idle screws inop

[baxsom]

ok, i am totally ignorant to quadrajets but i learned to tune a holley pretty decently on my old mustang.
that being said.
i have been trying to chase down a very rich condition on my 72 454.
as in so rich it fouls plugs, stings the eyes and blows smoke out the pipes (black)

at idle, the mixture screws are all the way in and the engine still cranks and runs and idles all the way down to 500rpms in park with no problems.
i cant find a vacuum leak anywhere but i am fairly certain that this is not normal.

 

[gmjunkie]

ok, i am totally ignorant to quadrajets but i learned to tune a holley pretty decently on my old mustang.
that being said.
i have been trying to chase down a very rich condition on my 72 454.
as in so rich it fouls plugs, stings the eyes and blows smoke out the pipes (black)

at idle, the mixture screws are all the way in and the engine still cranks and runs and idles all the way down to 500rpms in park with no problems.
i cant find a vacuum leak anywhere but i am fairly certain that this is not normal.

I'd check the lead plugs in the bottom of the float bowl,there known to leak gas with some age!!Makes them run big time rich,and the idle air screws won't change a thing!!

 

[MMM]

Also check the float. Q-Jet floats are notorious for breaking down and absorbing gas. Lets fuel overflow the bowl.

Every time I rebuild a Q-Jet I replace the float automatically.

Mike

 

[Hib Halverson]

Like junk says, check the well plugs first.

Could be the sunk float thing but usually then that happens the motor won't even run at all and you'll see gas pouring out of the boosters.

Also, with an over-rich sitch, a vac. leak is the opposite extreme, that is, if you got black smoke out the exhaust, it's highly unlikely you have a vac. leak.

Again, check the well plugs. I betcha they're pissin' fuel into the motor and, since it leaks under the throttle plates, you never see it.

 

[baxsom]

would it help to diagnose if i said that it was a brand new carb that was advertised as the plugs epoxied over.

like i said though i am new to qjets so i am not even 100% sure i know where the plugs or floats are.

(i am getting very close to getting the torker II and a holley, at least those i can work on)

 

[JohnZ]

If it runs with the idle mixture screws turned in all the way and adjusting them has no effect, the throttle plate is too far open, and it's idling on the transfer slot. Back off the idle speed screw to close the throttle plate down, back the idle mixture screws out about 1-1/2 turns, start it, and adjust the idle mixture screws for highest steady vacuum with a vacuum gauge connected to full manifold vacuum.

 

[gmjunkie]

would it help to diagnose if i said that it was a brand new carb that was advertised as the plugs epoxied over.

Yeah,That would have helped!!But if it was a Brand New carb,it wouldn't need the plugs epoxied!!

If it runs with the idle mixture screws turned in all the way and adjusting them has no effect, the throttle plate is too far open, and it's idling on the transfer slot. Back off the idle speed screw to close the throttle plate down, back the idle mixture screws out about 1-1/2 turns, start it, and adjust the idle mixture screws for highest steady vacuum with a vacuum gauge connected to full manifold vacuum.

I agree with JohnZ in light of the new info!!

 

[baxsom]

If it runs with the idle mixture screws turned in all the way and adjusting them has no effect, the throttle plate is too far open, and it's idling on the transfer slot. Back off the idle speed screw to close the throttle plate down, back the idle mixture screws out about 1-1/2 turns, start it, and adjust the idle mixture screws for highest steady vacuum with a vacuum gauge connected to full manifold vacuum.

it is currently running at 500rpms with the idle screws all the way in.
you are saying that i need to back it off more until the engine dies and then go from there right?

 

[baxsom]

wow
looks like bubba got me too.

i decided to go ahead and replace the intake gaskets just to make sure there are no vacuum leaks.

i drain the coolant and unbolt the thermostat gasket housing.

lo and behold there is no thermostat installed.

why would someone do that.
it never overheated but it would take forever to get up to 200 degrees where it would stabilize.

anyway the rear gasket on the intake was ripped right at the head. i am thinking that was my vacuum leak.

 

[gmjunkie]

anyway the rear gasket on the intake was ripped right at the head. i am thinking that was my vacuum leak.

Are we talking about the gasket manifold to head or the narrow rubber gasket across the back of the block manifold to block??

