an unexpected case of nozzle-drip

[omaha]

I know that the idle rpm on a Cadillac is like 600 in gear. So something is causing it to idle faster. Have you delved into the distributor? Sometimes the springs wear out in the distributor and cause erratic timing/idle. [the weights will stick]. Usually you can spot this with a timing light though. Good luck and tell us what you find.

[Marx3]

Timing is rock steady at 6 degrees initial.
It return to 6 degrees after being revved.
I know, cause I tried installing an advance kit, to get the total up a bit.
The total is around 15 stock. Horrible!

The particular advance kit was ( also ) useless, sadly.
I know these 500's really come to life, once the total gets up around the early 30's with a longer curve.

[Marx3]

Just wanted to report back: I ended up putting in another baseplate, that had the secondary plates perfectly centered. This cured the out of control high idle.
This is the second time I have had this problem, with a Cadillac 500 engine.
I guess these big engines are just more sensitive, to the slightest leak past the plates.

[Cliff Ruggles]

I had a big 500 Caddy in here recently to work on.  The owner had completely rebuilt it and it was now 508CID, with an aluminum intake and larger camshaft. 

It had the stock 1976 Caddy Q-jet still in place, but EVERYONE was telling him to ditch it and put a Holley or Edelbrock on it instead.

The owner had the engine installed an older truck (mid to late 50's) sitting on a 1998 Chevy frame.  It was a "rat rod" and we LOVED working on it here in the shop.

He drove quite a ways to get it here, and was determined to keep the q-jet in place.  Quite a few folks had worked on the carburetor so it was "hacked" up a bit.

They had also drilled out the primary jets to HUGE dimensions trying to cure a lean condition at and right off idle.  Of course fuel mileage was horrible.

We went thru the carb, and also discovered that the vacuum advance on his "new" distributor was defective.

We opened up the idle system in the carb and went back with 73 main jets and our 44 primary metering rods.  We fired up the big 508 and it idled down to 600rpms and dead smooth with full control of the mixture screws.

We then fine tuned the APT system and he took it for a spin.  The owner came back grinning for ear to ear, as he told us that before we worked on the carb he was a bit disappointed in the power from the big 508 Caddy engine.  During the test drive he went to full throttle around 20mph and it got sideways in the road!!!!......Cliff