General Category > Quadrajet Carb Talk and Tips

Idle Channel Restrictions

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Greasy Harley:
I could use a little help. I'm working on a Q-jet off a '79 k10 w/ a 350 #17059201

Going through following the "First Recipe For Success" and carefully measuring and re-calibrating everything ( I hope)
The spec in the book shows the Idle channel restrictions should be .046 and idle tubes should be .036
My idle tubes measured .023 no problem, I can drill those out (also Cliff sent me brand new ones)

Problem is, my idle channel restrictions are already .052

Is this going to be a major problem? can this be rectified?

It was running okay with .023 tubes and .052 restrictions before. I think it might have came from the factory that way ??? how might this affect the way it runs? :o

What It's going on:
1987 350 TBI block bored .060 over
72cc Swirl Port TBI Heads
Cast Iron GM Manifold (modified to fit tbi heads)
Elgin MTC-1 Cam
flat top pistons w 4 valve releifs
(machinist said should be about 9.25:1 static compression)
Factory style HEI ignition
4-speed
Building this for low end torque, truck motor.

Cliff Ruggles:
Check the idle tubes again, they should be closer to .032" not .023".

That carb has a slightly larger lower IAB and will be fine with .052" DCR's for an engine making high vacuum at idle speed.

What are the specs on that cam, same as the Melling version, 204/214/112?.....Cliff

Greasy Harley:
Thanks for your response, Cliff

The idle tubes were super small, a #71drill bit fit with a tiny bit of play, #72 did not fit.(about .023)
The bleed tubes in the air horn are also .023. Neither look[ed] damaged or tampered with.
It's cool, I have lots of drill bits.  8)

Cam specs are:
Hydraulic Flat Tappet, Advertised Duration, 278/288, .420 in./.433 in Lift

Intake Valve Lift with Factory Rocker Arm Ratio: 0.420 in.

Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.433 in.

Valve Lift with Factory Rocker Arm Ratio: 0.420 int./0.433 ex

Thanks again  -Russ

77cruiser:
What's the lobe separation & duration @ .050?

Greasy Harley:
Intake Duration at 050 inch Lift: 204

Exhaust Duration at 050 inch Lift: 214

Duration at 050 inch Lift: 204 int./214 exh.

Advertised Intake Duration: 278

Advertised Exhaust Duration: 288

Advertised Duration: 278 int./288 exh.

Intake Valve Lift with Factory Rocker Arm Ratio: 0.420 in.

Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.433 in.

Valve Lift with Factory Rocker Arm Ratio: 0.420 int./0.438 exh.

Lobe Separation (degrees): 112

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