APT adjustment question

[Greasy Harley]

I found instructions on how to set the APT using Vernier calipers. I followed that procedure and ended up with a lean condition. ( I don't think I did it wrong ?)
Using these instructions APT was set a fuzz over 2 turns up.
I pulled the top off the carb, removed the plug, verified that the rods were hanging evenly and reassembled.

I tried the tip-in procedure and the rpm's increased until the APT was 5 turns up ...but the exhaust was really stinky.
Was I doing the tip-in wrong?
* rpms up around 2k shut the choke flap 3/4 of the way, if the rpm's increase, raise the apt up 1/4 turn and repeat. do this 'til the rpms don't increase.*  Right?

I decided to shoot right down the middle, if 2 turns is too lean and 5 turns is too fat...
I adjusted it to 3.5 turns up and took it for a rip. It seems happy now. so that's cool, but I would really like to know where I went wrong with the tip-in.

Closing the flap too much? rpm's not high enough? Maybe I just suck?
Anybody point me to a GOOD video on tip-in procedure?

For what it's worth, the truck is a 79 k10 4x4, with a Granny 4 speed.

1 piece rear main 350 .060 over
Flat top slugs with 4 valve reliefs
9.8:1 compression
.040 quench
TBI heads
Lunati Voodoo 10120702:
Gross Valve Lift (Int/Exh): .468/.489
Duration @ .050 (Int/Exh): 219/227
Advertised Duration (Int/Exh): 262/268
Lobe Separation: 112
RPM Range: 1400-5800

I ain't trying to win any drag races , just trying to merge with 80mph commuter traffic.
Thanks to everybody here for loading this forum with quality information.
-Russ

[Greasy Harley]

so... actually, 3.5 turns is still a little fat judging by the puff of black smoke, but it does run pretty sweet. I'll turn the apt down 1/4 turn tomorrow and run it again.
This means my measuring procedure was closer than my tip-in procedure. Sure would like to know what I'm doing wrong.

[Kenth]

I have found the APT screw does not touch the power piston pin until 2 turns up from seated.
Also, most of the carbs with this feature i have seen is set 3.5 - 4.0 turns up from factory.

I would like to see 50-100 rpms increase with slowly closed choke valve at 2200 rpms, this indicates a slightly leaned out mixture and works well.

I use the tip-in procedure after the idle/lowspeed circuit is sorted out.

[Cliff Ruggles]

Not enough information.

What is the carburetor part number?

What have you done to it and exactly how did you set it up, jets, rods, idle system, etc?

The APT is simply there to allow fine tuning the height of the PP and exactly where the tapered portion of the metering rods are in the jets at light engine load (high vacuum).

Also what are "TBI" heads, and what intake manifold?....

[Greasy Harley]

...most of the carbs with this feature i have seen is set 3.5 - 4.0 turns up from factory.

I would like to see 50-100 rpms increase with slowly closed choke valve at 2200 rpms, this indicates a slightly leaned out mixture and works well.

I use the tip-in procedure after the idle/lowspeed circuit is sorted out.

Factory settings are out the window since I straightened the hanger. idle circuit is tuned pretty good. sounds like I might not be preforming the tip-in procedure properly

Not enough information.

What is the carburetor part number?

What have you done to it and exactly how did you set it up, jets, rods, idle system, etc?

The APT is simply there to allow fine tuning the height of the PP and exactly where the tapered portion of the metering rods are in the jets at light engine load (high vacuum).

Also what are "TBI" heads, and what intake manifold?....

I don't have the carb number handy, but I could get it after work .It's a later model carb, I believe the factory carb for that '79 truck.
Mods:
Converted to electric choke
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 set to 9/16
your kit.
I also made some small notches in the secondary air flaps
"TBI heads" swirl port heads that came factory on an '88 Suburban with a 350. mated to a cast iron Q-Jet manifold with modified center bolt holes.

