how far do you have your idle screws backed out

put a rebuild proper year uadrajet on my 70 and I thought it was a little rich so I checked them and the y were backed out 1 1/2 turns . I backed them out another turn and I still think they might have to go more .|On my 76 vette I could have sworn that I had them out close to 5 turns. Any comments/

 

Adjust the air/idle mixture screws until you have highest idle speed, or highest vacuum level.

 

So all ihave to do is hook my vacuum gauge to the vaccuum port and adjust the screws and watch the gauge?

 

Yes, and make sure you hook the vacuum gauge to the full time vacuum not the ported vacuum. By the way, Rochester advises that the idle air screws be set to 2 full turns from closed after a rebuild for starters.

 

Just to add to this, a couple of quick refresher links on the topic... Click the different scenarios to watch the vacuum gauge move.. Don't know why but I've had em bookmarked here on the computer... Must have thought they were useful for something...
:3gears:

1. http://www.secondchancegarage.com/public/186.cfm

2. http://www.chevyhiperformance.com/howto/45638/index.html

 

And when you close the needles to start the basic back out,,, close them GENTLY.... In the past I have encountered a bunch of carbs/idle needles that have been destroyed by brute handling....once you score the needle and upset the seat, that carb will never idle right again.....

 

Thanks for the advice , one more thing am I right in assuming that turning the screws out leans the q jet.

 

Just the opposite - IN (CW) is 'lean', OUT (CCW) is 'rich' !! :TU:

 

Wow thanks glad I asked.

 

I always thought you turn them in until the motor starts to slow down. Then turn them a half to a full turn out.

 

That's correct, you do turn them in to slow down the rpm and then, out for max vacuum and idle speed.

 

The strange thing is I did turn them out to the point where they musy have had only one thread holding the screw in and I didn't hear any noticable difference. Maybe my hearing is bad at my age.

 

Maybe you have a vac. Leak at the base of the carb.

 

If things are ''normal'' you should be able to kill the engine by turning the idle screws alone.... each one will kill the engine....

 

Also keep in mind that 1979 and later Q-jets use fine pitch metric threads for the idle mixture screws, and often very tiny holes under them. It often takes 4 or more turns out with the later carburetors to get enough fuel to the engine to fine tune them.

There are also a least half a dozen different idle mixture screws for the early carburetors, with different tip lengths. Most really early carbs have short tips, and big holes under them, so they put a LOT of fuel to the engine without backing them out very far.

Typically, the later the model year, the more conservative the idle fuel delivery, and the mixture screws will have longer tips, with smaller holes under them......Cliff

 

Larry is correct...I had to learn this part, as well. The idle mix screws are metering a combination of fuel and air. That's why the throttle blades at idle are just about completely closed, the air is coming from the air bleeds at the top of the carb. The air is sucked into those bleeds, and the bleeds run next to the tops of the idle tubes which pick up fuel from the primary wells, and the whole mixture goes down the carb to the base plate where it meets the mix screws that feed it into the intake.

When the throttle is depressed, the blades open, and the idle air bleeds shut off and the main system takes over after a transition period.

 

I do have the Cliff Ruggles q jet book , I will look and see if I can determine what is happening. This carb was supposed to be rebuilt to manufacturer specs and is period correct for my year.
So If I look down through my butterflys at idle the throttle plates are supposed to be closed is what I am reading here. If they are and I still can't get the idle screws to effect idle rpm's what is my next step do I need new idle screws?

---------- Post added at 06:20 AM ---------- Previous post was at 06:18 AM ----------

And by the way timing was checked and was supposed to be spot on, I believe 10 degrees advanced.

 

Sorry a little like a Flintstone when it comes to modern Tech. Its a 70 350 automatic, don't know what cam but believe it is stock, hei distributer. Does the negine have to be fully warmed up to set idle , might have been to cold when I was adjusting screws.

Thx