I have the above carb on a 5.0 liter roller cam motor. It has a reground cam to the specs of a '69 351W motor and an Edelbrock Performer Intake.

Here is my question; is it normal that as little as a 1/4 turn on the idle mixture screws would account for excessive sooty fuel coating the white outdrive and floating atop the cooling water running down the driveway.

The adjustments on the carb are as follows; the idle adustment is just off the stop, there is approximately .015 of the transition slots evenly exposed when you turn the carb upside down to inspect. the idle mixture screws are backed out a pretty even 3/4's of a turn. the idle vacuum, at about 575-625 rpm is a fairly steady 14 inches.

Ideally the best idle, for shifting the outdrive, would be 500-550 rpm but I cannot get it down to that.

If I turn the idle mixture screws out another 1/4 turn, the vacumm increases to about 15 inches but that is when I get the excessive sooting.

Does this all sound about right?

Compression and leakdown tests are all good. I'm running an MSD 6A with Pertronix II ignitor so I have a helacious spark. Initial timing is at the factory 10 deg BTDC. All jetting and powervalve is according to List specs for a 302 application.

is the carb in? Is it due for a rebuild? My first look for the overfuel would be to check the float level. Why can't you lower the idle speed?

...I cannot get a lower, stable, smooth, idle. 575-625 is about the best that I can get without stalling out. The carb was rebuilt by me, then rebuilt by a 'professional.