EdPDX
09-12-2009, 04:38 PM
I am tuning my carb on my 73 C20. It is a replacement carb- Edelbrock 1406. I tuned it to the previous engine 2 years ago. This year I thought I'd get around to resetting the idle mixture screws with a vacuum gauge. I started at 850 rpm and was showing initial manifold vacuum of 16lbs. I brought the screws out by matching half turns until there were no more gains in vacuum. I ended up with 18.5 lbs- maintaining 850rpm all the while. Now I go to give the truck a tune up which calls for 600rpm 4 degrees BTC. Problem is I can bring the idle down to 600 rpm by backing out the idle screw- the one below the carb linkage on the driver's side. How do I get the rpm down?