1972 240z Stalling after a few minutes of driving.

[Captain_Zeros]

Please correct me if I'm wrong, but don't SUs get richer as float bowl fuel levels drop? As fuel levels drop, the surface of fuel in the jet moves downwards to a narrower portion of the needle and actually uncovers more surface area for engine vacuum to draw on?

[cbaker]

Same thing on 2 of my 240's. It sounds like vapour lock...fuel boiling in the rails that run along side of the valve cover. Remove them and insulate them. Also remove the manifold heating where the glycol runs through. I thought mine was ignition since it feels like it but it's not. Common on the 240's since it gets hot under the hood.

[Mark Maras]

Sus get leaner as the fuel level drops. The fuel level is supposed to be just a little below the top of the jet which is determined by the float level. Easy to test the vapor lock theory, test drive it with the hood cracked open. My previous 71 Z & I shared 20+ years as a DD & despite not having insulated f. lines, only a heat shield, I didn't experience V. lock once.

[mckennar]

Howdy all,

Update: with ambient temps at 56f at 4:30 this morning, I drove it with a trail vehicle to the gym about 10 miles from my house. At mile 7 it started acting up. With the engine running (and idle slowly climbing towards the 1500rpm mark) I reached in and felt around for hot spots on the fuel lines, there were none. The fuel filter container was full to the top. The carbs, fuel lines, fuel pump (etc) were all cool to the touch.

As I mentioned before, dumping cool water on the carbs / lines did nothing to resolve the issue and the idie continued to climb.

I am now more than ever confident that there is some kind of fuel delivery restriction. I will report back as soon as I get a minute to work on it.

I just wanted to say thank you for everyone's help... whatever the cause of this issue is, this outpouring of support, advice, tips and tricks has been the most comprehensive, least cynical first thread I've ever started on a website. I've been running around online automotive forums for 15 years now and this is one of the few where when a new person asks for help, everyone doesn't scream at them to use the search feature... which FWIW I have been doing since January trying to figure this issue out but thanks for not screaming at me to do so.

So again, thank you all for your time, I will let you know what I find. Hope to see some of you at Z-Bash (Motorsport! Car Shows & Events - The Z Store, Nissan-Datsun 240Z-260Z-280Z-280ZX-300ZX(Z31/Z32)-350Z-370Z Parts) this upcoming weekend. I'll be the only guy wearing a Volvo Motorsport shirt.

Cheers,

Ryan

[240260280z]

Maybe try daining tank to see what comes out.

I you have debris then try running it from a jerry can of fuel (send and return to it),

an you take a photo of the plugs. They could be fouling, Use NGK or Denso if you have them

try disconnecting the choke cables and pushing the jets all the way up too

[madkaw]

I would say it's time to eliminate the fuel system. either drop the tank or just drain it into a pan to see what gives. Pull the fuel sending unit and check both supply and return-blow thru both. I would remove the fuel rail an make sure the return side is not obstructed. Pull the inlet sides of the SU float bowls and check the filter there. Also check the fuel hoses from the float bowls to the carbs to make sure they are not collapsing under heat. The ignition next

Good luck

[jalexquijano]

i am having a similar problem and maybe considering on reverting to the original camshaft as the car is tending to fail when it is between 800 to 2,000 RPM. Once it reaches over 3,000 RPM it is really stable.

The car actually has the following specifications:

New Datsun L24 motor with crank and rods from a L26, special oversized 84mm flat top black coated pistons from D.L. Potter Engineering with E88 Head and Far 311 New Race Cam.

2 original SU Hitachi round top carburetors rebuilt.

Tomorrow i will have the best carburetor mechanic here in Panama, Central America where it is 32 degrees Celsius to fix this problem. I will appreciate if someone can provide me with a list of things he should check to get this stalling problem solved.

