Montecarlo problem

my friend has a 75’ chevy montecarlo with a 350 small block 4 brl. carb. its been running rich because his friend had changed the screw setting on the carb and didnt know where they were before he moved them. i was wondering if any one knew a site to find how the screws are sapose to be set. its either a webber carb or edlebrock. there are 2 stickers on it.


It’s the same carb. Normally the screws run about 1 and 1/2 turns out but these only affect the idle mixture. They have nothing to do with the acclerator pump circuit or the main jets.

If it’s running rich at speed or wide open throttle then he has another problem.

sometimes when he shuts it off it diesles. it seems like it tries to fire over again or something. does anyone know why this happens?

Are you sure he didn’t adjust the idle speed screw? If he set it to idle too high, the car can diesel when you try to shut it off. Dieseling happens when fuel ignites without a spark, basically. If the idle is set too high, then there can be too much momentum in the engine when you turn it off and that will keep it turning and combusting fuel, but not getting spark, giving you that bad sounding coughing and sputtering.

Does he have a tachometer in the car? Take a look at what the idle RPM’s are when the car is warmed up and if it’s over 1000, then it’s definitely too high, but I’m not sure what the idle for a 75 Monte Carlo with a 350 should be. Most cars I’m familiar with are around 700. He can try turning the screw to decrease the idle (try left or right and check the tach to see if you’re going the right direction…or listen to the sound of the engine) and see if that brings it back to “normal”.

Anyway, that’s a start, hope it helps. Some of the experts on this board should be able to give you more in-depth advice.

As ok4450 said, if it’s running rich when there is significant vacuum (ie cruise or WOT) it isn’t the idle circuit.

But to set the idle mixture on most Edlebrock carbs, you follow this procedure:

*Get the car warm and at hot idle.
*Use the idle speed adjustment (the screw on the linkage) to set the RPM at about 550 - 600 rpm.
*Adjust the left-side idle mixture screw on the carb so that the car idles faster. Adjust it so that the car idles slower if you turn it left or right.
*If the car is now idling above 550 - 600, you need to readjust the idle speed screw back out so that the idle is reduced back to the 550 - 600 range.
*Now follow the same procedure with the right side mixture screw, and readjust the idle speed screw so that it is idling at the proper speed.

Couldn’t hurt to look for vacuum leaks, vacuum hoses hooked up wrong, and check the timing, too.