Factory Mixture Settings On 2bl Rochester

I was wondering what the factory set the mixture screws at on a 71 Buick Skylark 350 2bl any help would be great.
thanks
Bill

 

Can anyone help me out? If not factory specs than where you are running them in your car?
thanks

 

I guess this is a tougher question than I thought.

 

Sorry, didn't see this until just now. There isn't a particular setting, each engine/carb is different.

The best way to set them is with a vacuum gauge hooked up to a manifold port:
1. Make SURE your ignition system is good, otherwise you'll go crazy. Timing set, etc.
2. Turn both idle mix screws in *lightly* until they just bottom out.
3. Back them each out 3 turns.
4. Start the engine, warm it up, and set the idle speed to spec (I like 850 rpm warm in neitral)
5. Turn each screw in/out (usually in) to get the highest vacuum reading on the gauge. Go back and forth between them, adjusting for the highest steady vacuum.
6. Turn each screw in just a touch, so that the carb is just on the lean side of the highest vacuum reading. Usually an eighth to a quarter turn.

** Some people leave it at the highest vacuum reading, I go a tad lean for economy. I don't know how big a difference it really makes, though.

Second best way is with a tach, or by ear if you're familiar with your engine. Often called the "Lean Drop" method.
1. Warm engine, good ignition, idle speed set, etc.
2. Turn each screw in/out to get the highest possible idle speed.
3. Readjust the idle speed.
4. Repeat step 2 and 3 just to doublecheck.
5. Turn each screw in (lean) just enough to drop the idle speed 25 rpm, for a total rpm drop of 50rpm.
6. Reset the idle speed back up the 50 rpm.

GM used to recommend the "Lean Drop" method. I think that they're both really doing the same thing, just different ways to measure where you're going.

Hope this helps, if not, let me know! :TU:

 

Thanks I will give this a try when I get home from work.
thanks again
Bill

 

Actually, the correct setting is to maximize the idle speed with the mixture screws, then lean them 10 rpm per screw. Any more than 10 rpm, and the engine will run rough. Usually, the 10 rpm drop method will maximize engine smoothness, but economy as well. Ray

 

Thanks I will give it a try.
Bill

 

Thanks for keeping me honest, Ray :TU:
Shows how long it's been since I haven't used a vacuum gauge, and what happens when you trust my faulty memory :error: ou: :laugh:

 

We're all in this together. No problem. After a while, all of these specs run together for me as well. Ray

 

Going that touch lean at idle will TREMENDOUSLY reduce hydrocarbon emissions, while not affecting idle quality much at all. It's a win/win deal.