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Thanks again! I reached out to zKars, I’ll see what he has to say. Also, I wonder how much I could mail off the E31 cylinder head to help get the compression ratio back up before I ran into chain tensioner issues?

Hi, I'm sure the compression on a L20 with a E31 head will be misarable.. you need the e30 head. As i once put a E30 on a 240z 2393cc engine it made far to much compression it needed a really FAT headgasket.. I've got 2! E30 heads in my pile of parts, one complete rebuild and one still in parts.. but they are expensive i have heard.. Also i'm in the Netherlands, Europe. I think one day they will find theire way to Japan... 😀

My vote is that electronic distributer. Do you have an old points style one you could swap back to ?

I'd see if you can work out a deal for the proper head if you're looking to be close to a restoration. I don't want to hurt zKars' position but he did say "never been able to sell". Seems like he's been waiting for you... Good luck. I redid the math for what should be the E31 head and got 7.7. Didn't add your millimeter overbore though. Also found that some of the engine calculators out on the internet seem to have the wrong chamber volumes. I used the dimensions and reported CR from the FSM to calculate volume. Just for fun.

It’s a very low number, numbers matching, right hand drive car.

Is there a specific reason that you're trying to save the L20?

I appreciate the response, also I would be taking the block 1mm over to 79mm for the pistons above. I used a few different calculators and was getting in the mid to high 7’s and that’s what made me worried as well as potential valve clearance issues with the block using the E31 with the larger valves. I saw that Tony D had mentioned using L24 pistons in the L20 block but I’m guessing it would have to be sleeved? I think that would be my best way out if the block doesn’t need sleeved.

Hi all! Currently restoring the rear hatch in all its glory, and dug through this thread. Does anyone know if the outer gasket/foam seal on the interior hatch panel (the one with the rubber flaps for rain, etc) is the same soft 8mm foam as is used on the vent shown here? Looking to replace the degraded foam, and trying to figure out the correct material. Cheers! IMG_6962.HEIC IMG_6965.HEIC IMG_6971.HEIC IMG_6976.HEIC

I got 7.5 for the CR of an L24 head on an L20 block, assuming the L24 head is the dual SU head. Probably want to get with zKars on that L20 head. Realized that I used the E88 L24 head for the calculations. 8.6 CR instead of 9.0. I'll redo them later. Probably still under 8 CR.

Maybe try one of these cheap plug testers. At least you could visibly see spark getting to the plug and rule out ignition. What do the plugs look like? https://www.harborfreight.com/90-in-line-spark-checker-63593.html?hftm_sc=532&hftm_source=google&utm_source=google&utm_medium=cpc&utm_campaign=21901271210&campaignid=21901271210&utm_content=171677806542&adsetid=171677806542&product=63593&gad_source=1&gad_campaignid=21901271210&gbraid=0AAAAADAHb4cCWCcSJ4qCMytUVmlv7v7bX&gclid=CjwKCAiAlMHIBhAcEiwAZhZBUlzpLzH9TR7YSC9i3f7bzmYEm7gw-Ai3uRRfne-Qjhh-zYy0O4G-khoCpwwQAvD_BwE

Disconnect at the manifold/header exit and run your borescope up that way. That distributor looks like just a magnetic pickup distributor, that uses an external ignition module. But your exhaust blockage sounds reasonable. Good luck. Post pictures.

Your compression test would seem to rule out anything mechanical in cylinders one and two. And yes, front carb supplies all three front cylinders, so I would not suspect a "no fuel" issue. How confident are you that the carbs idle settings for the carbs are where they should be - so both carbs flow the same amount at idle? And, when revving? Spark plugs can be dead right out of the box. I'd move plugs around and move plug leads around with them. I'd try swapping known good, perhaps from six to one and from four to two and vice versa. I think a Z engine will have a very hard time running if it has two totally dead cylinders. They may be intermittently firing a bit. So, new plug wires, new plugs, and new distributor cap?

I have had bad spark plugs before...brand new ones. Ended up cleaning an old one and sticking that back in.

