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

Greetings to everyone, I am asking for help from more experienced colleagues. I have a 1953 Packard Clipper, 288 cu.i. engine, two-barrel Carter WGD carburetor.
After driving 2-3 miles, probably after warming up, the engine starts "coughing" and "backfiring." It's as if it's not getting enough fuel. The engine loses power. After starting, when the engine is still cold, everything works normally. The pump provides enough fuel, see the picture of the fuel bowl. (When I disconnected the fuel supply hose to the carburetor and cranked the engine, fuel flowed normally from the pump hose). I think the problem is in the carburetor. I tried to adjust it according to the manual, but something is probably wrong. The mixture richness screws are opened 2.5 turns. Can anyone advise me?
Thank you.
Stajgr

The float level may be too low. When the engine is cold, the automatic choke should be engaged. That could mask a low float level condition. If that's the case, and as the engine warms up and the choke opens, it could get too lean, especially under load. If it only backfires and lurches at the moment you open the throttle, it could be a problem with the accelerator pump. I would also try removing the fuel filter and see if that helps. A number of fuel delivery issues can get worse as the engine warms up. Add on fuel filters can cause problems.
(The adjustment screws primarily affect engine idle, and if the engine runs OK at at idle, they are probably OK)
Under some conditions, carburetors can form condensation or even frost internally, and that can disrupt engine operation. That problem usually occurs in cool damp weather, and it usually disappears after the engine is fully warmed up.
An inoperative manifold heat valve can contribute to carburetor "icing".

Did this appear rather suddenly, or has it slowly become an issue? If your engine was being starved of fuel I would expect a general loss of power, and maybe even dying, but not necessarily the symptoms you're describing. Here's another potential issue to consider. If you're coil is bad, as it warms up it will can cause all kinds of ignition issues, and because they are random in nature they appear to be fuel issues.

I just went trough this a couple of weeks ago after going for a drive to see some friends. The car was developing a miss which was even notable while driving, something completely new. The car sometimes has a bit of a miss when warming up, but once warm it's pretty smooth............like a Packard should be!

When we got home I popped the hood and started poking around to see what I could find. As I was checking to make sure I didn't have any loose plug wires going into the distributor I noticed that a couple of them were slimy.....what's this??? It's like they had oil on them, which they did! My NAPA coil, which was only a year old, has leaked out it's oil, which it uses for cooling. The coil was overheating and causing the engine to misfire, stumble and just run terrible. Replaced the coil with a Flame Thrower and my car has never started and run so well!

There are a few videos on YouTube showing how to test your coil.

The Flame Thrower may be so hot that it could cause insulation breakdown in the older model ignition parts. It also may draw enough primary current to shorten ignition point life. A resister in series with the coil primary will tame it, if problems arise. Ideally, the coil and condenser values are matched. That said, I used to have a very hot 6 volt coil, and it gave no problems except it could throw a spark from the coil wire contact in the distributor cap to the plug wire contacts. It worked best with a resistor in the primary circuit. (1954 Ford Y block V8)

Coils can overheat if the ignition is left on with the engine not running. I had a coil explode on an old Plymouth. It go so hot it blew the top off and spewed hot oil everywhere.