NAPS Z24 camshaft issues

[datzenmike]

No. The exhaust side shut off only occurs at low vacuum under heavy throttle higher RPMs. It can be defeated by simply unplugging the white wire going to the dizzy.

 

The distributor only runs on ported vacuum from the carb. The hose from the intake is actually from a thermal switch that, when cold, is a vacuum leak so that the dizzy does not have vacuum advance when the motor is cold. When the motor warms up this vacuum leak is closed and the dizzy now gets full ported vacuum. Simple.

 

The anti dieseling solenoid only affects the flow of fuel to the idle circuit. It's purpose it to shut off fuel when the key is turned off to prevent run on. It has no effect on running above idle. Does your 32/36 even have one??? If so it needs 12 volts from the ON position on the ignition switch.

 

When tuned with a vacuum gauge and by ear, the timing was way advanced according to timing lights(the lights said 22 degrees advanced when it ran the best). When I lowered timing closer to the stock spec, it bogged so bad it had no acceleration at all until after 4k+ RPM...and if you set the timing at 8 degrees of advance, you could kill the motor by stabbing the throttle. When I run the timing close to stock spec, it has much less power and kills my gas mileage...if I run the timing high enough to get the best performance and gas mileage, the motor kicks back when I try to start it when it is warm, and it diesels(runs on) after you turn the key off.

 

 

22 degrees is impossible so you readings are suspect. Timing by ear is your best bet. Run it where it runs best.

 

A big cam is going to run like crap at low speeds so expect this.

 

Disconnecting the EGR will have no effect on running unless the valve is leaking vacuum. This might affect idle.

[livemeyer]

I have an 85 720 (second owner and proud owner since 1989).  I blew up the engine (head gasket) in 2003.  I paid big bucks to have a shop rebuild it after my failed attempt left the piston frozen to a cylinder from sitting too long.  But this is just the beginning, not the end...

 

When I tried to build it myself I had bought a cam off of ebay.  It was a performance cam, with one of the biggest duration and lift available for the z24.  I have since forgotten what it was, possibly a Schneider?  I had the pistons honed ten thousandths over.  When the engine was put together I put a Weber 32/36 on it and a Pacesetter header. 

 

The truck is running almost EXACTLY how you describe yours to be running. It has a very rough idle.  When warm, it diesels when shutting off.  It requires a lot of advance, much more than stock.  It has very little low end power, but is a blast on the freeway because midrange power (2500-5000rpm) is good.  I would guess this engine puts out about 20hp over stock.  Still, I wish I could get it to idle better and not diesel.

 

Of note, I had to modify my distributor to get the timing right.  I imagine the cam sprocket is in the #2 hole, but should be advanced to the #3 hole, because what I had to do was shave open the distrubutor mount holes a little wider so the distributor could turn a few degrees more.  Either that or I need to try moving the cam on the timing chain by one tooth either direction. 

 

But before I do that, I'm going to check the basics: plugs, wires, cap, rotor.  I'm going to check where my vacuum advance is coming from, sounds like if I have it coming off manifold vacuum it will perform better.  I also need to check the egr valve for possible vacuum leaks.  Also, I'd love to hear what people's opinions are about the Outlaw 38 versus 32/36 DGEV.  I read on Redline Weber's website that the Outlaw 38 is the better choice for a highly modified z24.  If the only thing it does is improve idle it will be worth the investment.  If it improves idle AND boosts the bottom end then I will be very happy

 

- Dave

[datzenmike]

The weber needs an idle cut solenoid to prevent dieseling or run on. Just get used to stopping in gear and holding the brake. Lift the clutch pedal to load the motor as you turn the ignition off. This will stall it.

 

Idle will always get worse with more cam overlap.

 

Try the third and the first cam positions to see if retarding or advancing it helps. Retarding will add top end and advancing the other.

 

Check that both plugs are firing or it will act like it needs more advance. It should run well at 3 degrees.

[livemeyer]

I'm still trying to track down some issues...which have become more prevalent.  I have started to have timing issues, where I would get backfiring, mostly through the exhaust but occasionally through the carb.  Always, always, always in the past I have run my engine with a lot of advance.  Yes, it diesels, but at least it had power.  But in the past few months it stated to exhibit a dead spot in power delivery.  It would hiccup on a hill, sputter, sometimes die.  It would also get an occasional sputter in second or third gear with part throttle (WOT never a problem).

 

As a reminder, I'm running the Weber 32/36 on a rebuild Z24 with a "big" mystery grind cam.  So, I'm thinking carb or timing/tuning issues.  I replaced the power valve in the Weber.  I installed a fuel pressure gauge at the carb.   I installed the idle-cut solenoid that Weber sells. 

 

Next, I replaced the cap and rotor and the spark plug wires (I may replace the spark plugs themselves soon if I don't get to the bottom of this).

 

Tonight, I put the timing light on the exhaust #1 wire and surprised to see it at 0 degrees.  I put it on the #1 of the intake side and I don't see the timing mark come up at all.

