I have just converted my 351 2bbl to a 4bbl. When I start the car, it does not go to an idle. I sounds like the engine is floored. Even when I have the idle turned all the way down the engine is still at a extremely high RPM. Does anyone have any suggestions?

 

hmmm im thinking you might need to tune the engine down a few degrees...which way i dont know.....

but if the last carb idled fine.....im guessing its not the engine and just the carb......it could be a bad air/ fuel mixture....

theres my two cents

 

what 4bbl is it ?
if your timing is right, then:
check the linkage to make sure the pedal doesn't already accelerate in idle (too long linkage).

are you talking hot or cold ? if only in cold adjust the choke. If in hot make sure the choke plate is fully open and the fast idle screw doesn't increase your rpms. you can adjust idle mixture with screws which will change the rpms, but you need to make sure that the accelerator plate (don't know what it's called. the plate under the choke plate) is adjusted as well. again this is done with a screw normally.

 

Check the throttle linkage when the engine is off to see if it is the right length. If it is, then check to see if the secondaries are hanging up on the intake.

 

+1 on the throttle linkage, also may want to check your fast idle screw. However I don't know if it can even idle that fast.

 

There is an adjustment screw for the secondary throttle plate.Its a very small screw and hard to get at but its on the passenger side near the bottom.this screw can allow you to open the secondaries up slightly for racing engines.Instead of drilling holes in the primary plates.(Holley 4160 vac sec).quoted from the holley carburetor book "when a high overlap cam is used it may be necessary to drill holes in thethrottle plates to increase airflow at idle.This allows the throttle plates to remain properly positioned with relation to the transfer slot improving idle characteristics and prevent plug fouling." You may want to remove the carb to find it and adjust it if necessary.Is it a used carb?Check if previous user hasnt drilled these holes in the primary plates.
I tried improving my idle by opening these plates but it did me no good.

 

Intake leaking from one of the gaskets? That will cause it to rev high.

 

same thing happened to me and it was because the throttle linkage was hooked up...

 

+1 on the linkage , I would disconnect the linkage and troubleshoot it from there, at least that would eliminate the linkage from the equation. Then lower the idle, if still high, check for vacuum leaks, but I think your going to find a carb related problem.

 

oh and is it a new or used carburator and what cfm? if its used it might just be a piece of crap or need to be rebuilt