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Default Question about tuning a carb on a small block Chevy with vacuum gauge

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Old Jan 21, 2016 | 11:12 AM
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crystal383's Avatar
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Default Question about tuning a carb on a small block Chevy with vacuum gauge

I hooked a long vacuum hose up to my carb and ran it into the car so I can see the vacuum gauge while driving so I can find the right jet size.

While driving and pushing the throttle half to 3/4 the vacuum increases up to about 18 in, then when I go wide open throttle the vacuum falls off all of a sudden down to about 4 in . Is that normal?
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Old Jan 21, 2016 | 11:27 AM
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From: Central PA
Car: 1990 IROC
Engine: Rebuilt L98 with H/C/I/Carb
Transmission: TH350 with ATI Treemaster
Axle/Gears: 7.5 with 4.10's
Re: Default Question about tuning a carb on a small block Chevy with vacuum gauge

That is normal. The vacuum will drop off as the secondaries open and the motor demands more air.
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Old Jan 21, 2016 | 12:05 PM
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Re: Default Question about tuning a carb on a small block Chevy with vacuum gauge

Oh ok. Thank you for your help.
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