I have a 240z and I recently put an l28 in and replaced the fuel injection for carbs. I have everything hooked up, and I got a new fuel filter and I got a new mechanical fuel pump, but when i start the car I am not able to start it. When I spray gas into the carbs and suck up some fuel through the fuel line I am able to start it for like 3 seconds but I am not seeing any gas come up through the fuel filter. What should I do at this point? Could there be a problem with something in the engine that is preventing the pump to work? does the l24 have something that an l28 doesn't have that allows it to use the mechanical pump instead of an electrical? Any help would be much appreciated.

also I was wondering if u are able to crank the engine while the valve cover is off. I want to see the inner workings so I can see if the fuel pump arm is being pumped.

Disconnect the fuel pump output and run a hose from it into a coffee can. Turn the engine a couple of times to see if the fuel is coming from the pump. If not then you might have an obstruction in the fuel line and need to blow it out.

Yes, you can start the engine with the valve cover off, but be prepared to do a clean-up job. Have you taken the line loose from the fuel pump to the carbs while cranking to see if you're getting fuel flow?

well the thing is I don't think there is an obstruction because I set up a clear hose at the end of the fuel line and was able to suck gas through it with no problem.

Sucking ain't the same as pushing. If you wire your horn up backwards, does it suck or blow?

Sucking doesn't tell you that the pump is working.

I haven't taken the line loose from the fuel pump to the carbs, but I assume there is no fuel flow because the fuel filter is clear an I would be able to see it going through there if there was any fuel flow. When I sucked fuel up orally I saw going through the filter but nothing when cranking it.

well if the pump isn't pumping its not a problem with the pump cause I just bought it brand new.

There are 2 things involved in starting a car, fuel/air and appropriately timed spark. You have half of that equation, since it starts with a gas splash.

You need to eliminate the fuel issue by verifying you have fuel delivery to the carbs. If you do then you may have a significant vacuum leak that's preventing normal start/run.

Yeah I got the thing started finally. turns out the l28 didn't have this oval shaped thing on the inside of the valve cover to pump the mechanical pump. I took it off from the old l24 that was all seized up and put it on the l28 so the fuel pump actually started to pump. The car is out of tune and sounds like and old WWI airplane engine but the thing runs pretty smoothly.