my 67 olds 425 has developed a rough idle. It acts like a vacuum leak, it disappears when I raise the rpm. Used carb cleaner everywhere to check for leaks, nothing happens. Anyone got any ideas ?

 

Hopefully not old or contaminated gas, add a can of seafoam, lucas, or preferred brand of fuel treatment in a full tank.

If you've sprayed all the vacuum lines, gasket areas (both manifold and carb to manifold), Pull your air cleaner and ensure your choke is completely disengaging. Also look into the air horn of the carb and see if its dripping fuel at idle. If not then I would pull both my A/F mixture screws and spray some carb cleaner in the ports, and recalibrate. I would also place a rag over the air horn or your hand, while its running, so the engine almost stalls and release. I would do this 2-3 times to possibly unstick metering valves.

If its none of the above then I would pull spark plugs and look for fowling. Check all ignition parts and wires, fuel filter, PVC, etc...

Good luck!

 

NEVER USE A RAG!! You could pull it in the carb and start BIG problems!!!!

Rev the motor to 3500 - 4000 RPM and use your hand - pulling any 'junk' out of the idle circiut!
If that straightens it out, somehow dirt is getting through the carb, and I'd be changing fuel filters.

 

Thanks for ideas, pretty much did all of what you said with the carb already. Changed the plugs 2 weeks ago. The miss showed up after that , may have gotten some bad plugs. The old ones were pretty clean, no gunk build up. Guess I'll get another set see what happens.

 

You might have broken a spark plug wire, too.
Carefully pull them one at a time, while running, to tell which one it is.
Will also point out which plug is bad!

 

Finally got around to changing the plugs this morning. Smooth as silk now. Either a bad plug or the unlikely possibility I didn't get one of the wires on tight and it worked loose. Egotistically it has to be the former.
Thanks for the ideas.

 

LOL, glad its fixed!