 

One caveat: When I replaced the power valve, the C-clip that holds the choke mechanism to the choke butterfly decided to fly away.  I bought two more at Lowe's, the smallest I could find, one fell down when trying to get it on and the other flew off rather quickly as well.  Right now the truck is running horribly but I'm pretty sure most of its behavior can be attributed to the choke being disabled.  Still, I'm wondering if that has affected the timing I'm seeing, which at best appears to be 6-15 degrees off and at worst is much farther. 

 

I have a 38DGES waiting in the wings but I'm unsure if I want to swap the carbs over just yet.  If I have problems relating to some other part like the distributor or coils, swapping out the carb could make it even harder to figure the culprit.  On the other hand, it could be just the ticket...

[datsunaholic]

On the intake side, is it even firing?  Try #4 if it'll reach (will show the same place on the timing marks on the crank)

[datzenmike]

Double check your wires go to the correct plugs. You may have them mixed up which is easily done with eight of them.

 

The intake coil is powered from the ignition while the exhaust side is fused from the box. It matters not if the two coil wires are mixed, it happens but will run the same. Check and replace the first fuse on the far left hand side of the fuse box.

 

Advance is 3 degrees and while the Z engine will tolerate much more it doesn't produce as well.

Be sure both coils are firing. If the fuse is blown the engine will require more advance to run properly on only one coil.

Check the valve lash. 0.013" on all. A tight valve will cause backfiring.

[livemeyer]

Good info, all.  Thank you.

 

Update:  Today I installed the Weber 38DGES.  It was a fairly easy swap since the setup for the 32/36 was already in place.  Only change I had to make was to take the accelerator cable linkage off the 32/36 and put it on the 38.  The one supplied was set to have the cable pull from the opposite direction. Flipping it upside down would be the easy fix except it was too tall so I used the other one from the 32/36.  I had to cut an extra tab off of one side to make it fit but it was easy with the dremmel tool.

 

The new-style pins that come from the bottom and have locknuts on top to hold the baseplate for the air filter are really slick.  Used the battery drill with an 8mm socket and zip-zip-zip-zip that was done. 

 

So here's what I found: some plumbing hole at the top of the float bowl looks to have been a void and a vacuum leak on the 32/36.  On the 38 there is a nipple sticking out, looks just like the one for the fuel inlet.  Another possible leak may have been from the baseplate.  When I took the 32/36 off, I found the baseplate was loose.  There are two screws that use hex and are flush into the adapter plate.  Both were loose. 

 

What a shocker!  After getting the carb installed, the truck started fairly easily - took a while to get the gas in there, but once it was, it fired up and idled.  The shock was that is was idling at about 400 RPM!  it has never done that with this cam/engine before.  I suspect I killed whatever vacuum leaks I had because the idle was really smooth.  I made a few adjustments to get the idle at about 900rpm and went for a test drive.  Lots of power!  More bottom end.  Unfortunately I still find a dead spot, especially at half throttle from a stop or slow around a corner.  But with a good stab of the throttle the truck takes right off and acts like a horse that's just been kicked with spurs. 

 

I figure I still have some dialing-in to do with the tuning of the carb but at least it is running more predictably.  I used to have to stab the throttle when I was braking hard because the dive would cause a dip in idle and sometimes kill the engine.  It doesn't do that now, which is a relief and something I have to get used to (pleasantly). 

 

Now, about the timing:  After running the truck and going for a good drive, I put the gun on it again.  At idle the light firing with the #1 on the exhaust side was showing about 6 degrees BTDC.  #1 on intake side was not showing a mark at all.  I was able to turn my distributor to max and get to 10 degrees BTDC.  This is where I think this whole thing with the mystery cam grind comes in.  I think it is on the #2 mark but can't help but think that if it was correct on the #3 hole then the cam timing would be advanced enough that I could bring my timing back into the middle range instead of at it's limit.  What is odd is that I remember a time when I used to be able to get the timing advanced to the point where it would start to ping.  I can't help but wonder if somehow it jumped a tooth or something odd like that.  I'll have to share some photos, but for now just imagine that the normal set of travel is 0-100%, where it is set now is about 120%, and when it was at 3-6 degrees BTDC it was at about 80% of its travel. 

 

Nonetheless I am happy that it is back to running pretty well, if not perfect.  I have some other experiments to do and will update later.

[livemeyer]

If I ever just give up on this Z24 head and 8-plug ignition, which L-head is a direct or near-direct bolt on?  I'll need a new L-series intake manifold and distributor and coil as well, correct?

[ggzilla]

If only one plug is during, it needs about 10 degrees advance.

 

When both plugs are firing, it will have more power at 3 degrees

[datzenmike]

Cam timing has absolutely no connection to distributor timing. They are driven separately and adjusting one does not affect the other.

 

 

 

 

 

 

Double check your wires go to the correct plugs. You may have them mixed up which is easily done with eight of them.
 
The intake coil is powered from the ignition while the exhaust side is fused from the box. It matters not if the two coil wires are mixed, it happens but will run the same. Check and replace the first fuse on the far left hand side of the fuse box.
 
