I have a new Holly 4160 with an electric choke that I put on my tired 390 and it started great with a high idle somewhere near 1,300 rpm's and then I would kick it down and go.

When I put in a freshly rebuilt 390 with a 268 cam I put the same carb back on it without touching the settings and cannot seem to get it to idle up over 1,000 rpm's on high idle.

Is there something about the more aggressive cam that requires me to adjust the high idle setting?

 

I don't know for sure, but might have to do with the vacuum, or lack of with the new cam. I know that the electric choke on a Holley has a vacuum port on where it mounts to the main body of the carb. The way I understand it is the vacuum port is there to draw air over the bi-metal coil in the choke. So maybe less air has the coil expanded more and less choke??? Maybe the choke needs to be adjusted for this? Or maybe hook up an external vacuum port the way it is done on a 4160? I feel like my electric chokes never seem to work right even when carb is new too. Maybe it's because I always have bigger cams?

 

I wondered if the reduced vacuum had anything to do with it. The manual for the carb does not say.

 

The fast idle should be acting the same way. Does the engine run fine otherwise?

 

Runs great otherwise. The only other thought I had was maybe with this motor I don't need to tap the go pedal before I hit the starter?

 

Just tighten the choke up a notch and see if that fixes it, if it doesn't make sure the high idle screw sits on the tall part of the choke cam and if it is just turn the high idle screw in until you get the setting you want. If it is sitting in the middle on the cam then tighten it up a little more. It can be kind of a pain to get to the high idle screw sometimes as its not real accessible with the carb on the engine... Just don't turn it so far that the choke closes completely

 

I adjusted it a little and it helped. I need to take it a little farther. It does help if you have your son hold a mirror so that you can see the darn screw.