Distributor I'm running Cody thinks the car starts on all six and then starts misfiring. An exhaust obstruction might do that... eBayNew L6 Electronic Distributor Replace For 1970-1983 Datsu...1970-1983 Nissan Datsun 240z 260z 280z. Product Type: Electronic Distributor. 1 x Electronic Distributor as Picture. (The Compatibility Is Just For Reference. -Will dramatically improve the sporty app

More info: Pulled the float bowl lids, fuel was within 0.10" of the same level in both bowls. Pulled the front carb. No obstructions as far as I could see with my ancient borescope. Clear into the head but couldn't see the valve stem. Took the valve cover off and all valve actuate as they should appear to have the proper lift and return. No wiped out lobes Reassembled it all and tried it again. #1 & #2 are both dead. #4-#6 are over 100dF within 15 seconds. The front two are 80dF. Rev it up and hold it for a short while and no change... Next weekend the exhaust will come off and we will look for FOD... Hopefully I can get it apart. The exhaust paste I used is pretty tenacious and I haven't found anything that will dissolve it yet

Probably not your issue, but thought I would share. I had an issue with my white Z where it ran great driving to a show 20 miles away and then horribly on the return drive. Cylinders 2 and 3 were bad. I was convinced it was fuel and wasted a couple hours rebuilding and then replacing the front float bowl shut off valve. Eventually I took off the valve cover and saw that the #2 and #3 valve rocker arms had 'relocated'. The end that was supposed to depress the intake valves was no longer touching the valve. Long story short, took the head to the machine shop and was told the valve stems were all gummed up from running old/bad gas. Sadly, I do not drive the cars enough. Anyway, put it all back together and it runs great now. Machine shop cleaned all the valves and guides. Fortunately, no damage was caused to anything except for my wallet. You can see the two valve 'nicks' on cylinders 2 and 3 in the pic.

I ruined a GM HEI module by running the engine with two spark plugs disconnected. I assume that a stray high voltage discharge, or some sort of "flyback" (it's a thing), made its way through the module. After I turned the engine off and reconnected the wires the engine wouldn't start. I checked spark and got a weak orange spark. The engine would start with starting fluid but would not without. Put a spare new module in and it fired right up. How about some details, just for fun, on the new electronic? Is it a ZX type or Pertronix or something else?

Plugs are new numbered Nissan. Don't suspect them... Distributor is new electronic from Ebay. No resistor. The cap doesn't locate very positively. So being made in China makes it a suspect...

I'm still trying to figure out what caused this kind of damage 🤔

I've also seen old plug wires crossfire or short to ground. Waaayyy back in high school working with old worn out car parts. Used to have to arrange the wires to avoid problems. Also seen that visible weak spark does not always spark under cylinder pressures. Had a weak ignition module once. You're probably running points though?

Correct firing order? 1-5-3-6-2-4 CCW?

You can back out combustion chamber volume using compression ratio and displacement. The 1972 FSM has the numbers. And if you have the head and block in hand you can take some measurements.

How about the old standard of mixed up firing order? Just watched a pro do that. It happens.

Do they have good grounds? Have you tried to bench test them?

New quandary. Need some help! The car is not running on all six cylinders. Using an IR gun the rear 4 are fine over 200dF in just a short period of time. #1 is cooler in the 150dF range and #2 is cold at about 90dF. So we ran a compression test this afternoon. All of them in the low 180#'s except #6 is 178#. So we ruled out valves or stuck rings?? With a timing light I checked all six yesterday and the light strobed on all 6 cylinders. So the plugs are firing?? We moved the plug wire from #2 <-> #3. Same problem and plug #2 was pretty clean... It seems to me if we had a fueling issue then #1-3 would all have issues?? So grasping at straws: An obstruction in the intake manifold or exhaust header? #2 isn't actually sparking? Some problem in the distributor cap? There is not enough fuel in the front intake manifold and #4 just takes it all?? Don't have the patience for this... :(