I just rebuilt my 2 barrel on the 360 and it idles high.

68 FE 360 with Motorcraft 2100 Carb

I had 2 carbs and the mixture screw on one snapped off leaving part of it in the carb. I brought the good base and all the parts from both carbs to be cleaned in a sonic cleaner.
1 carb is what was on it when I got it (tag states 73 Bronco)
2nd carb had no tag but I think it was also from the 70's, maybe 74-75 as I think it came off a motor I acquired from a truck of that year.

I do not remember if the guts I used were for the correct base. I do not know if the butterflies used went to the correct butterfly shaft. Does that make a huge difference?

I also noticed the main butterflies did not seat all the way when put back together but when it's on the motor, looking down into it, it seems to be seated.

All the adjustment screws are backed out all the way. The main idle screw for the butterflies is not even touching the lever. I have it set so if everything was correct it would not idle and just stall out.

The idle is high and on a flat the truck will slowly idle it's way to 30mph.
It also back fires through the exhaust when turned off sometimes. I played with the timing to bring the idle down a bit in hopes of not over reving the motor.
I think the timing is off also because when I do press the peddle to the floor it takes a while to get to 40. Is that normal for a 360? I haven't driven this truck in a while. Put maybe 100 miles on it last summer and was maybe 2-3 years before that it was last on the road.

Input appreciated

Am I going to be looking for a new carb or swapping out parts (butterflies come to mind)?

Thank you

 

Maybe it's a vacuum leak somewhere. A hose could have cracked during removal or installation.

I seem to recall that butterflies have an orientation. If they are installed wrong way round (if vertical, top and bottom cannot be reversed) they won't work. Also, as the butterfly holes can be a loose fit, sometimes a plate gets tightened too much to the left or right and the throttle won't close properly.

Not sure if your carb uses them, but were the nylon bushings for the throttle shaft in good shape?

As an aside, (also not sure about your carb), but it's typical for the butterfly to shaft screws to have the threaded ends peened a bit after installation so the screws can't come out and drop into the engine.

 

Idle is same with or w/o vaccum hooked up.

No nylon bushings that I could see. Where the butterfly shaft is it is tight with no play.
The butterflies are sandwitched in the centershaft. They only go in one way as there are stops in the butterfly plates. I could have put them in upside down but with them being round I can't see where that will make a difference.

 

Flipped the butterflies over and idle problem is now fixed.

But now the exhaust bolts are loosening up.

 

Get some ramp lock bolts from ARRP.