so i just picked up a 71 240z. engine is a stock l24 with e31 head. only modification is a flamethrower ignition . car was running rough probably about 60-70% of its capabilities.  so previous owner parked it and was sitting for about a year. i replaced the mechanical fuel pump , installed new spark plugs, wires , distributor cap and still runs exactly the same. i had to blow air through the return line in the fuel system to get it running so the fuel filter would actually fill up to keep the engine running. to me it seems like the carburetors aren’t getting enough fuel. i was thinking of either rebuilding them myself or ordering new ones from ztherapy, but i don’t want to do that (mainly ordering new ones) if it’s not the issue. so i was wondering if someone could help me out in trying to diagnose it instead of just throwing a ton of money at it. 

i also noticed the carb damper oil was real low if any at all so i filled that up. 

Edited September 28, 20204 yr by rosaaen89

It is possible that the carbs need to have their float levels adjusted.

Do you have an airflow meter to ensure the carbs are sycned up together?

What do the spark plugs look like?

i don’t have an airflow meter at the moment. when i pulled the spark plugs the front 3 were light tan/ whitish and the back 3 were black with carbon built up on them 

the mixture is off ! floats need to be set or checked , start with the mixture screws turned down 2 1/2 turns and then balance with a air flow meter. you can try leaning the back carb with turning the mixture screw up but you will still need a air flow meter to balance. a member here sells the float- sync for the carbs  on ebay which I bought and is the best tool for the float adjustment I have ever used . set the floats first then the mixture and last balance . there is also a color tune for setting the mixture also which you can buy online.

i will probably order the float sync , i was thinking about taking it to a local mechanic but i’m in the middle of nowhere in new mexico so i doubt they know much either. if the mixture is off/floats not correct though would that keep it from running ? or just make it run really poor ? 

8 hours ago, rosaaen89 said:

i don’t have an airflow meter at the moment. when i pulled the spark plugs the front 3 were light tan/ whitish and the back 3 were black with carbon built up on them 

Before you decide to open up the carbs you may want to check for leaks around the balance tube, intake manifolds, and the carbs by spraying carb cleaner/starting fluid around them. Listen for idle changes of a warm engine. 
I just spent weeks looking for a lean idle on my back carb until I found a missing cap on the side of the carb. When I called Ztherapy (purchased in 2001) Steve Explained that a back fire can cause the butterfly shaft seal to blow out. But,
Any kind of a leak will cause idle and run issues. Cheap and easy check to do.

if you don’t find anything there then go back to basics. Reset mixture at 2 1/2 turn  (note what they were set at) and see if it will start and idle. Disconnect choke gables. Check that the nozzles are returning all of the way. 

Don’t give up. Lots of great help here. 

11 minutes ago, 7tooZ said:

Before you decide to open up the carbs you may want to check for leaks around the balance tube, intake manifolds, and the carbs by spraying carb cleaner/starting fluid around them. Listen for idle changes of a warm engine. 
I just spent weeks looking for a lean idle on my back carb until I found a missing cap on the side of the carb. When I called Ztherapy (purchased in 2001) Steve Explained that a back fire can cause the butterfly shaft seal to blow out. But,
Any kind of a leak will cause idle and run issues. Cheap and easy check to do.

if you don’t find anything there then go back to basics. Reset mixture at 2 1/2 turn  (note what they were set at) and see if it will start and idle. Disconnect choke gables. Check that the nozzles are returning all of the way. 

Don’t give up. Lots of great help here. 

i’m going to double check all the fuel hoses and carb hoses . thing is the car will start but i have to prime it by blowing the rubber hose off the return line with air so the fuel filter fills up then starting it. sometimes it’ll die once that fuels gone or it’ll actually keep pressure and run/idle for as long as i want it until it sits for a day or two

  check the fuel filter, its a cheap change if the car has been sitting for a long time , might not be getting enough fuel through it. check fuel pump , is it mechanical or been change over to electric? start with the basics make sure you are getting enough fuel first, set carbs to 2-1/2 turns down, see if it starts and runs. if still hard starting your floats might be set to high leaving not enough fuel in the carb bowls.

i replaced fuel filter it’s a clear one. fuel pump is new and it’s mechanical . i just now removed the cables for the choke. when i move by hand the nozzle on the bottom of front carb moves down and up some but the nozzle on the rear carb when moving the choke by hand doesn’t move up and down at all. Also i think one of the clamps that holds the small hose running from the nozzle to the bowl might’ve had a pin hole in it from being old and brittle but not sure if it happened when i removed it.

Edited September 28, 20204 yr by rosaaen89

5 hours ago, rosaaen89 said:

      thing is the car will start but i have to prime it by blowing the rubber hose off the return line with air so the fuel filter fills up then starting it. sometimes it’ll die once that fuels gone or it’ll actually keep pressure and run/idle for as long as i want it until it sits for a day or two

Sounds like you are pushing the fuel in the fuel rail back into the filter. My experience is that a mechanical pump doesn’t fill a stock filter completely 

if the choke is not moving nozzle that may make it harder to start when cold  it shouldn’t affect the warm idle or drive ability.

is the hose leaking at all?

 

Edited September 28, 20204 yr by 7tooZ

yeah i push it back into the filter so i can get it started. once i do that sometimes it’ll continue to run and idle,  other times it’ll die. i haven’t noticed any fuel leaks, but there is stronger fuel scents than there should be. i moved the nozzle manually by the lever itself without choke cables attached and they’ll now both move up and down. if u move the nozzles all the way down they get stuck. 

Next time it dies take the hose off the bottom or "in" of the filter. Blow back to the tank with your lungs. If it's hard to do at first then gets easier, and you might also hear some bubbling noise from the tank, my guess would be a crudded up gas tank. Your problem and attempts to fix are exactly like mine when I bought a '72 that would only run long enough for me to get away from my house and then walk home to get help towing it back. Then I tried the blowing back trick to clear the gunk out. That would let it run long enough to get home.

Here's what came out and a shot with a borescope. It wasn't rust just years of rotten gas that turned to varnish. Goodluck, I hope you figure it out. Cliff