idle decreasing

[Overlord]

My idle keeps decreasing. I set it to 650 rpm and when I go for a drive, at the 2nd or 3rd stop the idle drops to about 500-550 rpm. My vacuum is at a steady 22 in/Hg, timing set at 7* btdc, spark pugs/wires/cap/rotor are about 2.5 years old. The carb was rebuilt by Jim C, along with a dizzy recurve also 2.5 years ago. It's desmoged btw. Any thoughts?

 

[inkpot]

Howdy! Are you adjusting the cold idle screw or the hot idle screw? John

 

[Overlord]

Howdy! Are you adjusting the cold idle screw or the hot idle screw? John

Do you mean the slow and fast?

 

[inkpot]

Do you mean the slow and fast?

There is one idle screw on the choke linkage that adjusts engine speed only when the engine is cold enough for the choke to be engaged. There is another idle screw that adjusts the engine speed when fully warmed up. Then there is an idle mix screw that MAY change idle speed when adjusted, but you don't want to do that!! John

 

[Overlord]

I adjusted the "idle speed adjusting screw"

 

[inkpot]

I adjusted the "idle speed adjusting screw"

View attachment 230034

Howdy! That should be the right one. I'm guessing your doing this with the engine warmed up good, and the air cleaner on. Do you feel any resistance or tightness on that screw when you turn it. It is spring loaded to hold it in position, like a lockwasher. If it is really loose, then it may have a worn out spring which would let the screw move at will. John