Only problem I'm having now is after driving through a neighborhood (slightly above idle), there is a puff of smoke when I stab the throttle taking off from the stop sign. It clears up after that and is new since I adjusted the apt. I think this means the PP is still a little too high?

[Kenth]

50C rods are for the earlier 4MV/MC style Qjet.
Most later M4MC Truck Qjets uses rods with M suffix.
.0575" idle needle holes are somewhat small for non-emission usage, i would enlarge to at least .085".
Float at 9/16" is rather low, i would aim for at least 13/32".

FWIW

[Cliff Ruggles]

He's probably using my 50C rods, custom from .050" to .036" full taper.

Idle system is a little on the lean side for what you are doing.  Do you have full control from rich to lean with the idle mixture screws?

The swirl port heads are excellent for a truck or towing build, not so much for "high performance" work.

I think I have a 1987 Monte Carlo SS intake around here someplace that fits those heads......

[Greasy Harley]

50C rods are for the earlier 4MV/MC style Qjet.
Most later M4MC Truck Qjets uses rods with M suffix.
.0575" idle needle holes are somewhat small for non-emission usage, i would enlarge to at least .085".
Float at 9/16" is rather low, i would aim for at least 13/32".

FWIW

*EDIT**
Idle needle holes are actually .089
And I was having trouble with low float and raised the float just a touch. no problems since.
Sorry, it's been a while and I was looking up specs from my old posts.

He's probably using my 50C rods, custom from .050" to .036" full taper.

Idle system is a little on the lean side for what you are doing.  Do you have full control from rich to lean with the idle mixture screws?

The swirl port heads are excellent for a truck or towing build, not so much for "high performance" work.

I think I have a 1987 Monte Carlo SS intake around here someplace that fits those heads......

Yes, they are your rods, jets etc.
Yes, I have full control of the idle circuit.

[Greasy Harley]

I think I got it. I turned the APT down 1/4 turn at a time 'til I got light detonation with the Vacuum adv, then I turned it up just over 1/4 turn. pulls hard, no detonation, no stumble.
I am still unclear what I was doing wrong during the tip-in procedure.
I am doing something wrong. The adjust and test method works, but it takes a lot more time.
Anybody have a link to a good tip-in procedure video?

[Cliff Ruggles]

We tune for results when driving, so nothing really to worry about.  The "tip-in" procedure helps get you close and insures you don't have the rods too far out of the jets (rich).  You should see or hear a very slight engine speed increase if the engine is running around 1800-2000rpm's on the fast idle when you gently close the choke flap just a tad......

[tayto]

I think I got it. I turned the APT down 1/4 turn at a time 'til I got light detonation with the Vacuum adv, then I turned it up just over 1/4 turn. pulls hard, no detonation, no stumble.
I am still unclear what I was doing wrong during the tip-in procedure.
I am doing something wrong. The adjust and test method works, but it takes a lot more time.
Anybody have a link to a good tip-in procedure video?

i have a similar engine build to yours.what octane did you end up running? how much mechanical and vac advance does your engine like?

[Greasy Harley]

i have a similar engine build to yours.what octane did you end up running? how much mechanical and vac advance does your engine like?

I run 91 octane 10% ethanol
Timing is set at 13° initial-33°all in
Sometimes i get a bad batch of gas and get a little pinging with the Vac-adv plugged in, so I just leave it unplugged. Makes my life easier.

[Glutenfreecarbs]

I ran TBI/swirl-port heads with a Q-jet for a few years, and my final recipe was 8° initial, 15° vacuum advance, and 16° mechanical advance, for 24° total at WOT. I used Mr. Gasket's "medium" distributor springs, and an Accel adjustable vac advance cannister, modified with an external spring to make it start pulling timing at around 10 inHg manifold vacuum.

Don't listen to the old-timers that say "every SBC wants 35° total timing." I've got two burnt head gaskets hanging on my wall that suggest otherwise...

[tayto]

TBI heads like 25-30* total timing.My engine made the most power with 26* total. had to convince the dyno operator to go down from 32* instead of up i can post dyno sheets later.