 

[baxsom]

Are we talking about the gasket manifold to head or the narrow rubber gasket across the back of the block manifold to block??

we are talking the narrow gasket on the back of the block that goes left and right. most people use rtv to seal it.
the previous owner i guess used the rubber seals that came with the intake gasket kit.


at least i hope that was the problem.

 

[gmjunkie]

at least i hope that was the problem.

Well,I'm willing to bet it's not!! The worst scenario is,it would cause a Oil Leak down the back of the engine!!I believe I would go with JohnZ's recommendation's,he's probly forgot more about GM products than most of us on this forum (Or any other forum!!) will ever know!!!

 

[baxsom]

Well,I'm willing to bet it's not!! The worst scenario is,it would cause a Oil Leak down the back of the engine!!I believe I would go with JohnZ's recommendation's,he's probly forgot more about GM products than most of us on this forum (Or any other forum!!) will ever know!!!

i saw that but i just wanted to make sure just in case. intakes are easy enough to remove and install.

just to make sure, i get the car running again with the idle screws all the way in and then turn the idle screw out until the engine dies.

then turn the mixture screws 1.5 out and see if it starts. then adjust with vacuum gauge.

 

[Vettehead Mikey]

just to make sure, i get the car running again with the idle screws all the way in and then turn the idle screw out until the engine dies.

then turn the mixture screws 1.5 out and see if it starts. then adjust with vacuum gauge.

Doesn't sound right to me.

Set the MIXTURE screws to 1 1/2 turns open.
Start the engine.
Adjust the IDLE screw (there's only one) to get the correct speed.
With the vacuum gauge attached, adjust eh MIXTURE screws (there's two) to get max imum reading.
Readjust the IDLE screw as required to maintain the correct speed.

 

[Vette79]

As mentioned previously, start with them already turned out. Hook up the vacuum guage and turn each idle screw out till you reach max vacuum. Then turn back in a 1/4 of a turn for best lean condition. Afterward, you will have to adjust your idle.

 

[baxsom]

thats what i have been trying to say.
it runs with the mixture screws turned all the way in shutting the fuel complelty off of the idle circuit.
any turns out makes it run even richer.

it will idle all the way down until the idle screw is no longer touching the stops.

one person posted that the plates were set too far open so that the throttle plates were past the transfer slots.

the only way to make sure that they were not past the transfer slots was to close the plates as far as they would go. they wont close any farther and the car still runs.

no reason to make it even richer by opening the screws out 1.5 turns when it blacks the plugs turned all the way in.

 

[gmjunkie]

If it runs with the idle mixture screws turned in all the way and adjusting them has no effect, the throttle plate is too far open, and it's idling on the transfer slot. Back off the idle speed screw to close the throttle plate down, back the idle mixture screws out about 1-1/2 turns, start it, and adjust the idle mixture screws for highest steady vacuum with a vacuum gauge connected to full manifold vacuum.

it is currently running at 500rpms with the idle screws all the way in.
you are saying that i need to back it off more until the engine dies and then go from there right?

I think what JohnZ is saying is,you need to back off the Idle Speed screw so that the throttle plats are completely closed!! Then set idle mixture screws out about 1-1 1/2 turns! Start engine and adjust idle mixture screws till you get the highest "Steady" vacuum with a vacuum gauge connected to full manifold vacuum.(Manifold Vacuum) not from a port on the carb!! After that you can set your Idle speed!!

PS. JohnZ correct me if I'm wrong!!

 

[gmjunkie]

thats what i have been trying to say.
it runs with the mixture screws turned all the way in shutting the fuel complelty off of the idle circuit.
any turns out makes it run even richer.

it will idle all the way down until the idle screw is no longer touching the stops.

one person posted that the plates were set too far open so that the throttle plates were past the transfer slots.

the only way to make sure that they were not past the transfer slots was to close the plates as far as they would go. they wont close any farther and the car still runs.

no reason to make it even richer by opening the screws out 1.5 turns when it blacks the plugs turned all the way in.

If that be the case,then either the well plugs are leaking,the float is set too high,or the float is gas logged!!

 

[magoo]

Just a dumb thought. Don't some Q-jets have a throttle plate adjustment screw in the secondary like some of the Holleys?

Mike

 

[JohnZ]

Make sure your throttle cable/linkage isn't holding the throttle plate from closing any further; when you back off the idle speed screw so there's a gap between the end of the screw and the throttle lever on the shaft, the plates should be fully closed. This assumes your choke linkage isn't stuck and holding the shaft on the fast idle cam.