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When I run my adjusters all the way down, I have LOTS of clearance. Like almost enough to actually pull the rocker out without even compressing the valve spring. Almost, but not quite. Point is... Something really doesn't seem right. I bet I could install the thickest lash pad ever created and STILL have clearance when my adjuster is run all the way down. Are you double dog sure that everything else is as expected? Valve stem lengths are correct? Valve seat depth is as expected? Head not cut on the top side to clean it up? Something? And about the carb float valves... I think they switched to the rubber tipped valves in 1972 "improving sealing performance".

Yeah, something really isn't right. I have snapped a bunch of pictures and talked with my engine builder, who did the work on this head. The current hypothesis is that the SI Stainless valves I bought are too long. The installed heights are still visible in black marker on the cyl. head: 1.787" is a lot more than the specification paperwork from Iskenderian (1.700"): The lash cap I pulled out with the one rocker arm I removed last night is .117" and about 3 tenths. Stock is .118". But the "kit" I ordered from Iskenderian has .175" lash pads, (part LC175 - is .175" thick - I looked it up on their site): The retainers currently installed look like the Isky ones. The depth to accommodate the lash pad is notable. Comparing to another exhaust valve which has not had the rocker and lash pad removed, the lash pad (I am assuming also .118"/stock) is "buried" in the retainer. So, the theory right now is that SI Stainless valves are taller than the stock valves (4.620"). I think I will have to pull the head. My engine builder is a great guy and he has provided me with so much value over the years. In this instance, I should have checked the wipe pattern before installed the head, but I did not. As far as I can tell, no damage has been done. So, I think I have been fortunate here.

It's cheaper to try a new ignition system!

Lets not forget this is a California Datsun engine! That's probably the root of the problems! After these years, I would have just purchased another engine with the stock cam and not messed up by a builder that doesn't know what they're doing.

You could try one. It would not hurt anything. I had one on a 2 cycle dirt bike that would foul the plug when I didn't keep the RPMs up high enough.

From past experience with what you are dealing with is the 3:90 ratio the engine will run at 3k rpm on the highway between 60&65 mph. 3:73 is probably optimal if you want to bring it down a bit. Although getting to that speed the 3:90 gets you there quickly.

Automatics were 3:54 with the 4 speed being 3:36 Most 5 speeds had the 3:90 but in a R200 diff. Other ratios are available as well.

This evening, I examined the needle and seat from the rear carburetor. If found some residue on needle. When I used a wire brush to clean it up and examined the needle (it is metal) closely, I could see a light wear ring. I found two spares I have had for decades and examined them. The needle portion appears to be made out of a hard rubber. I may have bought them new to swap out in my carbs that I used to run on my track car, but never did. Can't remember now. Anyway, they looked pretty much like they were unused. So, I swapped those into the front and rear carbs and reset the float levels using the "wet method". By siting the fuel in a clear tube, they are both set perfectly now. After that, disengaged the balance screw, and set each carb throttle adjusting screw so that I saw the lever move. I set each at about 2 turns in. Then, I turned the key and the engine came to life. Within a couple of minutes, I had the front and rear carbs running on just the carburetor throttle adjusting screws. I turned in the auxiliary shaft adjusting screw to operate the linkage and then adjusted the balance screw to get the air flow the same between the carbs. At that point, I was going check the timing and start adjusting idle speed, but the clatter from the valves was too much and I began to be concerned. So, I decided to shut it off and pull the valve cover. Upon doing so, I was pleased to see no obvious damage to the cam lobes (I had a couple of bad experiences with new cams in my track car). I started checking valve clearances. Just about every one of them did not have enough clearance. I went through and made minor adjustments until - you know it... the last one. For that one, I ran the 14 mm adjustment screw all the way down, but I ran out of adjustment and still couldn't get a .20 mm feeler gauge (it is an intake valve) in between the cam base circle and the rocker pad. So, I pulled the rocker and lash pad. The wipe pattern is not centered and nearly off the front edge. Guess who is going to have to pull all the rockers and potentially change out some lash pads?

Hahaha - you guys got me laughing. And good advice, I didn't even think about using water - because everything is new and done right, right? Wrong! Dang water pump. Anyway, I just got in from the garage. I finished my to do list. I did the thing with pulling the oil pump and using a dummy shaft and a drill to pump the oil through the engine. I hate the part where you have to remove the oil pump again and reinstall the distributor drive shaft. I made a big oily mess. But, the engine has been sitting for years after being rebuilt, so I feel better pushing oil through it before cranking it. I didn't want to spin the engine with the starter as long as it take for the oil pressure gauge needle to show pressure without pumping oil everywhere first. After that, I pulled the spark plugs and switched on the starter. I kept it spinning until I saw the oil gauge needle just move a bit. It is amazing how long that can take. I didn't time it, but I bet the starter was engaged for 30+ seconds. After that, I put the spark plugs in, hooked up the leads, looked at the engine bay for about 10 seconds trying to think of anything I had missed for the 30th time today, and then thought "f*** it, let's go". I lifted up each carburetor piston and shot some starter fluid in the direction of the intake. And then I turned the key. I got a bit of life from the engine within a couple of cranks, but when I let the key go it would die. I tried that a couple more times and got the same result. Having a good amount of experience with these carbs, the symptom seemed to be that the two carbs were way out of balance. I operated the main linkage and looked at the resulting movement at each carb linkage. The rear carb linkage was activating, but the front carb linkage was not. I adjusted the screws to get them both moving when I threaded in the main throttle screw. Then I tried again. This time I used the starter cable. It fired up, but having fresh in my mind what @siteunseen had said, I treated the ignition keys like a feather trigger, and when the engine revved up pretty high, I turned it off. I pushed the starters in a bit and tried again. This time it fired up and was holding revs at about 2400. Oil pressure was showing 90 psi (I assume the sender I bought must be the one for the early cars?) Not pausing a second, I swung around from behind the dash to the engine bay and bounced my gaze around to check on key things. Almost immediately I noticed fuel flowing up and out of the air vent in the top of the rear carburetor. So, I shut it down. I am not sure what happened there. I set the float levels just a few days ago. Perhaps I have a bad needle/seat. Total run time was only about 30 seconds or so. I was really hoping to run it for about 20 minutes at 2000, as the cam is new and the rockers have been reground. Really hoping that everything got lubricated enough quickly to avoid any problems. I will need to see what is up with the rear carb and try again.

Brigham City, Utah, Sept. 7, 2024 - 1,070 cars. I found I had relatives/in-laws with Z's, we were the only Z's except for a 370Z that was with the tuner cars. The ZX is an original turbo car and the 280Z has a LS under the hood. Different generations, we had a blast and I'm old enough to be their grampa. Funny, one kid about 12-13 walks by and says "look, Jaguars".