c4 modulator vacuum routing
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Joined: Mar 2006
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c4 modulator vacuum routing
any one know where the vacuum lines on the mod. go too. there is two of them.its a 73 with a holley. if it was one it would be a no-brainer to me but its got two. please help!
New User
Joined: Apr 2006
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The modulator gets its vacuum from the intake manifold from under the throttle plate . What it does is as vacuum changes under differant loads it controls the shift points. The other vacuum port on the holley in the metering block is ported vacuum and that is above the throttle plate and only has vacuum to it as the throttle opens . It is usally for the advance on the distributor. hope this helps.
Senior User
Joined: Oct 2001
Posts: 258
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From: Central Virginia
I think your talking about to two ports on the mod. valve. Just use the outer one (larger tube) and leave the other one open. That one was hooked to the EGR valve back in 73 but there's no need to run that one.
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