throtle response

[1tuffcj]

set the timing at 15 to 16 degrees btdc, idle at 900 rpm, when i go to launch it it stumbles then kicks in, you kinda have to feather it. and when i'm going down the road and step on it it goes then i noticed another stumble as i'm excellarating, need help. thanks mikey

[AMX69PHATTY]

Sounds like carb's accelerator pump adjustment.
Usually the culprit for an off idle stumble.
On a Holley there's the arm adjustment screw,a Cam, and a shooter.
What carb ?

[1tuffcj]

#-o sorry about that, i have a holly truck avenger 670. i been trying to get this thing running good all day, on and off. just did another test drive, it seemsw to run good once you get going. drove it for about 1 mile stoped at a freinds, went to start it and now the idle was all over the place, like it was gonna die unless i gave it gas. so i would peddle the gas and it would hessatate, then all of a sudden it would hook up and launch. i set the timming at 20 degrees btdc idle at 900 rpm, there was no pinging. but i get home to look it over and now the timming is at 22 degrees and idle is at 500 to 600. i also baught a vacuum gauge and hooked it up to port on the carb where the vacuum advance hose goes, and it only read 4 to 5 inches. help please, thanks mikey

[AMX69PHATTY]

A lot going on here.
Distrib Vac Advance should go to a Ported Vacuum connection,
that is no Vac at idle, but manifold vac off of idle.
This port is usually on the pass side of the front metering block.
If it has vac there at idle, the front flies are too far open.

Can't set the Accel Pump screw until idle speed is set.
Whith motor off, using idle speed screw, close front flies all the way.
then turn idle speed screw in 1-1/2 full turns opened from fully closed.

Now adjust Accel Pump screw, lengthen screw until there is NO PLAY in the pump arm at the idle position,
now open carb all the way and check that pump arm can still travel a little, ~.015.
This ensures the most accel shot without binding the pump.
I actually set them at WOT first, then check idle for no slop.

Did you check your float levels using the sight screws ?

Checking timing advance at idle with Vac Advance disconnected ?

[1tuffcj]

thanks for the help. in the holley manual, it said to hook up the timed spark vacuum source to that fitting witch they call (full manifold vacuum port). #2 when you say flies, there's 4 of them and 2 of them are for the secondary. so to close these turn thre curb idle speed screw, then turn back 1 1/2 turns #3 the pump screw is that the one with the spring around it, and the other end of that linkage hooks up to the throtle cable. so what i want is, when i move the throtle linkage i want the other end that goes to the fuel bowl to mve at the same time.#4 i don't see any screws at the fuel sight window, it's not even a window, it's solid.#5 how do i check the timming advance at idle with the vacuum advance disconected? do you mean with a vacuum gauge, put the gauge where the vacuum advance line goes to the carb at idle, and read the inches. thanks mikey. i was talking to fuzzy but he's at the drags, and with the time difference and work scheldaul, hard to hook up. he's helped me out alot with this 401. thanks for everyones help, got get it running good enough to melt the 35's for fuzzy :lo1l: 401 power.

[AMX69PHATTY]

#1 hook up the timed spark vacuum source to that fitting witch they call (full manifold vacuum port).

I've always attached Vacuum Advance to a PORTED Vacuum Port, no vac at idle.
On older Holleys, it's on the passenger side, near the front, but up on the side of the front metering block.
Now does this motor still have Full Emisions equipment on it ?
If so, that's a whole nother ball of wax, and I'm not aware of all the correct info.

#5 how do i check the timming advance at idle with the vacuum advance disconected?
do you mean with a vacuum gauge, put the gauge where the vacuum advance line goes to the carb at idle, and read the inches.

Just disconnect the Vac Advance hose from the Distributor and plug the hose with a golf tee.
Then set the initial timing, Vac Adv hose disconnected, and no vacuum gauge needed.

When checking engine vacuum, the gauge should be attached to the Intake Manifold.
My fitting for the Power Brake Booster has a 2nd nipple on it for a 1/8" vacuum hose


#2 when you say flies, there's 4 of them and 2 of them are for the secondary.
so to close these turn thre curb idle speed screw, then turn back 1 1/2 turns

Yes "flies" are carb Butterflies, 2 primary & 2 secondary.
Yes, close the fronts all the way with the curb idle screw, then re-open them about 1-1/2 turns.
This is a baseline setting, after starting it up, it should need closed down a little from there.
After starting, if they need opened much more than that to idle at the proper idle speed, it can cause other problems.
Curb Idle screw, counterclockwise = out = closing flies.

#3 the pump screw is that the one with the spring around it, and the other end of that linkage hooks up to the throtle cable.
so what i want is, when i move the throtle linkage i want the other end that goes to the fuel bowl to mve at the same time.

Yes. The throttle end of the Accelerator Pump Arm rides on a plastic cam attached to the bottom backside of the throttle cable plate. The screw with the spring around it is on the other end at the front and actuates an arm on the bottom of the fuel bowl.
There should be NO SLOP between the Arm and the Cam at the Idel speed position.
Basically make the screw with the spring and lock nut as long as possible,
But then check, with motor off, and the carb taken to wide open throttle, that the smaller accel pump arm on the bottom of the fuel bowl will still move a little bit farther down, like .015", than the screw & spring are pushing it. This prevent binding the Accel Pump. Getting this right should solve all off idle hesitations. This should be done after idle speed is set.

#4 i don't see any screws at the fuel sight window, it's not even a window, it's solid.

The fuel bowl sight level screws are usally solid brass. After other sdjustments are made and it will idle decent, with it idleing,
remove the flat brass float sight level screws form the passenger side of the fuel bowls one at a time. When it is idleing fule should come up just to the bottom of the holes and barely weep out. If you shake the vehichle, it should slosh out.

[1tuffcj]

my power brake's hook to the carb, it says right in the manuale. holley truck avenger 670, so where should i test for vacuum? at that spot on the carb or in the front where the full manifold vacuum port is (where my vacuum advance line goes). thanks mikey. sorry for the confusion, i'm useing the edlebrock airgap intake