Rebuilt 2100 Carb on 302 - Engine is racing

[Owney]

I did a complete rebuild a 2100 carb because it was badly leaking and very dirty. Now it’s all back together but the engine seems to be running rich and when the choke opens the engine starts to race. I can keep it idling if I hold the choke closed While I try to tinker with it.

- I’ve tried adjusting the mixing screws. But at higher RPM it has no effect
- I’ve pulled the idle adjustment back to 0.
- I don’t think it’s the float (could that cause this type of issue?)
- the jets are 49

I just can’t figure what is causing it to race. It will roll up to about 2500 RPM.

Any help would be appreciated.

Jason
Portland, OR
1970 302 4-speed

 

[jckkys]

There's only one reason the engine would be racing. The throttle is open. Now you have to find out what's holing it open. The instructions in the rebuilding kit tell you all the set up steps. These include the choke set up and the curb idle. One of these is likely what's holding the throttle open. Another place to look is the throttle linkage including the accelerator pump linkage to see if something's hanging up.

 

[youngun]

Shine a flashlight down into the carb and you will probably see the throttle plates open. These need to be closed for the carb to run in it's idle circuit.

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[EPB72]

Assuming the throttle is ok and is closed ...did you disconnect your PCV or brake booster vacuum supply line if equipped maybe left off,,or any other large vacuum leak carb base gaskets..???

 

[Rightpace]

The "mixing screws" are only for idle mixture.
Fuel metering is performed by main jet size.
If choke is on then the idle increases due to throttle opening by choke linkage, this will increase fuel input draw by decreasing air intake. If it won't idle normally run your idle mixture screws in to stop and loosen back out two turns. The float is probably misadjusted low, starving for fuel at idle. Remove top and check fuel level in bowl and adjust float.

 

[jckkys]

The jets don't get involved till the throttle plates open past most of the transfer slots. At idle, the jets provide more fuel than the idle circuit can use the idle A/F mixture wouldn't change if the jets were removed. Idle fuel is metered by the idle feed restrictors. In 2100s these are at the bottom of the small tubes under the booster venturi clusters. Float level has little to do with how much fuel passes through them.
Vacuum leaks add air but no fuel so the won't race as the result of vacuum leaks. The lean mixture would make the engine shudder. Read Holley Carburetors & Manifolds from HP Books. Holleys are very similar to Ford carbs especially the 4010 models. This book explains the carb. circuits their functions and interactions.
The OP's symptoms indicate the throttle isn't closing.

 

[Rightpace]

"Now it’s all back together but the engine seems to be running rich and when the choke opens the engine starts to race. I can keep it idling if I hold the choke closed While I try to tinker with it. "
Seems there is more fuel input than needed, so opening the choke introduces more air past the throttle valves, which speeds up the engine.

 

[Rightpace]

Be sure to check out the booster venturi for check-ball and weight installation under screw. I think fuel can dribble out with high float condition if stuck open.