I posted a week or so ago about my idle being ever so slightly rough...not a big issue, but bothersome non the less. The use of carb cleaning additives corrected the problem...to nearly perfect idle all the time.

Well, the problem was the wrong carb to manifold spacer / gasket.

Mine had a spacer type gasket, about 1/2 thick.I had no idea if this was stock or not on a 1977 era intake and carb. It was completely cut out in the center, no division between any bores. I replaced with a standard Q jet gasket about 1/32 thick, with division between all 4 bores and much more area under the carb. Presto....idle perfect, a bit better acceleration and overall operation.

PS, I had planned on sorting this out, so I ran the tank nearly empty and filled up with no additives last Thursday.

What got me going was actually a post about about idle not going below 1000 even with no screw contact, and this being a sure sign of a air leak. I had the same issue, although I was around 800-900, so it was tolerable. My idle will go as low as I care. The spacer gasket had hard bushings that were preventing the crush needed on the old gasket / spacer material. I am assuming this was one of those products designed to insulate carb from heat. Mine is hot restarting fine...soo it was not needed I guess.?

I hope this helps someone out !!

 

I went through the exact same deal.
You could get a good idle in the garage & then go for a test drive & the idle would just go to hell. Is it one of those thick gaskets that come in the carb kits? Thats what I was useing. Went & got a Mr Gasket thin 4 hole gasket figured what the heak I've tried everything else. & it worked! Much more stable idle.
Also my engine seems sensitive to underhood heat. So the factory 76 single snorkel air cleaner with the over the radiator airbox is going back on as soon as my air cleaner - airbox hose gets here.

 

No, I believe mine was a dedicated insulator type, actually a bit over 1/2 inch thick. It was there when I purchased last July, on a 77 year engine transplanted in my 81 with no smog stuff at all. Someone did a real nice job welding up the stock EGR, and installing the engine....nothing rigged. I am not sure if the problem was just a vacuum leak, as the solid bushing at the 4 mounting holes were preventing a tight fit on the old, shrunk material, or a issue with the transfer slots and other tracts that were not covered between the primary bores, or BOTH ! Whatever it was, it was very minor, and most folks would have been satisfied with the idle. I knew it should be better, and now it is, without adding crap to the tank !!

 

On a 75, stock gasket is the thick type with the 4 hard spacers at the stud holes.....just for information!