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1970 Firebird Formula 400 - Air-fuel Mixture Starting Point?

Taint3d

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Hey there, I inherited my dad's 1970 Firebird Formula 400 RAM air 3, and I’ve got it running pretty well after sitting for 30+years.

But I have some questions about tuning the air-fuel mixture screws properly on my original quadrajet carb.

I’ve got both screws out 2.5 turns, and it seems to be running okay, but I lose a lot of responsiveness off the line.

Any tips or tricks would be much appreciated, I love this car and would like to have it running as good as possible with spending crazy money.

Thanks everyone!
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Taint3d

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When was the carb rebuilt?

Thank you,
PTA Staff
I rebuilt the carb 3 months ago.

I did fuel pump/water pump/timing chain cover/valve cover gaskets/engine oil/trans fluid/spark plugs/new electronic distributor/trans pan gasket/new starter and a few other things since I got it.

I am a newbie so forgive me if this seems like an elementary problem.

Thank you.
 
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Taint3d

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I rebuilt the carb 3 months ago.

I did fuel pump/water pump/timing chain cover/valve cover gaskets/engine oil/trans fluid/spark plugs/new electronic distributor/trans pan gasket/new starter and a few other things since I got it.

I am a newbie so forgive me if this seems like an elementary problem.

Thank you.
I did a full rebuild kit on the carb soaked it in carb cleaner.

The vacuum seems good after I changed the primary vacuum diaphragm.

Did new needle/seat/jets and accelerator pump. I’ve got a vacuum gauge and I guess my question is where to start tuning?

I’ve watched all the YouTube videos but nobody really explains how many turns out on the air-fuel mixture screws to start and how to tell when you are getting closer?

Thank you
 
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Pontiac Trans Am

Smokey
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What is the read on the vacuum gauge?

15-20PSI?

Start at 4, turns out, and watch the gauge move up to the highest vacuum.

Do one side at a time.

Also, make sure the choke is fully opening when warmed up.

After setting idle screws, make sure the float level is set correctly.

We hope that helps.

Thank you,
PTA Staff
 

Taint3d

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What is the read on the vacuum gauge?

15-20PSI?

Start at 4, turns out, and watch the gauge move up to the highest vacuum.

Do one side at a time.

Also, make sure the choke is fully opening when warmed up.

After setting idle screws, make sure the float level is set correctly.

We hope that helps.

Thank you,
PTA Staff
The vacuum is about 19 psi at the Moment.

Thank you!

I’ll try this.
 
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Taint3d

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Ok great!

Thank you so much.

I’ll go through this today and report back.

Ok, so first of all, I double-checked my timing, and I believe this was my biggest issue.

I had initially set it at 9 degrees according to the vehicle's spec, but it seems the distributor has slipped, and it was at like 15.

So I reset that to spec, and it seems like my issue was immediately better.

Then I started to tune the carb. First, the vacuum was not at 19. It was 14 psi, turned the screws to 4 full turns to start, and landed on 3.25 turns on the left screw and 2.5 on the right.

PSI ended up at about 15 psi when I was done.

She seems to be running much better now, probably mainly from the timing adjustment but either way, thank you!
 
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