Packard Forum Index » Post-War (1946-54)

51 is running good, drives nice and smooth, but when i get it up to operating temperature and kill the engine , it will not start up again until it cools down unless i put hand over carburetor to full choke it , then it starts right up. any ideas on what this problem could be?

Pump the accelerator one to no more than 3hree times before trying to start.

tried pumping 1-8 times trying to start between each pump and no luck unless i fully choke carb by putting hand over throat of carb

Strange. Almost sounds as if the acc pump isn't doing anything. Can you see a nice stream of gas squirt in carb when pumped?

will check that tomorrow and post result

Have you checked the valve lash ? When the engine warms it might be loosing a little compression ? Also check the heat riser.

I suspect you've got a vacuum leak somewhere. Choking the carb is helping to offset the excess air.

Brian, How big of a vacuum leak would it take? Almost mentioned that in my post because it needed the enriched mixture but first question post said it was running nice and smooth otherwise. Figured any vacuum leak big enough to cause the hard start would make it run like crap. Not being much more than the basics of an engine guy, what am I missing here?

Choking the carb with your hand on an idling engine is an old trick my dad taught me; if the idle quality improves, you've got a vacuum leak.

I can't say how big of a vacuum leak it takes to cause a hard starting problem with a warmed-up engine, but any leak below a closed throttle plate is going to work against what the carb was designed to do.

I've seen some pretty small leaks in the base gasket make for awfully hard starting. Yet, I've seen engines with (what turned out to be) a leaky distributor vac advance control that had been tinkered with enough to provide a reasonably smooth idle, but exhibited hesitation under acceleration.

One problem is that we don't know what the service history of this car is. So, I'd say it's time to start squirting a little carb cleaner or even water (the latter from a trigger spray bottle), with the engine warmed-up and idling, to test gaskets, the throttle body and shafts, and vacuum connections and watch for change in idle speed/quality.

Free of vacuum leaks and properly tuned, I can start my warmed up V8s without touching the gas pedal. I suspect a Packard straight eight can perform just as well in that regard.

Gerd -

I bet that the manufacturer of the carburetor, let alone Packard, never expected these vehicles to still be in use so many decades later.

After so many years of operation and/or neglect, it is entirely possible that shaft-to-bore clearance in the throtle body has become execessive. Decades ago, as a newbie, I never considered that possibility until I met a fellow at Fall Hershey who restored carburetors; he advised that, as part of his service, he machined the bore and shaft to accept a bushing.

So, once the general area of the vacuum leak has been found, one then needs to focus their search. An aerosol carb cleaner with an extension wand works well for pinpointing areas.