84' 720 Z24 Rough Idle

[Daveg39]

I have a 1984 720 pickup, Z24 engine. My problem is a very rough idle (i.e. stalling, spitting, sputtering, etc…) it runs good as soon as it’s past idle. I set the idle at 1200 RPM just to keep it running. All the pollution controls have been removed. I asked the previous owner and was told the problem was there before they were removed. I did a compression check, all four are at 175 PSI, after numerous other test’s I found the motor is running very lean at idle. When I close off the intake air with the choke butterfly it smoothes right out. It has good fuel pressure and I used a smoke machine to check for vacuum leaks and there is none, it’s pulling 21 inches. All the vacuum components, choke pull off, brake booster, etc... are OK. I removed the carburetor and cleaned, checked all the passages so many times I can do it in under fifteen minutes now! I checked the anti diesel valve and even ran it with it removed, enlarged the slow run jet, I can turn the idle mix screw all the way in and it makes no difference. I believe I have it narrowed down to the carburetor, but what is it in the carburetor? I hate to cop out and buy a Webber, I’m sure this truck wasn’t sold new with a bad idle. Can anyone solve this riddle? I hope someone out there is raising their hand going oh, oh, I know, I know!!!

[zanegrey]

route the vacumn to the fuel pressure regulator from a direct vacumn source..

and idle it down..