carburetor

[3r!c84]

how do i know if my back flaps are opening when i floor it?it dont seem to be opening/

[85Bowtie]

It depends, what kind of carb do you have? New? Used? Vacuum or Mechanical?

Usually there is a "kick" when the secondaries open, however, that's also a sign of a deadspot which isn't a big deal but is a pain to get rid off.

If anything, you should feel somewhat of a resurgance in power, in other words, it gets noticeably faster.

On my Diplomat cop car, I can "hear" it open, you can't rev that high on only the first 2 barrels that quickly when you nail it.

If you can't feel a "kick" and your carb runs good, then you have it tuned right and you shouldn't worry.


What makes you think they aren't opening?

[73chevyman]

if you have a stock aircleaner flip the lid you'll hear them. like a sudden rush of air. also check to see if your linkage is working with the truck off you'll see them open up. jack

[3r!c84]

its the stock carb.roghester quadrajet .it has a knn air filter,and i dont feel it open it realy lags when u floor it

[enaberif]

Originally Posted by 3r!c84

its the stock carb.roghester quadrajet .it has a knn air filter,and i dont feel it open it realy lags when u floor it

Lag is another issue.

But with my 4" open air filter when all 4 are open I can physically hear the engine tone change and it makes me giggle like a school kid

[85Bowtie]

Originally Posted by 3r!c84

its the stock carb.roghester quadrajet .it has a knn air filter,and i dont feel it open it realy lags when u floor it

There's your problem.

Ditch the quadrajunk and get a Holley or Edelbrock.

Some people will tell you Q-Jets are great but I've never had any luck with them. They're tempermental carbs and a PITA to rebuild IMO.

You could play expert mechanic and learn the tricks and how-to's of the Q-Jet. Or, you could save time and enjoy driving your truck more often by just switching to an Edelbrock.

[OrangeAnimal]

I can build the quadrajet carb to be a amazing carb but it does take alot of work and a good core to use which is getting harder to find at the junk yards. I would suggest using a Edelbrock. I do not care for Holley on a street driven truck. I really haven't had much luck with them. They take alot of work to tune and although it's worth it in the end they are more for getting max power out of a engine and not so good with fuel mileage.

My .02 cents. Good luck.

[85Bowtie]

I'm the opposite, I can tune/rebuild any Holley/Edelbrock/Carter even the thermoquad.

I've got a Holley 870 on my 440 that runs fine on the street or track, doesn't even run slightly rich.

Everything else I use Edelbrock.

The Q-Jet is a Pandora's Box I am unwilling to open.

[3r!c84]

yea im thinking about a new carb.but idk if a Vacuum line or something is rong?

on the passinger side under the choke there is a retaner thing that hold the back flap from opening?
but when i move that with my finder and floor it the back flaps open?
idk if that retaner thing moves my vacuum or what? I've looked all around that thing and cant find out how that thing opens?

[PhilaTruck]

Sounds like a bad accelerator pump or a clogged fuel filter. Both cheap & easy to check.

[powerdriver 1958]

there is a little spring adjustment on the secondary throttle valve that causes the bog most times

[3r!c84]

Originally Posted by PhilaTruck

Sounds like a bad accelerator pump or a clogged fuel filter. Both cheap & easy to check.

what is a accelerator pump and where is it at?

[sierra4x4]

I always rip off the link that is on the pass. side above the choke housing that goes back to the secondaries on the top. Those things almost always hold the secondaries closed.

I hope that makes sense.

[3r!c84]

Originally Posted by sierra4x4

I always rip off the link that is on the pass. side above the choke housing that goes back to the secondaries on the top. Those things almost always hold the secondaries closed.

I hope that makes sense.

lol not at all
do u got a pic or somthing

[sierra4x4]

I found a pic of the link that I was talking about.

[PhilaTruck]

I'll assume you have a mostly stock engine?

The accelerator pump is the rod that's activated by the lever on top of the carb (drivers side). You need to remove the top of the carb to replace it.

Also, a dirty carb can also cause poor performance. A rebuilt kit will cost about $20.

Here's a great link to info for tuning your Q-jet. You'll see there's text about 2/3rds down the page referring to the secondary air valve that I think Powerdriver mentioned.

Mike Ervin's & Damon Nickles' excellent Q-jet tuning tips

Here's a link to a parts supplier. carburetion.com

[3r!c84]

ok i understand where its at but what do that rod do?

[3r!c84]

this is not my carb just a pic i found.
the white thing is hiting the green

[3r!c84]

me and my dad talked and im just going to buy a new carb. i allready got a performer intake waiting so ill just save up a lil $ and buy something new

[piecesparts]

Are you absolutely sure that the carb is a Rochester Quadrajet. There is a reason for this question---Carter ALSO made quadrajets and the carter carb has some defiencies in their design. The needles for the secondaries pass through the carb body in openings that tend to errode away and when you accelerate the bogging issue that you described may exist. So to eliminate the bog most drivers would tend to ease through that transition area.

The Rochester carb bodies has a brass insert in that area and did not errode, so the transition from the primaries to the secondaries was better and more prevalent. Also your bogging could be from the surge from your accelerator pump.

[3r!c84]

I am absolutely sure that the carb is a Rochester Quadrajet
it says Rochester Quadrajet
17082226
1612duu

[Pyrotechnic]

Here's the thing, if you have a Quadrajet and the secondaries are opening too soon or not soon enough, and the engine runs good otherwise, switching to a different carb is not the answer. The fact is, the secondary air door on the Quadrajet is easily adjusted to open sooner or later.

[3r!c84]

its not opening at all ,ive been reading up on this carb and they put the same carbs on 305-454s so its way to much cfm for this motor ,thats why the backs are not opening.

[3r!c84]

and if u can adjust it,how would you adjust it?

[OrangeAnimal]

They used Quadrajets of different cfm ratings on 305-454. They are tricky and you have to know exactly what is going on to make it act up.

Another note on your secondaries. They might not open at all when you floor it in park. You need to have load on the engine to make them work properly. If you want to change the carb out then it's not a big deal. There isn't much to it.

Good luck hope it makes a noticeable difference.