want more advance at idle but are run slightly retarded for emission purposes.

#9 Pacific coast Datsun

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Posted 03 February 2010 - 05:54 PM

Ok turns out both coils check out ok. The current owner adjusted the air-fuel screw on the carb a bit, set the idle @ 1000 & timing @ 3 btdc & he said it runs alot better.

85 720--74 pl 620--94 D 21-- 64 L 320 [co-owner]--74 sundance 16 jet boat [L 20 powered]
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#10 datzenmike

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Posted 03 February 2010 - 06:49 PM

The leaner the mixture the more advance you need. The '85 carb was adjusted at the factory and a plug put over the adjust screw. The po must have drilled it out. Try and get the mix right and the idle down around 750?