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

[jalexquijano]

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.

[siteunseen]

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?

Edited February 21, 2014 by siteunseen

[Jarvo2]

Check the dampener oil level in the carbs

[Jay Gadsby]

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.

[Mark Maras]

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

[Stanley]

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?

Edited February 21, 2014 by Stanley

[siteunseen]

Check out technical article: Quick and dirty SU tuning.

I have that in my favorites, http://www.classiczcars.com/forums/su-carb-technical-articles/41940-quick-dirty-su-tuning.html

[jwtaylor]

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.

[beermanpete]

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.

[Bruce Palmer]

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.

[jalexquijano]

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?

[SteveJ]

Put in a thermostat. The cooling system is designed to have that restriction in there.