HD8s - getting below 1000 rpm idle

[steveg]

After flogging this one for a while, on my slow run valves the magic spot seems to be in the area of 7/8 - 1 turn open. So far this is giving me a 600-800 rpm idle without the car feeling like it's about to die.

The recommended 2-1/4 turns gives the usual 1500 rpm idle.

All this with the throttle stop screws set to "paper thickness" away from the stops.

 

[Keoke]

After flogging this one for a while, on my slow run valves the magic spot seems to be in the area of 7/8 - 1 turn open. So far this is giving me a 600-800 rpm idle without the car feeling like it's about to die.

That is about what I get on a precision RPM gauge,Tach says 1000 RPM.

 

[RAC68]

Great news Steve,

I have often felt that adjusting the HD8s is like playing 3D Chess. Move one adjustment and something else is left open. Change the second thing and something else screws up the idle. Getting an even, steady, lower then 1000 RPM idle is like winning the lottery. When it hits, you are both surprised and elated. So, Congratulations Steve, you just hit the big one.


All the best,
Ray (64BJ8P1)

 

[vette]

Hi Steve, I think I will agree with Ray, but I am determined to believe there is a systemic reason in all this. I have my idle stop screws at a paper thickness away from the stops. I have my slow run screws set at 3 1/2 turns out and the car is idling at 600 to 700 rpms. After running it for about a week with the throttle blades cracked open a touch I found that it was an unstable idle. So I went back to closing the throttle blades completely. The idle is stable but I have found that turning on the headlights or with High beams or with the Lucas driving lights that the draw on the alternator will slow the idle by as much as 2 to 300 rpms. That's quite amazing to me. Since we all are getting rather different results by doing almost the same things I am going to hazzard a guess that there are two variables that we at least have not openly discussed. They are: the jet richness, and the timing. I believe both of those could have a major impact on the Slow Run Screw setting. As time permits I hope to investigate that premise. Dave.

 

[steveg]

Dave,
I think you are right - it's a system and everything is connected. I have adjusted my carbs to rectify the spark plug issues in the other thread, then adjusted my slow run screws with the throttle butterflies closed.