firstvett69

Hi All, Question about my 1972 Holley 4150 uuuhhhmmm its on a ccccaaaamaro Z28, sorry but I get so much more info here and am steal looking for that next 69 corvette. Question is last month I rebuilt my 4150 Holley new fuel lines from the pump like it should be, used a Holley rebuild kit, set the accelerator pump at 0.15 as prescribed because I had a backfire at initial throttle opening fixed that, car starts, runs great at in town and cruise speeds but the darn thing will not idle below 950/1000, the timming suppose to be at 4* I had it at 12* the more the better on these cars but now I'm back to 6* and the idle is at 950/1000 again, cant find a vacuum leak, NONE, so when I rebuilt the carb there is a rear secondary butterfly plate setting underneath the carb on the right rear side below the vacuum secondary arm where it attaches to the secondary rod shaft, If this, or I should say if the secondary butterfly's are open to much can this cause my higher Idle every thing else to my somewhat limited knowledge is OK, after a month I don't even have Any fuel leaks on my newly cleaned and original intake, OK ,for now. Any thoughts would be appreciated. THANKS 1972, Z28, M-22, 4.10s 1of 652

oldalaskaman

http://forums.corvetteforum.com/other-cars-24/

scottyp99

Yes, that secondary throttle blade adjustment will affect idle the same way the idle speed adjustment screw does. Take the carb off, adjust the primaries so that about .020 of the transition slot is exposed when the throttle blade is all the way closed, (make sure the fast idle cam is not interfering, and, I don't mean to be insulting, but in case you don't know what the transition slot is, it's the small vertical slot in the primary bore) then, put the carb back on the untake manifold, start it up, and adjust the idle speed by closing/opening the secondaries. The secondary adjustment uses a small screw that is difficult to get at without removing the carb, but if you are creative, you can get at it with a small screwdriver. Replacing the screw with an allen bolt of equal thread pitch makes the whole thing a lot easier, and once you have it adjusted, a small drop of thread locker will keep it from moving due to vibration, but you can work with the stock screw. Good luck,


Keep the shiny side up!
Scott