Noobie; '72 240z running a zz4--stumble on tip in

[jvandyke]

poked around a bit tonight, interesting findings;

fuel pump circuit: one of the two wires on the oil pressure sensor had fallen off (probably due to us messing with the distributor) fuel pump works steady 7psi of fuel now

feeling exhaust after brief test fires and several cylinders are obviously not firing, every other cylinder in the firing order: 2,5,3,8, they have spark and compression so, bad coil?  We swapped in a new one off some random HEI distributor I had bought 2 of (for an old Ford) and never used the one.  I went to put the old one back on but it's center button totally fell apart.  Hmmmm,

I did a compression test on #3 it was fine, didn't do the others but can go back out in a bit, weird. 

After some googling: one side of the carb isn't putting out.....maybe.

Edited September 11, 2018 by jvandyke

[Miles]

Again checking out the ignition system requires a methodical component by component  approach.

 

Make a list of every ignition component and verify condition and function.

 

Do you have a spark at each plug wire?  

 

One side of the carb not working?

 

 

Do you have a manual for the engine?  If not get one .

 

 

[jvandyke]

So I went out again last night, after finding other guys with a 2,5,3,8 no fire. Most claim carb issues. I had already checked for spark on those with a timing light and we had it.  I went to check carb settings and found the primary dumped gas as I opened the inspection port so I reset that float but didn't have time to check operation.  I think we introduced a lot of little issues as we went after the initial rough running, dying on acceleration.  Cautiously optimistic that the flooded primary side was a major issue.  I had checked it before and it seemed fine but that was during the intermittant fuel pump saga so, well, lot's of factors ganging up on us.

Manual: they make them for crate ZZ4s?  Heck yes I'll hunt one down.  I assumed I would have to fumble about in the dark on that.

[Miles]

Do you know about the clear site glass on the fuel bowel for adjusting float level?

[jvandyke]

No, I don't.  There's a brass plug.

Test fire, no joy.  Pulled primary bowl, can't see anything amiss.  2,5,3,8 still not operational.  Spark was weak with timing light. Then gone. ???  I STILL don't know if it's carb or ign. 

[Miles]

If you had the Holley manual you would know that Holley sells a clear sight glass that allows visual setting of the floats. No wonder why you are having a hard time  with the carb

 

Download the Holley pdf for your carb and read it!

[jvandyke]

I've got the Holley manual, practically memorized by now.  

[Miles]

 

[bunkhouse]

 I'd work on the ignition until you get a good hot spark on all cylinders then go back to the carb.

[jvandyke]

I think I agree.  Not firing (or weakly) to every other cylinder in the firing order is just too weird.  I'll swap coils around, triple check static timing and all else ignition related.  We'll get there.....again.

[Michael]

1-8-4-3-6-5-7-2 (GM firing order)...  In your case, every other cylinder is non-firing?  Such systematic failure is peculiar.  HEI module?  Is there a spare distributor, to replace the current one (the complete thing)?

[jvandyke]

It was carb related, I still don't know what happened but the Holley was flooding the left bank of the dual plane intake, flooding 3/5/2/8 (by memory) which are fed by the left side of the intake.  I stole the Edlebrock 1407 off my '62 Galaxie and she fired right up and ran great.  I've been through the Holley 4 times and can't figure out what is up, warped metering block, something crazy, I replaced every part to no effect.  Might get one of these if I can't find what's up with Holley

https://www.summitracing.com/parts/sum-m08600vs

I think the spark issue was just the plugs starting to foul.  I always assumed the timing light would fire when on a wire even if the plug wasn't sparking, someone set me straight on that.  All ignition efforts were unrelated but we have a new cap and rotor.

The Holley is messed up that's for sure.  The old girl wants to rip it up with the Edlebrock on there, although I suspect it's too much for this motor being a 700cfm carb but it'll get the groceries home anyway until we can either sort the holley or find a replacement.

Edited September 18, 2018 by jvandyke

[jvandyke]

So what went wrong first I don't know but in the re-re-rebuild I put the wrong meter block gasket on and that induced serious flooding.  That sorted it out.  Then we starting battling the choke, long long story but the end is a manual choke and I had to modify it.  End result is we're running strong again.  Now try to get some heat as it's getting cold around here.

[Michael]

Congratulations on a successful resolution!  It is indeed frustrating, how one might spend years on remediating rust, building a roll cage, inserting new frame rails, building an engine, etc., only to suffer deep disappointment because of some minor but insidious problem with the tuning (spark and/or fuel).  But this happens often.  Even if we can't diagnose the problem, and only solve it by swapping parts, well, at least the problem has been solved.

 

Given your stack of receipts, perhaps you can do some sleuthing on the provenance of this engine... its parameters and properties.  From that, it would be possible to select the "ideal" intake manifold and carb.  And then maybe the final step would be tuning on a dyno.

[jvandyke]

Yes, we should try to figure it out.  There’s a slew of receipts from the initial build back in ’95-’96 but not much since.  It used to have a little higher cfm carb, who swapped it out when and why I don’t know but they didn’t do it very well.

My kid has been driving it for a few weeks now.  We got some heat going and she’s running decent.  We have to go after an exhaust leak at the header.   He’s content to be going to high school in a 48 year old classic hot rod.  So am I.  I think we’ll get it sorted better over the winter, clean up the interior, tweak the tuning.  We have to do something with the suspension, it rubs.  Maybe even do a little dragg’n.  It's a hoot to drive as in but I think we should tame it down a bit, make the fuel pump quieter, weather stripping on the windows, maybe even get the A/C working again.