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Thread: 1972 Datsun 240z with stock SU carbs stalling at intersections! How do i solve this?

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    Default 1972 Datsun 240z with stock SU carbs stalling at intersections! How do i solve this?

    Just purchased a 1972 Datsun 240z from a Dealer in Colorado where it is cold. The car was shipped to Panama, Central America where the temperature is 32 degrees Celsius (Hot Weather). Anyway, i had to remove the thermostat as it was taking the temperature needle more than half way. The car Works perfectly and mantains the needle at half of the temperature gauge for the first 25 minutes. After that time lapse and whenever i stop at any intersection light the RPM starts to drop to 600 RPM with the intention of stalling, so in a rush of not being dumped in the road i drove to my house and kept the car in idle for 2 minutes when it finally shut down. Could this be a carburetor adjustment problem even though the seller advertise them as fully rebuilt? the front 3 spark plugs have turned black, the rear 3 spark plugs are clean. As background information the seller did the following changes in the car:

    ◾PerTronix Ignition Kit with new coil
    Electric fuel pump
    ◾Recent rebuilt Engine
    Recent rebuilt 5 speed transmission from 280Z with new Center Force 1 clutch with stainless steel clutch hose
    New Twice Pipes Exhaust
    60-Amp Alternator upgrade kit
    New fuse box
    New Fan belt with new upper and lower Radiator hoses
    New 3 row Aluminum Race Radiator
    New Plug Wires
    New Thermostat and oil pressure sender
    New brake system with stainless steel brake lines
    New struts
    Rebuild Carbs

    The engine and transmission have less than 6000 miles on them. The following is a list of upgrades or modifications made to the car:
    New Datsun L24 motor has 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.

    Please be advised i have not changed the spark plugs, oil filter and oil to this car since i received it last week. I just want to be sure how to tackle this stalling problem before i do a tune up. It is really weird the car begins to stall after it has fully warmed up.

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    Registered User siteunseen's Avatar
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    They run better with a thermostat. Nissan recommends 170 degrees for tropical temps. Also try spinning your fan, if it spins too easily the fan clutch maybe worn out. Maybe 1 revolution with your hand on a new one, cold, they're oil filled.

    What does the needle show after 25 minutes? Colder?
    Last edited by siteunseen; 02-21-2014 at 09:58 AM.
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    1972 240Z #918 New Sight Orange
    1977 280Z #305 Light Blue Metallic
    1972 240Z #110 Persimmons Red

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    Check the dampener oil level in the carbs
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    Dave
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    1972 240z, restoration in progress
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    A man on a mission Jay Gadsby's Avatar
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    I had a similar problem with my old 12A RX-7 and after replacing damn near everything on the top of the engine, it turned out to be a vacuum line under the intake manifold had come uncapped. For what ever reason, it only died while warm. Cost me 55 cents to fix. At least I had a good tune up. Check ALL your vacuum sources.

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    Jay, Thanks for that bit of info. My son's 12A RX7 is developing that same problem. Now I know where to look.
    Mark in Portland

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    Check out technical article: Quick and dirty SU tuning. There are some other links, and FSM for more complete tune, but that should get it running. For me, the FSM carb tuning is (almost) complete and easy.

    Rebuilt carbs doesn't mean they're tuned.

    When my choke was sticking I had to clean the front three plugs with a wirebrush every few days to keep it running, until I noticed the sticky choke. Carb cleaner and spray grease fixed the choke in ten minutes.

    Picture of car?
    Last edited by Stanley; 02-21-2014 at 12:14 PM.

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    Registered User siteunseen's Avatar
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    Quote Originally Posted by Stanley View Post
    Check out technical article: Quick and dirty SU tuning.
    I have that in my favorites, http://www.classiczcars.com/forums/s...su-tuning.html
    1972 240Z #918 New Sight Orange
    1977 280Z #305 Light Blue Metallic
    1972 240Z #110 Persimmons Red

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    Assuming the carbs were correctly tuned for Colorado's elevation and then moving the car to a new elevation you should re-tune the carbs. With EFI this is not a problem as they can adjust for it. Carbs you have to re-tune to adjust for the change.

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    Registered User beermanpete's Avatar
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    Have you put in new gasoline from the local area? Perhaps the fuel is a winter formula fora cold climate and it is vapor locking in the hot climate. Also, is the electric fuel pump in the front (engine compartment) or the rear near the fuel tank? Placing the fuel pump close to teh tank helps prevent vapor lock.

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    First thing I'd check for is to make sure you have a little slack in both choke cables to see if the FAT carb's choke is being pulled "On" slightly when the choke is off. That assumes that both carbs were tuned the same at some point previously.

