Q-Jet experts

[big83chevy4x4]

i had to take my carb apart to clean it (again ) and i took it apart more than i did before. there was one screw that is infront of the needle and seat and behind the power valve ?? (funky thing with the main metering rods on it. it a retangle shape that needs a special tool (or needle nose pliers ) to get out. i counted the turns out and put it back where it was (i think)

anyway, now its running rich at idle, is this the idle mixture screw? if so, which way do i have to turn it to get it back to where it was?

if not where is the idle mixture setting at?

this carb is really pissing me off. i want to go TBI SOOOOO bad, just no $$$

 

[blazer74]

Thats the ADP adjustable part throtte, holds the primary rods out of the jets for part throttle cruising when the power valve is pulled down by vaccum, prevents lean condition during cruise. 2.5 to 3.5 turns out from seated, depends on your engine requirements. You dont normally mess with that. you have to make small adjustments untill you get it right. The float adjusted to high can cause rich condition. The mixture adj are on the front at the base plate. They may be covered with factory plugs depending on what year the carb is. Retrace your steps on what you did to the carb one at a time. ,Good luck

 

[big83chevy4x4]

it ran fine at all spots till i had to take it apart and clean it, thats the only thing i adjusted. i didn't adjust the float as it was set correctly before. but maybe it is just a little high i also have never touched the mixture screw in the front.

i remember that ADP was 5 turns in from being loose. just now i realized that i should have screwed it all the way in to find out where it was at so that can't screw up the idle mixture?

which screw on the base plate controls what, is it the left controls the left primary and the right controls the right primary? which way do i turn it to lean it up.

i also noticed last night that it doesn't run so rich when its cold out (24 or so), but when its warm out (got to 43 today) it loads up and dies and is a bitch to start. so i don't think its too far off.

i don't want to screw this carb up too much, thats why im asking before i start turning things.

 

[R72K5]

you should not have removed that thing

not good,

its preset factory setting

 

[pauly383]

Thats why the original castings don't have a plug . I have a removable plug added to mine , I barely , just a SCH , moved it . I wrote down how far too

 

[big83chevy4x4]

now someone tells me

there was a bit of dirt behind it, and i think thats what caused the problem i was having thats it not doing anymore.

 

[big83chevy4x4]

anyone else? didn't get a chance to work on it today, but i am going to mess with it tomorrow

 

[boz42]

there is a book by doug roe. i think it is titled rochester, any how i hav3e it & it is great, lots of pics & reaaly good info covers a complete build & good mods to help it out. it is an essential if u are not well versed on q-jets

 

[big83chevy4x4]

ill have to look for that book. didn't know there was a book on these.

I think i found my problem. it was that adjustment.

Here, Chris points out the power piston stop. Under most conditions, you DON’T want to adjust this stop. If you do move it, be sure to count the turns so you can turn it back. Lowering it will give you less fuel; raising it will increase the fuel to your engine.

http://www.corvettefever.com/howto/53360/

im gonna turn it 1/2 turn down and see what it does, then 1/4 turn either way depending on what is needed.

god i love the internet

 

[blazer74]

You can knock the plug out of the top above the apt and adjust it while running.
Make a tool out of small metal tubing by crushing it to fit the apt. Or go to a good auto parts store and ask for a double D carb adjusing tool, if they know what it is. This will fit the apt. You can buy a flush allen screw plug, I forget if its 3/8 or 5/16 fine thread and tap hole the where the plug was just enough to where the plug fits flush to the top. The plug has to be knock out from the bottom. But if you mess up the top of the carb, your done.

 

[big83chevy4x4]

sweet, did not know about that plug. i will look into doing that. keeps from pulling the carb apart.

thanks abunch, youve been helpfull