5 hours ago, Jughead said:

Gentlemen, Here's the latest update:

1)      I redid the compression test using with better tester and throttles open.  The readings look good (to me):

1=165   2=160  3= 174   4=170   5= 160   6=165

 

2)      I removed valve cover again to recheck cam sprocket position @ TDC on compression stroke.  Please see new pics below, and give me a sanity check on the following:

a.       The notch on the sprocket is directly below the groove, on the camshaft locating plate.  (This is factory setting, per Haynes).

b.       The distributor/oil pump shaft “tongue” seems to be positioned correctly. (I did confirm that distributor shaft was NOT installed 108 degrees off!)

c.       The #1 cylinder cam lobes are in the “bunny ear" position 

d.        I used a zip tie to verify TDC, and checked that the rotor was in #1 position to verify I was on the compression stroke. 

e.        Question: Should I be concerned that the #1 mark on the cam sprocket is not on the “bright” light. (It looks to be on the adjacent one.)  I have no idea whether the other bright link is correctly positioned on the Crank sprocket.)  Everything else seems to be spot on...

 

3) Hooked up vacuum gauge and, after adjusting timing and mixture,  I got between 19-20 psi of vacuum.  The engine "purred" at these settings (at idle).  And yet, when I test drove, I got backfiring & sooty plugs (again).  And (again), when I adjusted to lean out, I got backfiring (i.e. "front-fire") out of the carbs. I've sprayed starter fluid on the manifolds and didn;t notice any reaction.   

So now I'm focusing on the distributor.  I'm looking for a new/rebuilt dizzy to swap in & see what happens.  Anyone have a solid distributor they'd like to sell?    I also need a cam oil spray bar ("oil distribution tube").

Thanks all, for hanging in there with me!!!  Jughead

 

Ignore the bright link . That dizzy spline should be at 11:25 o’clock . Looks like yours is at 12 noon . 

Need more background info . Did you rebuild the engine ? Did it run right previously? 

4 hours ago, siteunseen said:

No you do not.

Zed Head helps so many people in different threads it gets confusing sometimes. I do it all the time.

Oops.  

On 3/28/2021 at 7:22 PM, Zed Head said:

Like madkaw says, vacuum leak probably.  You're tuning at idle for the leak, then when you get on the throttle the leak has less impact and your tune is wrong.

I'd try to add your post about the whistling and clicking at the intake manifold but multi-post quotes on this site are difficult.

Your symptoms still sound like the "lean problem",  just for carbs.  Don't know if it's your throttle blade shafts or intake manifold gaskets but it seems to fit.  The SU's might be even more susceptible to vacuum leaks because of the way they use vacuum to raise the pistons.

Anyway, everything else looks pretty good.  Don't know if your oil pump shaft is off or not but you said that ignition timing was correct. 

 

14 minutes ago, Zed Head said:

I'd try to add your post about the whistling and clicking at the intake manifold but multi-post quotes on this site are difficult.

Your symptoms still sound like the "lean problem",  just for carbs.  Don't know if it's your throttle blade shafts or intake manifold gaskets but it seems to fit.  The SU's might be even more susceptible to vacuum leaks because of the way they use vacuum to raise the pistons.

Anyway, everything else looks pretty good.  Don't know if your oil pump shaft is off or not but you said that ignition timing was correct. 

 

Not enough history here . Did this motor ever run right ? Did this happen only after the carb work ? 

It would be nice to swap out with a known good dizzy . Maybe the shop fried your ignition when they installed it . Did it run okay after they put the Pertroni  in?

@Zed Head /All:  Here's my complete history with this car so far...

First of all, about me:  I’m no “expert” mechanic, but I’ve done many repairs over the years, including replacing a tranny & a cylinder head, starters, suspensions, etc. – simple stuff mostly though.   

I bought my Z car about 2.5 years ago.  The previous owner told me that he & his mechanic “could never get the carburetors adjusted right”. (Hmmm).  It had been under a tarp and not driven for at least 10 years prior to my purchase.  

Most of my time with the car has been spent doing body work (in all the usual places).

Last summer, after changing all the fluids and filters, I started her up and had a couple weekends with the car running awesome. It was great!  Initially, there was some crap in the fuel lines, but that cleared up after a couple  fuel filters.  I put 50-100 miles on it, but then it started to run poorly (ran rough, low power - thought it was running out of gas.)   It turned out that one of the chokes was stuck down, so I cleaned it and it ran great for another 50 or so miles.  Then I had similar problems with the other choke which I fixed as well. 

Soon after that though, I had it running smoothly in my driveway, and as I was looking looking down at the exhaust, it suddenly just stopped running.  Dead.  Turned over, but wouldn’t start.  I checked the chokes – they looked fine. 

So, just to get it started, I put in new points, plugs, condenser & coil.  Wouldn’t start 

So I rebuilt the carbs – very carefully - using the Z therapy videos and LOTS of coaching from Steve Epperly at Z Therapy.  I’m 99% confident that they’re rebuilt & set up correctly.  I’m on the list for rebuilt carbs, but Steve’s skeptical that carbs are the issue.  (HUGE shout out to Steve by the way!)

Last year around Christmas time, it was getting too cold to work on it, so I brought it into the local shop.  They were trying to diagnose it, when I got a Pertronix system for Christmas.  They suggested they install it to see what would happen.  They installed it, and got it to start, but it’s had the symptoms described above ever since...  

A couple of other potentially interesting details:

1)     When I changed the points, the distributor was pretty dirty, so I pulled it to clean it and bench-install the points.  The distributor slipped into a shallow tub of EvapoRust and was partially submerged overnight.  I blew it out with air, and it seem to spin ok, so I forgot about it.   I haven't taken it apart yet...

2)     At one point I replaced the ignition switch with an old, used one that came with the car.  I can’t remember exactly why I did that, but as I recall, I was not getting enough voltage to the coil, so I tried it.  (This was around the time of,  but prior to, replacing the ignition parts.)  It ran fine for a while after I swapped out the ignition switch,  but I’ve wondered if this might be part of the problem…

3)     Based on many conversations with Steve Epperly, he recommends swapping the distributor with one with points as a test, which I’m currently trying to source.  

So, that’s my story.  Other than swapping the distributor and rechecking the manifold gaskets, any thoughts?  I WILL figure this out,  but I want to do it while I'm young enough to drive it!   I’ll take all the help I can get…Thanks Y'all!

Edited April 5, 20214 yr by Jughead
clarification

I'll throw a wild guess out - check your grounds.  Distributor to block, block to battery, etc.  Might be that when people are messing around with the distributor that they disturb  a bad ground and it gets better for a short while just from the movement.  Good spark is all about a good circuit, good current flow, through the coil, and that goes through the ignition module or points.  Since it ran well once, and the good stuff happens after somebody messes with the distributor, and others have focused on it, that seems possible.  That's why Nissan adds a separate dedicated ground wire to the distributor body, even though it's already bolted to the block (actually the timing cover).  Grounds are the secret cause of many problems.

@Zed Head: Thanks - I'll do it.  Is there a comprehensive list of grounds to check for a '72?  I'll definitely check out those you called out above  .

BTW:  Is the that little (~ 3" braided) wire the only thing that grounds the points?  Where (on the distributor) would you attached a secondary ground?  Thanks!

I grounded mine to the screw that holds the condenser, over to a coil mount bolt. Then a bigger wire from the coil mount bolt to the battery directly. 

 

The points ground from the advance plate to the body through the internal wire.

 

Also look for cracks in the plastic isolation pieces as they can short out too. 

 

 

 

Edited April 6, 20214 yr by Terrapin Z
damn autocorrect.