Idle Channel Restrictions

[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?

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. 

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

[tayto]

Did you CC the heads? As far as I know all TBI heads are 64cc. I am building a similar motor to yours with TBI heads 191 casting (same as 193 casting).

[Cliff Ruggles]

What size are the upper and lower idle air bleeds?.....

[Greasy Harley]

Ok lets see if i can get this right.
Idle tubes .036
Idle restrictions .052

Upper air bleeds in the air horn, as per Page 119 (bottom left pic) .0845

There is also an upper air bleed in the main body, as per page 119 (bottom right pic) Those holes are.695

It has both sets of holes.   ...should it only have one set?

Lower air bleeds as per page 96 (bottom left pic) are .075

I'm a little lost and having a bit of trouble with some of the terminology, so I hope I'm answering the question.

-Russ

[429bbf]

the terminology can be a little confusing  the first size you gave would be the main air bleed the second and third sizes you gave would be the upper and lower idle air bleeds . hths

[Greasy Harley]

the terminology can be a little confusing  the first size you gave would be the main air bleed the second and third sizes you gave would be the upper and lower idle air bleeds . hths

Okay, thanks for clearing that up. there is quite a bit of information 
I do feel like I am learning quite a bit.
So what I have is:

upper Idle air bleeds   -------    .695
lower idle air bleeds    -------    .075
idle tubes     ----------------    .036
idle restrictions    -----------    .052
main air bleed (air horn)    --    .0845
idle screw holes     ----------    .0575
acc. pump discharge holes   -   .028
fuel inlet seat (no window)    -  .125
primary jets      ------------      74
primary Rods     -----------       50c
Float level  ? Book says 1/4, GM says 15/32, many people say "set it lower for off road" (I go off road sometimes) I'm  thinking 3/8?

I appreciate the help.
-Russ

[Cliff Ruggles]

Set the float at 9/16".

Open up the holes under the mixture screw holes to .089".

The rest will be fine with that engine/cam combo.

I'd use a larger fuel inlet seat.....Cliff

[Greasy Harley]

Set the float at 9/16".

Open up the holes under the mixture screw holes to .089".

The rest will be fine with that engine/cam combo.

I'd use a larger fuel inlet seat.....Cliff

10-4!
Thank you!

[tayto]

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.

I just got my set of 191 TBI heads cc'd last week and they were 65 cc. 193 castings will be the same FYI. You may want to check your static compression again unless you've worked the combustion chamber then ignore me.