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Hopefully I'm explaining this correctly. Engine has two holley carbs (model 4160). I had it rebuild with the holley renew kit and now noticed the idle stays around 1400-1500 rpm instead of 800-900 rpm before the rebuild. This occurs at start up, after engine is warm and while driving around. I would give it light throttle when I'm at a stop to see if it would go down but it slightly goes down to 1200 rpm. I attempted to adjust the idle screw and even at the farthest left turn it still idle high. When I turn the screw right it does raise the idle above 1500 rpm. Other than this, the engine runs good.
My questions are:
Can the rebuild process somehow cause this? My mechanic neighbor did the work.
What are some other adjustments?
Will this hurt the motor?
Is the choke fully opening?
was the secondary stop screw correctly adjusted, can only be done with carburetor removed
I will take some pics soon. I don't think there's a choke from what the previous owner told me. I assumed the secondary stop screw is at the bottom since i have to remove the carb?
Yes there is a very small secondary adjustment screw that you can only see or access with the carb removed and upside down.
IIRC both the primary and secondary throttle shafts should be adjusted initially to expose only .020" of their transfer slots. Then your idle screw would take care of the rest.
I am assuming you either have a huge vacuum leak, the choke is hanging open, or, the rear blades are too far open.
Last edited by leigh1322; Feb 14, 2020 at 09:16 PM.
Yes there is a very small secondary adjustment screw that you can only see or access with the carb removed and upside down.
IIRC both the primary and secondary throttle shafts should be adjusted initially to expose only .020" of their transfer slots. Then your idle screw would take care of the rest.
I am assuming you either have a huge vacuum leak, the choke is hanging open, or, the rear blades are too far open.
Thanks for the info.
So I went out for a quick drive and discovered a strange thing. With light throttle, in an attempt to bring the rpm down, it still dropped down to 1500 rpm. But I decided to give it a heavier throttle and the rpm dropped to 1000 rpm. This was while it was idling and rolling in neutral.
I tried the two different throttle pressure a couple of times and it produced the same results. Definitely not a fix but at least temporarily for now. Any explanation to this?
Sounds like choke to me. Make sure it is warm and the blade is straight up and down. 1200 is about right for a cold fast idle. Somewhere there should be a pic of the choke cam on the pass side. It should fall all the way down when warm. Even without a pic you should be able to figure it out. Choke rod down, cam up, throttle won't close all the way. Assuming you have an early year with a choke coil not a heater pipe or electric coil.
Here's a good explanation of how to adjust all the different kinds of chokes. You do have to adjust it on the car and get a certain rpm at a certain step on the cam. You can do it on a hot or cold engine.That's all there is to it. https://www.chevelles.com/techref/Ad...tic_Chokes.htm
Ok
now we know you have 2 holleys, and no choke.
This makes the throttle adjustments even more important. See this link and this pics.
Basically all 4 throttles should be open the same amount at idle. If it idled well at 800 before it can do it again.
Just going off your description of heavy throttle and letting of, the idle drops. Makes me wonder if it is not the throttle linkage, since the spring force pulling the plates shut would be lower at light throttle than at high throttle when the spring is wound higher giving a greater rotational torque to pull the plates shut. Maybe do a quick check for any binding. Worth checking as it matches your description of events.
Wanted to give an update in case it might help someone else.
Turned out the carbs needed a stronger throttle return spring. She's running smooth and idle is consistent. Thanks to this forum!!
Good job.......I see you have a 1 to 1 linkage and that is good too......BUT.......the front and rear carbs MUST be sync'd together perfect like a motorcycle.
To do this.....loosen the linkage rod......turn both idle screws out completely to close both blades......tighten the linkage rod back up and ease up on both idle screws together a little at a time until you have the desired idle.
The front and rear need to work together as a team.......if the linkage is off....one carb can fight the other and this is where 90% of street tunnel ram problem start. It improves the drivabilty quite a bit around town.
Holley 4160 idle issues
