Carb mixture setting

[stangsally]

Have 351w that has been one performanced out, 300 on motor with new 750 holley mech. Want to know if there is a tool that will give you the proper mixture settings. I know i was running to rich at some point, at idle at operating temp. i could see black smoke comming from my turn downs while idling and your eyes would water just standing behind the car, but since i have turned the mixtur screws out about a whole turn at idle now the smoke is gone but i don't want to run it to lean either running 11 1/2 --1 ratio so far i have no pinging or after run on acceleration or shut -off. rich is better than lean. Would hate to loose a $9000 motor due to wrong mixture setting. Would u advise just keep checking the plugs on each run to see if she is running to lean or to rich?.

[~The Jester~]

You hit the nail on the head. Learn how to read the plugs the correct way, and you'll be just fine. Other than that, you can get an aftermarkey air/fuel ratio gauge. It has it's own O2 sensor, and reads your exhaust mixture for you. Summit and Jeg's both carry them, if you want to go that route. Keep in mind also, that just about as soon as you crack the throttle, your now on the main circuit, and those idle adjuster screws do NOTHING. Another point to mention about most idle circuits. The scews do not adjust the mixture ratio. The air/fuel ratio is predetermined in the carb by the idle circuit air bleeds, and the idle fuel well. What the screws DO adjust is the AMOUNT of that predetermined mixture gets fed into your engine. So you're doing it right, just keep checking on it.

Good luck!

[PKRWUD]

1) Gently turn both mixture screws in until they bottom out.
2) Back them both out 1 1/2 turns.
3) Warm up engine
4) Turn idle speed down as LOW as the engine will maintain.
5) Adjust the screws in two round trips (adjust one side, then the other, then come back to the first side, then go back to the other side) to get the highest RPM***.
6) Add an aditional 1/8 turn out for each screw.
7) Reset idle speed to desired level.
8) Shut off engine and check that both screws are the same. If they're not, set both to the average of the two.
9) Restart engine to check idle quality.

***If it's easier for you, attach a vacuum gauge to a manifold vacuum source, and adjust for the highest vacuum reading, rather than the highest RPM.

Take care,
-Chris

[Rev]

What you want after a WOT run at the drag strip, or else where, is a light tan or gray color to the plug electrode insulator. Just kill the engine after a WOT run and coast to a stop. Pull the plugs and examine them. If you have decent fuel mixture distribution, they should all be simiar in color. You'll need to change jets in the carb to alter the WOT fuel/air mixture.

Rev

[canukracer]

Sounds To Me Your Power Valve Is Wrong, It Will Make It Very Rich At An Idle, And Load Up.you Need To Check The Engine Vacuum Reading And Get A Power Valve That Is Lower Than Your Reading

[Ieatcamaros]

It could be the wrong heat range of spark plug too. It probably isn't, but I thought I'd throw that in there.

[canukracer]

Don't Forget Them Float Levels Push On Car For Front, Rear Gas Should Come Out Easy On Rear Wrong Float Level Will Cause Dripping At Venturis At Idle Also Make Sure Secondry Plate Is Closed At Idle This Can Also Pull Fuel Out.