high idle dilemma

[str8up720]

I've been trying to figure this one out for some time now. Its a 318 stock except for a cam, headers, edelbrock 4 barrel, and ignition upgrades. When I fire it up, it slowly seems to build up rpms up to around 3,000.fast idle screw is back all the way, so is the idle screw, and idle mixture screw are set at 1 1/2 I have played around with the choke and noticed that the idle calms down when I hold the choke closed. Which as far as I know is the opposite of how the choke should work.. i believe it should be richening up the mixture when the choke is closed to get it running faster, thus warming the engine up quicker. I believe I have come to the theory that I have a vacuum leak, where extra air is getting in and thus the extra fuel ( the richening effect) balances out with that extra air and makes it run "normal". Does this make sense to anyone, or am I just over thinking it? Any input or further ideas would keep me a bit sane..

 

[khryslerkid]

Having a vacuum leak can act just as you discribed. I've used a can of parts cleaner and sprayed around the intake gasket. When it gets sucked in a leaking gasket, the rpms will change suddenly. Carb cleaner works better but it's flammable and if it comes in contact with a bad plug wire or gets up under the dizzy cap, it could start a fire. But you get what I'm saying.
Check all vacuum lines first, remove and plug them one at a time from the manifold. Pull a vacuum on the vacuum advance and see if it holds. Do the same on the brake booster too if you have one. Normally if that's bad, you'll notice it in you braking. Think simple, good luck...

 

[67 coronet]

start the car and cover the air horn(top of carb)with your hand.it should choke out the carb and stall the eng.if not,then you have a vac leak.a motor is just an air pump,starve it for air and it will die.to search for a vac leak a spray bottle with water will do just as good as carb cleaner.no fire that way.you can also unhook each vac powered item and plug with vac cap to check each one.(booster and such)

 

[super-bee_ski]

x2

 

[RS23VOA]

Is the throttle cable adjustment allowing the carb to close all the way? I've seen that happen.

 

[str8up720]

I'm liking the idea of covering up the air horn. I will test out all the lines as well. I'm only running PVC to carb and brake booster to intake. Everything else is plugged up. Advance is mechanical but I already checked the springs and bushing in the mad pro billet. All looked good. So does the linkage. I will play around with the spraying of cleaner or water. How will the rpm react with this method? Increase/decrease?? What areas should I focus on. Around intake, carb...anywhere else?

 

[mopar 3 B]

Are the butterfly's seating in the carb base? If they are hanging up in the bore the carb will not shut down. look in top of carb and see if they are closing all the way. If not loosen screws and adjust. Do not try to take the screws out as they are staked so they will not fall out of the throttle shaft if they become loose.

 

[Xp29h]

Just to throw another one in the mix, I've seen an improperly adjusted kick down rod and return spring. I've seen where it is slightly pulling on throttle lever increasing the rpm to a certain point. Was hard to spot because it was slight.

If non of the above thoughts work, unhook your kick down spring and see what happens. If you don't have the spring, completely disregard! Lol. Good luck