i have a four bbl carb and i have a feeling that only the front butterfly opens when i rev it up.... i know there is such a thing as a vacuum secondary, but i dont know if i need it or if i just dont know wat im doing.... there are two vacuum fittings on the front of the carb that are both plugged.... im sure they have a use.... someone please help me

 

What brand of 4 bbl carb?

 

There's your answer.secondaries won't open up if there isn't any vacuum going to them toopen them up. Don't know the specifics of the vacuum line diagram though.

 

Vac ports on the carb have nothing to do with secondaries opening. The vaccum 2nd control is internal in the carb, it uses airflow velocity through the barrels that generate lower pressure(this is how the carb meters also) to control how/when the 2nd's open. The easiest way to check is take the air cleaner off and look into the carb and snap the throttle while you're looking into it(be careful if you have carb backfire problems) and see if the 2nd's are opening. Usually they can be adjusted by changing a spring that controls pressure on the diaphragm controlling the 2nd's. If you overmanifold/overcarbed the engine then the 2nd's may not open until high rpm, and even then only part way. Also check to make sure that there's nothing keeping the throttle from opening all the way(something physical, bent etc)

 

That is one more reason I like my mechanical secondaries. I KNOW they are opening up when I mash the loud pedal.

 

+1
And I recomend safety glasses just in case.

 

Time for some theory?
http://www.edelbrock.com/automotive/eps_sect1.html
Googled vacuum secondaries edelbrock theory, you could probably get a similar page for what ever brand carb you have.

 

i wish i had my car rite now so i could fix the carb....

 

I can ALWAYS tell when the vacum secondary's open under throttle. Always. The tires brake loose.

 

is it a possibilty that they are stuck... or somethying in them is stuck? i also wanted to make sure its clean inside and out so that the fuel is metering properly.... do i just get a marine fuel treatment or something?