quasdrajet 4 barrel won't open no more

85 chevy truck with 305 and quadrajet 4 barrel, all of a sudden the 4 barrel doesn't seem to be opening at all, flooring it at 55 mph and it barely goes, vaccuum lines seem fine, i don't know the name of the component that opens it but vaccuum pressure seems to increase ok when the throttle is pulled by hand, any help appreciated thanks

make sure the choke linkage is out of the way. if the choke is on, 4bbls wont open. make sure nothing else is obstructing it too.

When you say "4Barrell wont open" you mean the large secondary's right? Try checking the secondary lockout lever and/or the vaccum break diaphram. Unlike a mechanical secondary (double pumper), the vacumm type secondary's are not directly connected to primary linkage.In the old school days guys used to get diaphram spring assortments and put in weaker spring, thus allowing less engine vacumm t open the spreadbore. But not too much to where u get a flat spot when floored.

It is probably the choke linkage lockout lever, as others say here. Check to make sure your choke is working properly. Allow the engine to warm up and then look at the choke. It should be absolutely straight up and wide open. If the choke is not opening all the way, then the lockout lever prevents the secondaries from opening. This is designed to prevent you from over-accelerating a cold engine.

get an edelbrock lol

o by the way, i thought engines LOST vaccum as rpm's increased. this is what the dude that sold me a different powervalve for my holley carb told me. he sold me one that opens at 4.5 inches of vaccum to replace the one that opened at 6 inches.
it really helped out with not bogging down from too much fuel too soon. im confused. can someone clarify the vaccum thing?

o by the way, i thought engines LOST vaccum as rpm's increased. this is what the dude that sold me a different powervalve for my holley carb told me. he sold me one that opens at 4.5 inches of vaccum to replace the one that opened at 6 inches.
it really helped out with not bogging down from too much fuel too soon. im confused. can someone clarify the vaccum thing?


At idle vacuum is about 15-20 hg, at the midrange (approx 2500rpm) it's about 19-24 hg then at WOT (wide open throttle) is nearly 0 hg. So in a way your right about decreased vacuum when engine load increases.

When you say "4Barrell wont open" you mean the large secondary's right? Try checking the secondary lockout lever and/or the vaccum break diaphram. Unlike a mechanical secondary (double pumper), the vacumm type secondary's are not directly connected to primary linkage.In the old school days guys used to get diaphram spring assortments and put in weaker spring, thus allowing less engine vacumm t open the spreadbore. But not too much to where u get a flat spot when floored.my choke is manual and it is opening all the way, the secondary's linkage is connected to a component that pullls in at start up and idle, even if that component was to push out, it wouldn't open the secondaries( even if I push it by hand),the vacuum does increase as I pull on the throttle. is there a way to see if they open while in park with the hood up? thanks

yeah lol just drop a screw in one of the secondary barrels and see if it goes into the engine lol jk that a very bad thing to do lol