I have a Holley 4548-S carb, Ford  P/N D0PF-9510-U giving me problems.  Drove 250+ miles on Thursday, climbing 3500 ft in the 30 miles, no problem. Drove around at 4000 ft. for a couple of days, maybe 75 miles, no problem.  Went to leave this morning, and the car wouldn't idle.  Stopped for gas at about 100 miles, engine temp about 180 still wouldn't idle.  Stopped for lunch at about 180 miles, in neutral at a fast idle, maybe 1200 RPM the engine would surge regularly, my wife thought I was moving the throttle to keep it running.  Engine temp close to 200, ambient temp around 90.  Finally got home and backed in the garage and could smell what seemed like a rich mixture.  The whole time it seemed to run well at highway speeds, 65-70 or so, though I might have felt a little surge.

After the engine cooled, I decided to check float levels, gas didn't pour out the check screws, but would splash out a little for the few seconds it tried to idle.  One thing that caught my eye was the fuel bowl was almost empty before I started it, though it did fill right up.  The more troubling thing is on the rear bowl where the fuel delivery tube enters there is a fuel leak, not the o-ring on the tube, but on the side where there looks to be a pressed in plug, it's leaking around the plug.  I've had a fair amount of experience with Holley 600s which are very similar, but haven't seen this leak before, and it doesn't seem to be something that would affect idle.

Any thoughts or help would be appreciated.

Thanks,
Don

The primary bowl being low on fuel prior to starting the engine leads me to believe the power valve may need to be replaced or at the very least, tightened.

Lorena, Texas (South of Waco)

Ted beat me to it. Would go after PV.
If not that I would start with the usual suspect vacuum sources. (PCV etc)

Mike Rizzo

1963 F100 "Rudy"

Daniel Island, SC

Once you address the power valve, try shooting some carb cleaner into the air bleed holes located just fore and aft of the venturies when looking from the top of the carb.  These can get dirty and affect overall running of the carb.

Lorena, Texas (South of Waco)

do you have a fuel filter(the type that is a ad on,and you can see threw.If you do could be the glue disinegrating.I have had similer isue and the NAPA fuel filter glue disinigrated and the pieceses held float open.hapened on2 ocasions. some say it is the ethenal in fuel,on checking the package(made in china). they gave me a replacement in a can,now i wonder about what i cant see.

Thanks for all the advice, but still having problems.  Vacuum seemed ok, made sure the PCV wasn't leaking, vacuum gauge read about 15 which seemed low, but could be a function of the way the engine is running.  Power valve seemed ok, but changed it anyway,  

I think I found the problem though, at anything over an idle, the passenger side primary venturi is pouring gas in.  The float levels are correct.  I've got a yard project going now, but hopefully I can get back on it in a day or two.

Thanks again,
Don

In the metering block is a pair of anti-siphon holes located in the fuel feed channels close to the top of the metering block.  These are simply air breaks to keep the fuel from siphoning over into the discharge nozzles.  These holes are quite small but can get plugged on engines using ethanol laden fuel that do not get driven regularly.

Lorena, Texas (South of Waco)

Ok, I think I located those holes and couldn't spray carb cleaner through them.  Now i'm soaking the block overnight in some old carb cleaner I have.  By old, I mean probably 25 years and getting a little funky.  I'll try again tomorrow between laying brick and running sprinkler wiring.

Don

After soaking the metering block overnight and cleaning out the passages, it idles decently, though a little low when in gear, but I haven't even started readjusting the idle mixture screws.

Thanks again,
Don