Idle Drop.....what's normal? adjustment?
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,713
Likes: 31
From: Shreveport LA
LA Events Coordinator
Idle Drop.....what's normal? adjustment?
I have a 75 350 with automatic transmission and a mild cam I just recently (1 week ago) had the Holley 670 rebuilt by a reputable carb/fuel injection shop. When the car's running "right" the idle rpm in Park=750; in Drive= 600...the timing=6 degrees. Now, after getting the carb back, the Park idle=900 and the Drive idle=500 and it sounds like it's going to die. 
Before reinstalling the rebuilt carb, I replaced the spark plugs and plug wires. After installing the carb, I checked the timing...still 6 degrees. Here's the question: I would like to get the engine BACK to 600/750....how do I do that? I adjust the curb idle screw on the carb and lower the Park idle to 750 BUT when I drop it in Drive...RPM's drop to 400 and almost dies 
WHY and HOW do I fix it? I checked the fuel level in the bowls....perfect! HELP!!!
Before reinstalling the rebuilt carb, I replaced the spark plugs and plug wires. After installing the carb, I checked the timing...still 6 degrees. Here's the question: I would like to get the engine BACK to 600/750....how do I do that? I adjust the curb idle screw on the carb and lower the Park idle to 750 BUT when I drop it in Drive...RPM's drop to 400 and almost dies WHY and HOW do I fix it? I checked the fuel level in the bowls....perfect! HELP!!!
Melting Slicks
Joined: Jun 2001
Posts: 2,264
Likes: 546
It sounds like the 2 air-fuel idle screws need to be adjusted. Turn them in and count the turns to seat them DON'T FORCE them.. Then back them out and make sure they are both the same. Turn them both a 1/4 turn at a time to get the highest vacuum reading or rpm. Then set the idle, Hope this helps. Ron B.
Set your idle mixtures - sounds like you need to richen it up just a tad. You also don't have enough timing in it...
