‘70 Olds W-30 4-Speed re-built to stock specifications. Compression was lowered to 9.5 with hardened valve seats. Everything else is stock. Car ran great for 1st 500 miles. Recently the car has suddenly been stalling without warning - both at idle and in gear. Yesterday I started her up - let her warm up and pulled out of the garage. After a minute at idle the car stalled. No knocking or engine run on. Before stalling the idle seemed fine - no roughness. Idle at 750. Car would not restart. Just cranked. No backfire. After waiting 30 minutes she started right up but then stalled again after 20 seconds or so at idle.
Gas is fresh - full tank. Everything in motor is new. Stock carb, wires, it does have GM electronic ignition. Car ran perfectly before this. Timing ? Vacuum leak ? Carb adjustment ? Bad gas ?

 

Which "stock" W30, the MT or AT versions? Cams, carbs, and distributors are different between the two.
Which carb number? Points or electronic distributor?
Is the gas tank and filter sock new? Crud in the tank can get sucked up against the inlet sock and starve the engine, then fall back into the tank when the engine stalls.

 

When it cranks but doesn't start put a timing light on it. Point it to the underside of the hood and see if it flashes while someone is cranking the engine. If not you have an electrical problem, if it does you can look somewhere else.

 

Put a test light on the tach terminal. Crank the engine, if the light should flicker. If not, check the ignition points or ignition module, whichever the case might be.

 

Next time it stalls, check to see if the carb is out of gas by moving the throttle & checking to see if the accelerator pump is squirting fuel into the primary venturi. If not it could be fuel pump. Rubber fuel line connections could be dry rotted & sucking air. One more thing could be the wrong gas cap. If removing the gas cap allows the engine to run you may need a vented cap.