Q-jet carb adjustment 101

[jimboh247]

First question: Can you unplug vacuum lines that are in the way of the idle adjustment screws in order to adjust the screws? I assume you have to plug them so you don't have massive vacuum leaks.

Second question: Is it ok to adjust up the idle with the screw to move the throttle position up/down in order to keep it running while adjusting the idle screws?

[C-10 simplex]

1) Not sure----would need a picture to say for sure.....and even then.....


2) Probably not; i think this is the whole purpose of adjusting idle mixture----if you were to rev it up this would change the vacuum output of the engine.

There may be other issues if you can't get it to idle normally.

[jimboh247]

Thanks for the reply.

This is my 1st attempt to adjust a carb.

Let me describe what I have. Cold startup: It won't start unless I pour a little gas down the throat. That's a choke adjustment, correct? Which way should I turn it when I adjust it?

Once the truck starts, the idle is choppy and will shut off if you do not give it gas. Again a choke adjustment, correct?

Once the truck is warm, it runs well if you are accellerating, but once you let off the gas, the idle drops low. Sometimes it will stall, but always restarts without trouble. Idle mixture screw adjustment, correct?

Does anyone make a tool that makes idle mixture screw adjustments easier?

Also, where is the best place to hook up a vacuum guage? Will a port on the carb work? Does the port have to be below the throttle blades to get the best signal?

I found a few potential vacuum leaks that I fixed.

[motornut]

Originally Posted by jimboh247

Thanks for the reply.

This is my 1st attempt to adjust a carb.

Let me describe what I have. Cold startup: It won't start unless I pour a little gas down the throat. That's a choke adjustment, correct? Which way should I turn it when I adjust it?

Once the truck starts, the idle is choppy and will shut off if you do not give it gas. Again a choke adjustment, correct?

Once the truck is warm, it runs well if you are accellerating, but once you let off the gas, the idle drops low. Sometimes it will stall, but always restarts without trouble. Idle mixture screw adjustment, correct?

Does anyone make a tool that makes idle mixture screw adjustments easier?

Also, where is the best place to hook up a vacuum guage? Will a port on the carb work? Does the port have to be below the throttle blades to get the best signal?

I found a few potential vacuum leaks that I fixed.

may wana check for gas line leaks too
seen broken sending units act like that
yes they do make a tool for ajusting,ask most prob still sell them
the vac advance for the dizzy,is one that starts after the plates move
the gauge should be on one that dosn't

[C-10 simplex]

1) Not nessesarily---first off how are you starting up? Could be accelerator pump, maybe choke, maybe not. The carb may be leaking or could be a float problem.

How cold is it right now in Lexington? If you have to adjust the choke then as far as which way to turn, i think you have to let everything cool off, put the throttle on the highest step on the fast idle cam and turn the coil until the choke flap just closes. i think.

2) Could be. Could also be a float problem.

3) Could be, but also sounds like float. If the float is leaky than big problems as far as tuning.

4) Yeah, but you can do it with a small screwdriver.

5) i don't remember, will check asap

i wish i had more time to help but i'm kind of busy (translation= also i'm not real sure about any of this). i hope the better carbologists can chime in and help.

[CaliDude76]

Exactly what type of carb are you trying to adjust??? what year truck... there is a fast idle(cold choke) adjustment on the left hand side of the carb, if your standing in front of the truck.. you do need to have all vacuum lines connected to get the proper feedback from the carb....

Again, it depends on what carb you have.. I have a Q-Jet M4ME Series

Here's the tool you need that makes a huge differemce in adjusting the air mixture idle screws

[jimboh247]

Adjusted the idle mixture screws and was able to get 18 on the vacuum guage. Adjusted them out about 4 full turns. Any more or less, and the vacuum falls.

Idle is nice and smooth.

Thanks for the help!