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Syn's 1972 240z


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Warmed up the car to operating temp and performed another leak down test. Each cylinder was less than 5% leakage which is showing that the compression rings are good at least. I'm still torn whether or not it may be the valve seals or oil rings. I did not put the valve seals on so I don't know for sure if they are correct but my friend/mechanic did them so I trust that they are. When the car was warming up, there was no smoke coming out of the exhaust until about the 4ish minute mark where I could start to see a little bit of smoke but nothing substantial. Seems to only smoke when warmed up and driving around but at idle there is hardly anything.

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Quick little update. Took the motor back out as it was either going to be the valve seals or rings so figured this was the easiest. Also going to be putting in a 5 speed so will install both engine and tranny together when that comes. Anyways, I was looking in the exhaust chambers to see how much oil there was in there when i noticed that the intake valves had oil sitting on top of them which leads me to believe the valve seals are faulty. Ordered a set of those today and will hopefully get them sometime this week and have everything put together by the weekend. 

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Bad or missing oil seals tend to start up with a big puff of smoke from oil that ran down the guide after the last shut down. Intakes are under intake vacuum but exhaust are somewhat pressurized when running. Both will leak when engine is off.


Is this an automatic right now?? I checked but may have missed it.


Is the oil overfilled?


What oil are you running?







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It doesn't smoke right away on startup. Take about 3-5 minutes or there abouts. It is currently the original 4 speed in it, just wanting a 5th gear which is why I'm wanting to swap it. I made sure to not overfill the oil and checked the dipstick multiple times to ensure that. I was using Joe Gibbs Driven 5w30 break in oil as that was what was recommended to me to be the best stuff around.

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  • 4 weeks later...

Update Time


Tore it all down again to double check everything, look over the rings and replaced the valve stem seals just in case. Nothing out of the ordinary. Put the 5 speed in while I was at it. Assembled it all together and took it for a small drive. Still smokes. Everything appears to be within spec but I have no idea why it is still smoking. I'm about ready to just put the original engine back in it at this point and I don't know what else to check...

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Time for another update. Took the entire exhaust system off except for the headers to see if maybe the residual oil in the exhaust was part of the culprit or not. No smoke comes out of just the headers unless you drive it around the neighborhood to warm it up. Doesn't hardly smoke on idle but if you give it gas, it does smoke. Reading other forums throughout the internet has me wondering if this cam could be part of the problem as I'm told it creates a decent amount more vacuum which could be pulling oil through the valve guide seals even though I have put 2 new sets on already. Is that something plausible with these engines? If so, is there a different valve guide seal kit I can order that would prevent this or minimize it?

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  • 2 weeks later...

Valve guide seal update!

So, I replaced the valve guide seals again but this time found out from the dark corners of the interwebs that valve guide seals from a Ford 2.8(?)L engine fit for our Inline engines. Pick up a set of those from Amazon for about $22. Part # Fel-Pro SS 72686. These fit snuggly and have solved 90% of my smoking problem. Now that oil isnt being burned, found the other 10% of my smoke to be unburned fuel. Poked around and found out my vacuum advance is not working. Is there someone that sells that part? I've checked rock auto, zcardepot, and a few other places but can't seem to find anyone that sells just that part. Was thinking it would be a simple part to find but I was wrong.

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Was able to clean up the inside of the distributor and got the vacuum advance working again. Just some crud in there getting in the way thankfully.

Looking to tune the carbs since the car is running so rich and noticed the idle mixture screw on the dual webers was screwed in nearly the entire way and its still super rich.

What is a baseline for jetting an L28 engine so that I have something to go off of? I'm at roughly 3200 ft above sea level. I will be taking the top of the carbs off either tomorrow or the next day to see what jets are currently in it.

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Weber 32/36 DGV 5A Carb Update

Took the top off both of the Webers to see what jetting I have.

Fuel: 140 Main 135 Secondary

Main Emulsion Tube F50

Secondary Emulsion Tube F6

Accel Pump Jet: 5C

Air: 165 Main 160 Secondary


Oh, and I found the rear carb to have a loose power valve so I'm sure that wasnt helping anything.


I'll be digging around the internet to get an idea what I should have in there or if anyone here is running something similar that I could use as a base tune, that would be appreciated.



Using this website (http://www.carburetion.com/diags/3236DGVDiaginfo.asp) it appears that I have stock jetting for the Webers.

Edited by Synestran
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Neighbor let me borrow his Gas Analyzer after putting the carb back together after finding that loose power valve.

The first image is of it running at idle at operating temp and this was the best I could get it with the mixture screw turned in nearly all the way. So, its definitely still running rich with the stock jets in it. Doesn't really smoke at idle doing this.




This next image shows it running with 2000 rpms in idle hydrocarbons dropped some which is good but the AFR didn't really go up much. Was told I should be looking for high 13's and HC count of around 400-600ish? It is smoking with higher revs while doing this. Not quite James Bond smokescreen but a steady cloud and smells of gas too.



Anyone have recommendations for jetting after seeing these numbers?

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  • 2 weeks later...

Carb Update:


Ordered some new jets so now my Idle Jets are 50 Main and 45 Secondary. Fuel is now 135 Main and 130 Secondary. Using the Gas Analyzer, I was able to read an increase to about 14.05 AFR at idle so getting closer to the goal of about 14.7 if I can. Ordered 2 more jets to put the idle jets at 45 Main and 40 Secondary which should be able to put me right where I want to be for AFR. Hoping to get those by Thursday or Friday this week. Exhaust smells more normal already and less like fuel so I feel I'm finally getting this buttoned up and dialed in.

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Hey guys,

Driving the Z around a little bit here and there since the weather has been nice. I've noticed that the last 2 days it has a poof of smoke upon start up like worn out valve guide seals. Considering this is the 3rd set I've tried, would it be possible that the smoke could be coming from the valve guides themselves if those are shot? I took the head to the machine shop to have it looked over and I don't remember him saying anything bad about the valve guides. I'm starting to think that is what is causing some of this smoke as I'm still losing oil and it's not on the garage floor.

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  • 1 year later...

Gave up on this build for a little while as I was frustrated with it and had other things going on anyways.

Found oil pooled on top of the closed exhaust valves which had me thinking it was valve stem seals still (just had the valve guides replaced a few months ago). Bought a new set and swapped those out hoping to finally figure out if that was causing the smoke issue. Still smokes and fouls out plugs incredibly quick.



Took the head off to look at the walls, cylinder 1 and 5 each have a spot where you can feel an imperfection and all cylinders have a vertical striping going on. Someone else assembled the engine so who knows if he even saw these spots or not. Will be taking it to a machine shop to see if I can bore it out to get rid of these spots.


Edited by Synestran
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