Carb Tuning

302 or 351 in the bronc?

88-GT said:

Hey guys not sure if you will be able to help but I have no expierience tuning carbs and need some help.

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Heres what you do.

Punch some holes in the exhaust, depending on location you'll need one or two.

Get one or two supds and weld over the holes.

Install Ox sensors, get a volt meter, take readings.

Adjust accordingly.




Or

You can learn how to read plugs.

Play with the jetting, take it for a drive, see if you like it, read a plug or two, sniff the exhaust. make a decision.

It's awful Old School ...

Blue Thunder said:

302 or 351 in the bronc?

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its a 2.8

MadMark said:

Play with the jetting, take it for a drive, see if you like it, read a plug or two, sniff the exhaust. make a decision.

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there are 2 screws on the carb could you tell me witch does witch and witch direction give more fuel and witch does less

If it's the 2100/2150 model Autolite there's 2 screws that come out the front near the base underneath the fuel bowl. Go gently all the way in on each screw and then turn back out 2 turns. Adjust from there. Clockwise leans it out, Counter clock wise richens. Both screws do the same thing, one for each venturi. Try to keep them as equal (# of turn) as possible. Idle speed is on the driver's side of the carb at about a 45* angle tward the firewall.

Tuning: With an analog tach
Engine must be a low idle. 600-800rpms is ideal. Adjust each screw CW and CCW(equally) until you get max rpm (engine rpm will fluctuate when adjusting these screws) and then back each screw off 1/4 to 1/2 a turn (Clockwise). Set desired or factory Rpm.

Tuning: With a Vacuum gauge
Attach a vacuum gauge to a 'manifold vacuum' source (anywhere below the throttleplates and anywhere on the intake manifold). Engine must be a low idle. 600-800rpms is ideal. Adjust each screw CW and CCW(equally) until you get max Vacuum (engine rpm and gauge needle will fluctuate when adjusting these screws) and then back each screw off 1/4 to 1/2 a turn (Clockwise) or reduce one inch-lb of vacuum. Set desired or factory Rpm.

88-GT said:

Hey guys not sure if you will be able to help but I have no expierience tuning carbs and need some help.

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What is this 'Carb' to which you refer? I have never heard of such a creature ... What does it do?

What Dano wrote with one addition:


First thing you do is adjust the valves.

Okay, so you bought a Bronco II, not a Bronco. Big difference. You've got a 2.8 V6 and are using the carb off a 302? I'd say that's your first mistake. You'd have better luck using a carb off a V6 than a V8. The mixture screws adjust A/F for idle ONLY, they have nothing to do with part throttle. If the truck won't run well when you try to drive it, you've got other issues than idle mixture.

I agree with Mark (did I just say that??), I would start with the valve adjustment. The 2.8 requires it now and then, and if it was never done, it could run like a pail.