Bad accelerator pump? With the engine off, if you open the throttle does it squirt healthy streams into the front throats?
You NEED the accelerator pump to start the motor on a car or truck with a Carburetor..... Exception to the lawn mowers and many other small motors..
It depends on a few things, but generically; On a car that is tuned correctly and the carb operates properly. Depress accelerator fully to the floor and release. This sets the choke and provides a prime shot. If the car has been sitting for four hours, it will cool sufficiently that the choke likely will set to a lessened choke position, but the prime shot will still be required. Add to that, ethanol evaporates faster when engines are hot, so often requiring a shot on some cars, even when warm/hot.
Mostly true. Virtually all carbureted vehicles that aren't grossly rich at idle need "some" pump shot for quick starting. If your vehicle does not have a functioning choke, and you don't need to pump the pedal or baby-sit the idle speed...it's pig-rich. Less important to this discussion--the choke is likely to fully-close at temperatures higher than most folks expect. Thus the critical nature of the choke pull-off. (Some carbs have two pull-offs.) Certain carbs have NO pull-off, and the choke action has been compromised due to cost-cutting, and the knowledge that the consumer isn't sharp enough to notice the difference since any car with their "hot-rod" carburetor probably isn't used in actual "cold" weather anyway. I would not expect to need a "full" pump of the pedal when outside temp is moderate, ESPECIALLY on a "performance" carb with a big--or twin--accelerator pumps. As the temp cools, a progressively-larger amount of throttle movement (more accelerator pump-shot) is needed. Example: At 80 degrees F, perhaps only enough throttle pedal movement (1/8 pump?) to allow the choke to set. At 40 degrees F, maybe half- or 2/3 throttle. At -20 degrees F, perhaps two full pumps. As said--this is going to vary depending on the pump shot CCs, and the individual engine.
On my race car with Dominator (no choke) if I pump it a few times and try to start right away it fires and dies. BUT if I pump it and let it sit 2min and try it fires immediately and runs great even after 6 months sitting. Took me 30 years to figure this out. I believe it is due to having nice VAPORS under the throttle plates. Vapors light much better than liquid fuel.
