There are still three fuel rails, one from the filter to the carb bowls. The second one sends excess fuel back to the tank. Nothing to and from the third hard line. I installed a push button switch so I can force the electric fuel pump on. The mechanical pump has been removed and bypassed. While setting float levels I would hold the button down for about 10 seconds while the bows fill, I could also hear gas trickle back into the tank. I have z therapy site glasses on the carbs and when I try to start the engine, the fuel levels in the bowls does not go down, or it doesn't look like it. Is it possible too much fuel is being sent back to the tank?

One more thing you should look at as a possible weak link.

The hose that goes from the float chamber to the nozzle has to be soft.

Off the shelf 3/16 fuel line doesn't work too good.

Another thing on the no start is the linkage has to be just right between the carbs. Those flat stops can look right but be out of order.

@Captain Obvious do you know if the fuel rail for flat tops work with earlier carbs?

The fuel lines to the nozzles are kind of stiff. They are a plastic material I bought from a hobby shop, made for model airplane fuel. I bought some su rebuild kits, came with new rubber tube's, did not install them.

I made the assumption the fuel rails were the same from flat tops to round tops. I'm wondering if I should pinch off the line returning gas to the tank.

The electric fuel pump doesn't get electricity until the engine runs, until the engine runs, residual fuel in the bowls is used to start the car, it works that way on my 72 240z.

I believe I swapped out the entire intake manifold, not just the carbs. So the linkages were from a 240z, but we know what assume does. I th8nk the choke linkage may be stiff too.

That stiff choke could be the hoses on the nozzles. From what I've learned the choke is actually just dropping the nozzles, no closing of the butterflies like most chokes. I bought one a few years ago somebody had put stiff fuel line from float chambers to the nozzles. It was so hard to pull the lever back I broke where the pull handle connects under the console. Lucky for me they make a better bracket that mounts to the sheet metal tunel.

Z Car Depot Inc

Choke Lever Mounting Plate Reinforcement 240Z

Choke Lever Mounting Plate Reinforcement 240Z - 800-733 (). Choke and console reinforcement plate for use on Datsun 240Z 1972 to 1973 that use the series 2 console where the choke lever was shifted to

And I would try clamping off the return and see what that does. At worst the fuel will come out the overflow bungs on the lids. I've seen people run the overflow hoses into a empty drink bottle or a big medicine bottle to keep fuel off your engine.

I apologize if I'm confusing your work. I just read the forum a lot and throw stuff out hoping it could help the problem. Cliff

I'm the original owner of a 72 240z, it's on blocks now, I want to get the 260 out of my hair so I can get back to restoring the 240.

I'm all ears, been working on cars for a long time but I've forgotten a lot of stuff, I listen to everyone's suggestions. I've known for a long time the hoses can't be too stiff and normal fuel line is too stiff, that's why I used the special plastic tubing made for model air planes, but as it got older, it got more stuff. I have some chores today, when I get back I'll look into the choke linkage and hoses. BTW, the choke lever broke many years ago and was replaced then, it is a weak point, ever since then I would never pull the lever by the end, always at the base of the lever, couldn't believe how much those levers are selling for.

I need to step back and look over the mechanism.

Keep up the suggestions - Jim

The flat top fuel rail should be perfectly fine to use with round tops. It has a restrictor orifice in the return line just like the rail used with the round tops. Other than the relocation of the outlet nipples that lead to the carbs, they are interchangeable.

7 hours ago, emptech said:

I have z therapy site glasses on the carbs and when I try to start the engine, the fuel levels in the bowls does not go down, or it doesn't look like it.

The engine uses a small amount of fuel at idle. In fact, if the carbs are tuned properly, the engine should idle for about 30 seconds or so just consuming what is in the bowls. No fuel pump supplying fuel necessary. So you should be fine running off the bowls until the pump turns on. It'll run for a surprisingly long time.

First thing I'd do is look for vacuum leaks. A hose you forgot to connect, or a nipple you forgot to block off?

If no joy there and you're double dog sure you have no vacuum leaks, I'd drain the bowls (disconnect the tube on the bottom and let the fuel run into a cup) and then refill the carbs with known good fuel. You can easily do that by disconnecting the inlet fuel line and sticking a small funnel into the hose. Pour fresh fuel in from a little cup until the carbs won't take any more. At that point, your bowl levels should be good and you should have 30 seconds of fresh fuel.

Maybe disconnect the fuel pump so it doesn't push any more questionable fuel back into the carbs.