On my truck I have a 302 engine with a 600 Holley. Everything is hooked up and the floats have been adjusted. I haven't, however, been able to fine tune anything because the idle will not go below 1600 rpm. It's like it is staying on high idle. The idle adjustment screw is turned out and so is the high idle screw behind the electric choke. Any thoughts on how I can get it to idle like it's supposed to?

 

First check for places air can get into the engine. Double check all the vacuum ports and vacuum lines, and double check the gasket underneath the carb.

If you are confident there is no air coming in somewhere else, the first thing I would do is go over to the pass side of the carb, on the secondary underneath the secondary diapraghm, and loosen that phillips screw to let the linkage relax and then tighten it. See if that makes a difference.

Is this a brand new carb or a used carb? Has it been rebuilt by you or someone else?

 

Well if you are sure both the idle speed screw and the choke fast idle screw are not hitting the stops I can only see it being 3 things
1- Disconnect the throttle and if it has it trany linkage from the carb and see if it idles.
2- A vacuum leak
3- Bent throttle blades


If the linkage disconnected did not lower it with the motor running at idle take your hand and start covering the carb and see what happens the more it is covered?


The other thing is pull the carb and with the blades closed how much of the idle slot do you see? Should only see a little hole not a slot.
Dave ----

 

Well it is a new carb so I shouldn't have to worry about bent blades. I have disconnected both the throttle and the trans kickdown. Both screws are backed out.
Still just idles at about1,649

 

DO make sure the choke high idle cam has fully retracted. Other than that the suggestions provided should fix ya up.

 

Yep recheck the choke cam to make sure that is not hanging up.
Then look for a BIG vacuum leak. At the base of the carb it may have a port for PCV hose if no hose make sure it is capped and if capped that it is not cracked. also check for any other hoses that may have been knocked off.

You did not post what intake you are using on this motor. Is it stock or after market?
Dave ----

 

If this is a new carb, you have air getting in from somewhere. Take the carb off and hold it up high and put the gasket on it underneath and see if it covers everything. If you are using the factory spacer plate, it usually has a very large vacuum port on the back, make sure you are using it or it's plugged off.

 

Also make sure the secondary stop adjustment didn't get cranked way in by somebody... Been there done that.

 

It is a Weiand Dual Plane Street Warrior intake that I am using. I simply cannot find any vacuum leaks as far as the gasket leaking. I have hoses either hooked up or connectors plugged. I will try and make sure that there aren't any holes in the hoses, but I have checked recently and found that all hoses were good. I have the floats adjusted but not the idle mixture screws for obvious reasons. It is smoking some but not much. He secondary screw is backed out and the choke cam is relaxed all the way. The engine has great throttle response, it just obviously will not physically go below like 1600 rpm or so.


ALSO, on another note, I have the AOD kickdown hooked up correctly and adjusted correctly, but the cable itself has a lot of resistance. I took the cable loose from the throttle and just pulled it by hand and it seems to have a LOT of resistance. It's enough to pop my cable stop for the throttle cable off of the cable. Any thoughts as far as that goes??

 

Has the motor been rebuilt?
I ask because if rebuilt and the block decked & heads milled it can throw off the angle between heads & intake. It could also happen if not rebuilt.
This poor sealing could be at the bottom of heads and intake, making a vacuum leak inside the motor and hard to find.


You did say "it is smoking some" this could be a sign of a vacuum leak from inside the motor lifter valley area as it is pulling in oil.
Dave ----

 

Well it has not been rebuilt. It was an efi motor converted to efi. I was careful putting the intake in and everything. Made sure the surfaces on the heads were exceptionally clean and I used silicone on the block where leaks can usually form. Also, the smoke is black smoke from incorrect air/fuel ratio I believe

 

Ok on the black smoke when you said smoke I was thinking oil.


Even with the sealing flanges clean for a good seal if say the heads are at 25* and the intake at 35* that is a 10* gap left someplace that air/vacuum can get in causing a leak.


Do you have another carb to try to see if it is the carb?
I had an older Holley 600 that had an internal vacuum leak even after rebuilding. I replaced the carb and all was good don't know why the other had a vacuum leak?


Have you tried to cover / choke off the carb when running to see what happens?
Dave ----

 

I actually had a different carb on before, an edelbrock 600. It was actually corroded pretty bad on the inside though so we bought this Holley 600. It didn't run well enough with the bad carb before to be able to tell.

 

Your not helping me help you
I am at a lost now why it will not idle down.


This carb have vacuum secondaries? If so disconnect the linkage to it and see if that helps.
Dave ----

 

Haha Dave yes this has been extremely frustrating. I have had people help me with it who have worked with these carbs before and they are stumped too. I haven't disconnected the secondary linkage but it is completely relaxed. I can move it all over the place. Ther is no resistance. I actually hadn't tried putting my hand right over it. The closest I got to that was just having the choke all the way shut. When you put it in gear it goes down to the right idle speed but
It slowly, very slowly, trickles down from that idle speed to lower and lower rpm until it almost dies