Tuning 600cfm holley for 305 engine input needed.

[Project69]

My friend has a factory 305 engine in his 78 Camaro, headers, holley dual plane and 2.5" exhaust all the way back are the only mods. Car has only 35k miles (grandmas old car)

I installed the 600 and its running pig rich, tried adjusting the carb but still runs rich. Thinking 600 is way to big for this thing. Could I do a jet swap on it? Budget is low and its his daily so trying to keep from spending an arm and a leg.

Thanks

[Shaker455]

Start off by keeping this very simple and do one adjustement at a time.

1) Remove the carb and set the front and rear throttle blades evenly.
More than likely the front is up too far on the transfer slot and causing the rich condition.

2) Set both idle mixture screws to 1-1/2 turns out to get the car fired.

3) Adjust idle stop screws for desired rpm in park

4) Use a vacuum gauge and set for best vacuum keeping mix screws even.

[Vegas69]

I agree with Shaker. Also, adjust the idle mixture screws to max vaccum or rpm. (Vaccum is better) A little more ignition advance will also help. If it's fat at cruise or in the secondary, I'd drop the jets 4 sizes at a time.

[TheJDMan]

A 600cfm is a SMALL carb and is definately not too big. Check the items mentioned above but most likely you will need a jet change and/or power valve change. This will also give you the opportunity to replace float bowl and metering block gaskets.

[ROBS6T8]

Old thread, but what vacuum source would you use for the tuning? QFT 650 is my carb. Thanks.
Maybe the brake booster port?

[andrewb70]

Old thread, but what vacuum source would you use for the tuning? QFT 650 is my carb. Thanks.
Maybe the brake booster port?

Any manifold vacuum (below the throttle blades) source is acceptable.

Andrew

[ROBS6T8]

Thanks. I just wasn't sure about the one used for the VA. Screw everything up!