[TheGrimOne]

Before messing with fuel lines, if your z has an EGR valve, thats the problem, your taking in to much cool air at operating temp and its limiting combustion, plus you said the plugs were kinda fouled so thats a rich run, meaning somewhere your car is starving for balanced air. Throttle body probly has plenty of carbon deposits and will help the problem. If the EGR is faulty in some way it will mess with combustion, the throttle body, and the exuast system is likely to clog up 30 percent faster or more. Why I say EGR first is cause all you need is a EGR valve gasket ( like 2 bucks ) and a can of carb cleaner with a wire brush, and a couple hours to clean the EGR. The EGR is supposed to start working at op temp, and the vacuum works it, mine was sticking and gave me all kinds of issues, I replaced all fuel parts including the tank, and my running problems turned out to be that sticky EGR. Might as well check the simple cheap stuff first. The PCV hose will be clogged to. My Z became perfect after cleaning the EGR and throttle body.

Assuming you have one of course, im in california so all Z's here have 1.

[madkaw]

Did you even read the first post before answering-

Before messing with fuel lines, if your z has an EGR valve, thats the problem, your taking in to much cool air at operating temp and its limiting combustion, plus you said the plugs were kinda fouled so thats a rich run, meaning somewhere your car is starving for balanced air. Throttle body probly has plenty of carbon deposits and will help the problem. If the EGR is faulty in some way it will mess with combustion, the throttle body, and the exuast system is likely to clog up 30 percent faster or more. Why I say EGR first is cause all you need is a EGR valve gasket ( like 2 bucks ) and a can of carb cleaner with a wire brush, and a couple hours to clean the EGR. The EGR is supposed to start working at op temp, and the vacuum works it, mine was sticking and gave me all kinds of issues, I replaced all fuel parts including the tank, and my running problems turned out to be that sticky EGR. Might as well check the simple cheap stuff first. The PCV hose will be clogged to. My Z became perfect after cleaning the EGR and throttle body.

Assuming you have one of course, im in california so all Z's here have 1.

[mckennar]

Yeah I mean I really don't know what to say here TheGrimOne... the car is a '72 with carburetors so no throttle body. No EGR but an air pump that is now in the "closet o' forgotten parts" along with the original exhaust manifold. Thanks for the effort, but it's decidedly misdirected.

A small update - my landlord about had kittens when he caught me elbows deep in the engine bay this past weekend. He started blabbing about a part in my lease that says no working on cars blah blah blah fines blah blah blah eviction etc. Anyways, I haven't been able to drain the tank yet. I'm probably going to tow it to a shop unless I can drain and drop the tank and blow out the lines on a weekend where he's out of town. Will keep this thread updated as I get further into it.

[TheGrimOne]

your right about the TB, dont know why i threw that in there, just the middle of a rant i suppose, but i had a 73 240z thats was carbed and had an egr, thats why i was askin about yours.

[mckennar]

Update - blew out the lines w/compressed air, drained and filled the tank, replaced the brand new fuel filter with another brand new fuel filter... drove 3 miles, stalled again. Waited 10 minutes, drove 1.5 miles, stalled. Waited 10 minutes, drove 1.5 miles, baaaaarely got it into my driveway and it stalled again.

I'm thinking I have about 20 different issues to tackle, not the least of which are vac leaks, exhaust leaks, etc. Realized these things have power brakes yet I have to apply about 80lbs of force on the pedal in order to initiate braking. Thought it was like my Demon and '66 Mustang w/o power assist brakes. Guess not. Applied shop vac to master vac, magically brakes became easier to press (engine off). Started engine and put my thumb in the line to the master vac, it barely had any suction at idle at all. All signs are pointing to a massive vac leak... which is weird because it idles rock solid at 500-600rpm when warm. I must have missed something when I pulled the air injection equipment.

Also, carbs are original and have never been rebuilt. I looked through 32 years of receipts over the weekend and never saw anything about the carbs.

I'll update this thread when I get this thing running properly.