Rough idle until 1000 R's???? Help!

Lady at my work, not much money, trying to help her out....

Late model 350, edlebrock 500 carb, vaccum advance distributer. Checked all the vaccum hoses because it seems like a vaccum leak. Everything appears "OK". Cleaned the carb with B-12, checked the distributer and it's tight, so it hasn't moved from when it was running good. Sputters and idles rough up to 1000 r's then clears up. No missing when the r's are up either. Plugs are tight, wires are good.

Any suggestions? Am I overlooking something simple? Thought about replacing all the vaccum hoses and putting a new carb gasket on.

Thoughts...????

Any suggestions would be helpful.

Thanks,
monkey

 

spray some carb cleaner around edge of intake and around carb while running.

 

Check for a stuck metering rod.

It's probably bent as well.

 

I did this and nothing seemed to happen. Maybe a little change on the right front corner. But it was too hard to tell.

I will check the meetering rods. Can they just get bent on their own??? This carb has never been apart until last night.

monkey

 

Engine have a lot of miles on it? Could be something dastardly like a bent or burned valve. A compression check could eliminate or prove that possiblility quickly and cheaply.

But on the onset that sounds like a classic vacuum leak.

 

I'm guessing a manifold to head sealing leak...

 

It seems they get bent prior to installation, work ok for a while and then hang up.
Happened to me with a Carter 500 purchased new.
Ran great for a few weeks and then it had the same symptoms you're describing.
Nice part is, it's easily checked.

Remove the rod, remove the rod piston, roll the straight part of the rod on a flat surface and you can see mild bends pretty easy.
Use care in straightening, the rods are fairly delicate.

 

Sounds to me like one side of the carbs idle circuit is plugged, try this, Get some carb spray with a nozzle, remove the mixture screws, spray into the holes, reinstall screws

 

Get back to the basics, hook up a vacum gauge and see what readings you get.

 

Maybe a bad plug wire. Look for spark to ground at night from one of the plug wires. I've see crossfiring from plugwire to plugwire when wires are old and insulation breaks down.

 

my chrysler did that a couple times when the vacuum caps got dried out & cracked. there are a couple of ports where it looks like they were capped from the factory (maybe a vac accessory port on another model?) & those little rubber caps dont hold up forever. plus, you can get a whole pack of assorted rubber caps for a couple bux.

 

Does the AC/heater system air only come out at the floor?
If so, plug the fallen hose back onto the "black ball" vacuum reservoir.
They hide them well sometimes, but they are notorious for coming loose.

Also, make sure the dissy vacuum is sourced to the DRIVER'S side hose bib on the carburetor, NOT the one the Edelbrock instructions say to use.

 

THanks Guys,

Lot's of great ideas. I'll check into several of the suggestions and see what happens.

Thanks again!
monkey

 

check the vacume advance and the modulator on the trans i had one of each go bad and cause a vacume leak Joe

 

check the hose on the transmission vacuum modulator if it has one.... fuckin things.