I have been given an old Datsun 720 4x4 ute. I t has been sitting idle for some time and when it did run it was rough. I have replaced the carby as the old one is rusted up, but it wont run,unless you poor some fuel down the carbie and then it fires but wont run at all. I'm not sure if its electrical or fuel as I am getting spark. Cheers Ray

Is it carby model or injected.

Turning on the AC forces the idle to rise, if it is working as designed. It may be masking the problem. How does it idle after warmed up and AC off, all accessories off?
Check idle speed, idle mixture needle (if accessible-some are plugged off with anti-tamper metal seals) and do check timing if you have a rough idle. Timing could be spot on, it must be close if it runs perfect, just make sure it is within plus or minus 2 degrees of specifications at specified idle speed, and vacuum advance hose disconnected and plugged off.

Well, good luck with the old dinosaur, lol, as an owner of a '79 Datsun pickup, and now an '87 sedan (Nissan, of course!). We will run them into the sunset together!

Sounds frustrating, and given the extent of the work done it could be almost anything. It could be something simple, like a bad spark plug, or something major like an incorrectly aligned timing belt. It sounds to me like a vacuum leak somewhere. I would call the shop back and be sure they spend some time trying to track down the problem. If they claim it wasn't their fault, get a second opinion.

Compression blow-by on the piston rings is pushing oil out.
Just a sign of a worn motor.

It sounds like a idle switch on the carbie easy to replace

youll probably need to get a repair manual online or check with garages that have been around for a long time they may have the old ones still

BUY SOME GASKET SEALER LIKE RTV SILICONE BLUE TYPE RESIST ANTIFREEZE.

make sure leads are all connected to the proper plugs!
is it a 4 or 6? a 4 would really run rough! also check spark timing.
good luck!

YOUR problem is the carby acc pump and idle jet ...... what you need to do is remove airfilter and take the top off the carby and you should see a small ball and spring under gasket ...when you open the throttle it will pump petrol to the small pick up jet and the other jet will take over ...clean out carby jets and rebuild and that should be ok

a diagnostic computer check from your local ford dealer will sort that problem for you,the cost for that check should be around $50 and from then on whatever the problem wil cost you whatever your local dealer charges for labour or unless of course you are able to do it yourself which is cheaper in the long run,hope that helps,,goodluck.