    If cables are okay then run that FAT carb nozzle up a half turn and drive it. That carb is running rich for whatever reason and you just want to lean it out some.
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    Drove the car today for an hour, so heavy traffic and hot day. The temperature gauge needle started increasing until 3/4 of level and the car tended to stall in the traffic so i had to open up the choke a Little bit to increase rpm. I checked the fan clutch and it does not spin easily. Please be advised that i am running the car with no thermostat. I already changed the spark plugs, oil filter and oil of the car. The temperature issue is really annoying and it only happens when the car is under hot day and traffic. What should i do?

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    No more body roll! SteveJ's Avatar
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    Put in a thermostat. The cooling system is designed to have that restriction in there.
    73 240Z
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    A fan shroud helps too, when you're stuck in traffic on a hot day.

    Without the restrictor, coolant might go through the radiator too fast, not giving it time to get cooled off.

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    Registered User Stanley's Avatar
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    Also, I expect The pitch of the WP impeller would have been designed to work most efficiently with the thermostat in the system.

    Real Nissan thermostats look like they're made better than the chain store type.
    Last edited by Stanley; 03-29-2014 at 07:00 PM.

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    I was having the same issue with my 71, stock su's when stuck in traffic here in Florida. There is a laundry list of issues it could be. However, I would start with the cooling system. Make sure you have proper coolant mixture/level. Thermostat is important as well. Clutch fan should be checked for proper function. Next is tuning carbs- correct mixture and air flow. Next is checking timing (if too retarded, you will run hotter). If still persists after all if the above, you might have to consider whether you are having fuel percolation and/or vapor lock (that is what I had. Fixed by switching to electric fuel pump and wrapping my headers...but this was AFTER dealing with cooling system, carb sync, air/fuel mixture)...

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    Quote Originally Posted by ronlaw28 View Post
    I was having the same issue with my 71, stock su's when stuck in traffic here in Florida. There is a laundry list of issues it could be. However, I would start with the cooling system. Make sure you have proper coolant mixture/level. Thermostat is important as well. Clutch fan should be checked for proper function. Next is tuning carbs- correct mixture and air flow. Next is checking timing (if too retarded, you will run hotter). If still persists after all if the above, you might have to consider whether you are having fuel percolation and/or vapor lock (that is what I had. Fixed by switching to electric fuel pump and wrapping my headers...but this was AFTER dealing with cooling system, carb sync, air/fuel mixture)...

    I checked the fan yesterday when the car was cold and it is not spinning freely. If you turn it, it does not spin the full cycle. If this is the case, should i order a new fan clutch and wáter pump with gaskets also? Who sells origina OEM Nissan fan clutch and wáter pump? My car was made in January 1972 and carries a plastic fan blade

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    Quote Originally Posted by jalexquijano View Post
    I checked the fan yesterday when the car was cold and it is not spinning freely. If you turn it, it does not spin the full cycle. If this is the case, should i order a new fan clutch and wáter pump with gaskets also? Who sells origina OEM Nissan fan clutch and wáter pump? My car was made in January 1972 and carries a plastic fan blade
    Sorry for the delay.
    Not sure whether its the fan. Give a little acceleration and see whether the fan clutch engages. At idle, the clutch won't engage fully.
    Check out Welcome To Motorsport & The Z Store! Nissan-Datsun 240Z-260Z-280Z-280ZX-300ZX(Z31/Z32)-350Z-370Z Parts!, Datsun 240Z, 260Z, 280Z, 280ZX and Mazda RX7 Auto Parts & Accessories, or eBay for replacement parts. I found a rep!acement assembly a couple of months ago on eBay for less than 100.00 .. I'll try to get you the link.

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    I've never had overheating issues with my Z, but others here in MN have when it gets really hot and muggy, especially in Twin Cities traffic.

    What my PO did as a precaution was install an electric fan with a manual and temperature-controlled switch and took out the stock fan and clutch assembly completely. He also installed a 3-row aluminum radiator with a 180 degree thermostat.

    As I mentioned, I can drive the z on hot days, sit in traffic, run it in a parking lot, and it never goes above 190. Of course, we have 2 feet of snow on the ground still, so maybe it just so cold here in the winters it never really warms up!
    Current Z: 1971 Datsun 240Z, 3.1 Stroker (F54 block, P90 head, 490-290 cam, triple Webers); 95% complete
    First Z: 1972 240Z, destroyed in a shipping accident. Ack!

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    Just to let all of you know that i replaced the wáter temperature sensor, the old original thermostat housing and swapped the thermostat from 180° to 160°. I tested the car under heavy traffic on a hot day and the termperature in the gauge only raised to half and a Little bit to the right. Othewise it keeps under half. So this problem is solved!

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