Advance is 3 degrees and while the Z engine will tolerate much more it doesn't produce as well.
Be sure both coils are firing. If the fuse is blown the engine will require more advance to run properly on only one coil.
Check the valve lash. 0.013" on all. A tight valve will cause backfiring.

 
 

 

Good info, all.  Thank you.

 
 
It is good info if you use it. Check for spark on both exhaust and intake sides. Most common is the fuse is blown. If and when you get both plugs firing the timing will be severely advanced and need to be around 3, +/- 2 degrees.

[livemeyer]

 

It is good info if you use it. Check for spark on both exhaust and intake sides. Most common is the fuse is blown. If and when you get both plugs firing the timing will be severely advanced and need to be around 3, +/- 2 degrees.

 

 

I do have spark firing on both intake and exhaust sides, as I had indicated earlier.  It is strange that the timing light doesn't show the mark when connected to #1 wire on the intake side.  It does show it on the exhaust side.  It is currently set to 10 degrees BTDC based on the timing light at idle on the exhaust side.  When I get a chance I will put the timing light across all 8 spark plug wires to make certain they are all firing.  I do occasionally get a non-reading on the intake side, meaning the light flashes steady most of the time but occasionally misses a pulse or two.  Perhaps the coil is weak?  It seems to fire most of the time and above idle the engine definitely runs smooth and isn't mis-firing. 

 

I have noticed the engine runs really well when advanced to that 10-degree mark.  It doesn't ping.  It does buck a little bit especially when getting on throttle after a 1-2 shift or a 2-3 shift.  I'm going to try putting it back to the 3 to 6 degree setting and see if I can get it to run as well there.  But make no mistake, to get these numbers I have to have my distributor turned almost all the way to the end of its travel.  I think this is compensating for something in the engine build or possibly another issue, but I don't know what. 

 

I read up on some other posts about grafting an L-head onto the Z block.  It looks too complicated to me, a Frankenstein motor I'm not wiling to do.  If I was going to go that route I'd rather just put a complete L motor in it. 

 

Regarding cam timing versus distributor timing, I understand what you are saying, but there is a relationship there.  The distributor has to be "in time" with the engine (including valvetrain) in order for the engine to fire correctly and run smoothly.  For the longest time I felt (and still kinda do) that the mystery cam I have may have been a faulty grind.  I had trouble getting the cam gear to mount to the cam when I was working on it (10 years ago) and when I had a shop do it they gave it back to me with the caveat, "it is rebuilt and it is running, but we set it to factory tune and it has little power."  Only bringing the distributor up way in advance did the engine sort itself out.  Because it is a mystery grind I have always wondered if it needed to sit into the #1 or #3 hole in the cam gear.  That +/- 5 degrees could make a big difference on where the distributor needs to be set.  But this is all just postulation on my part, I really just am trying to take the best advice here, experiment with different settings to get the engine to run its best.  Currently, with the 38, it has even more power than before, but it looks like I still have some work to do to figure out the right tune for the carb and best operational timing for the engine.

[datzenmike]

I would recheck the plug wires. Both coils fire the intake and exhaust together, so the timing light should show the same on both wires. If not then find out why. Could one side be jumping to ground? There are 8 plug wires and two coil wires jammed onto a cap and two rotors.

 

Spark timing should fit the location of the piston more than valve timing. The spark has to light the fire far enough in advance to reach maximum cylinder pressure at about 15-17 degrees after TDC in order to push the downward accelerating piston with maximum effort. Too soon is wasted and too late the piston has sped up and it is chasing it. 

 

Valve timing on the Z24 is set on the #2 hole but you can go to the #1 hole to advance the engine to favor high RPM power or to the #3 hole to improve bottom end. (can't have them both, although #2 is a compromise)

[livemeyer]

Datzenmike you were absolutely right.  I don't know how, but some how 3E and 1I got mixed up.  This happened a long time ago, not with the recent cap and rotor and wires I replaced.  This recent time I was being very careful that I did one wire at a time and didn't cross any up, never suspecting that I already had two mixed up.  After I found that i took it for a test drive and the stutter at a rolling slow in second gear stopped!  And I had to chuckle, because as soon as I solved it, it was suddenly obvious, as the crossed wires would of course cause al the weird issues I was having, including occasional backfires out the carb and the exhaust, no timing light results on the intake side and poor idle. 

 

So, right now the engine is running the best it ever has.  I have the time set to about 6 degees BTDC and the Weber 38 cured all the rough idle issues.  I noticed my current tank of gas got sucked down super quick, but most of that can be attributed to putting my foot into it since the truck didn't like anything under 2000 rpm when the two wires were crossed up.  I now have my idle set around 900-1000 rpm and if I can stay under 75 on the freeway (it is a lot faster!) then my mileage should improve a bit.  

 

I drove it to Seattle and then Bellevue today, it had rained in Seattle and when I "got on it" in second gear the tires broke loose in the wet.  Just a reminder that this truck is really light and will need a light touch when the weather is less than perfect.