86k5 Quad-jet issue

[Justin Fleming]

Can anyone offer up any ideas...

It appears that the electric choke mechanisim is not release causing the truck to run bad after it is at operating temp. I notice that the throtle linkage is never making it back to the home position/idle position. So after digging around I relized something in the chock mech. is holding it up. When I manually release it everything comes home and works well. The question is what is replacable that will fix the issue? Is there an element behind the round black cover?


thanks

 

[dyeager535]

The whole black cover needs replacing if it's bad. All one piece.

You might try spraying carb cleaner back there, see if that frees it up.

Does the choke open at all after its been running for a few minutes, or does it appear to be "frozen" in one spot?

 

[Justin Fleming]

No it opens...It just appears to never open all the way unless I assit in manually releasing it. This issue just started showing up recently and in the past it has functioned properly. I am wondering if the abnomal temps and the fact that I is not a daily driver (Plow Truck) that it just might be sticking....

 

[dyeager535]

Gah, I hate chokes. I was going to say that it could be linkage and say again to clean it, but I can't remember if binding linkage will stop the choke from opening all the way. It probably will. There is only one piece that opens the choke though, it's the rod attached to the choke blade, everything else hinges on that moving thorugh it's whole range of motion.

With no other changes, the "throw" shouldn't decrease or increase...the electric chokes are on a timer, so they don't even care how hot the engine gets. I don't know if they even use a coil in them, not sure I've personally ever taken one apart.

 

[Justin Fleming]

Something so simple always ends up being so complicated. What happend to the old pull out choke lever that you pushed in when you felt the truck was ready to be off choke.....lol


thanks for the ideas

 

[Mike D]

With the engine off, but warm, manually open the throttle ( or have a buddy hold the gas pedle to the floor ). Take a flashlight and shine it at the front choke side of the linkage. There is a little screw that can be adjusted that helps set the fast idle. If you turn that screw counterclockwise 1/4 turn it may allow the choke weight ( the thing you touch to release the choke ) to unload. When the choke is on, the rear two barrels of the Q-jet are locked out. That whole area gets mighty grimy with time.

 

[apache]

Dont forget about the choke pull off which is the vaccume operated chingadera behind the heat/choke element. My 84`s is a pig when the choke is on which seems to be way to long with way to high of a high idle although the element works. Mine is not adjustable because the cover is notched and only fits in the casting one way,yours might be adjustable. Also if you pull it off to inspect it make sure the tang on the element is engaging the choke tab and not on the wrong side of it.

 

[Justin Fleming]

With the engine off, but warm, manually open the throttle ( or have a buddy hold the gas pedle to the floor ). Take a flashlight and shine it at the front choke side of the linkage. There is a little screw that can be adjusted that helps set the fast idle. If you turn that screw counterclockwise 1/4 turn it may allow the choke weight ( the thing you touch to release the choke ) to unload. When the choke is on, the rear two barrels of the Q-jet are locked out. That whole area gets mighty grimy with time.

How does backing down the fast idle screw allow the choke weight to release?

I need to tear into it and see what I can find, It has been 3 years or so sense I rebuilt the carb.

 

[dyeager535]

Choke pull off is only there to crack the choke plate open once the engine starts.

Proper operation of the choke as viewed from the choke plate:

Kick the throttle on a cold engine, choke plate snaps completely shut.

Crank engine over, engine starts, starts pulling vacuum, which forces choke break to open the choke plate a minute amount so more air gets into the motor.

As the motor (or choke coil more correctly) heats up, the choke plate gradually opens until it is vertical. If you can't adjust the choke coil tension, but its not opening fully, then you need to straighten the choke rod out just a hair, if all else is working right.

 

[Justin Fleming]

So I got into it a little tonight and everything is releasing freely and working properly on the chocke. Once the vechicle is warmed up and you smack the gas once the choke release to the straight up and down position. My father told me today that he lubed the linkages up the other day. I cleaned everthing again and relubed it.

It seems as if you let the truck run at iddle for a few minutes then the truck starts to load up. So I almost think something is sticking or getting pluged internally to the carb. The fuel pump on the carb seems to be working well when you check for the fuel spray, the meetering vavles for the secondary seem to be moving freely, the timing is good and the vaccum advance on the timing is working well also.....

Refresh my memory on the quad-jet how many turns out is a good base point on the mixture screws and what direction does what? I would like to check this as it is possible someone might have messed with them but not likely.

thanks

Choke pull off is only there to crack the choke plate open once the engine starts.

Proper operation of the choke as viewed from the choke plate:

Kick the throttle on a cold engine, choke plate snaps completely shut.

Crank engine over, engine starts, starts pulling vacuum, which forces choke break to open the choke plate a minute amount so more air gets into the motor.

As the motor (or choke coil more correctly) heats up, the choke plate gradually opens until it is vertical. If you can't adjust the choke coil tension, but its not opening fully, then you need to straighten the choke rod out just a hair, if all else is working right.

 

[dyeager535]

All the way flush, two and a half turns out is usually a good starting point.

My dad was having a problem with poor idle on his just awhile back, for some reason the power piston was stuck, primary needles therefore weren't moving right.

I think I'd remove the lube on the linkage, it's a dust attractor and I don't think any of it NEEDS lube, but it would need to be free of dirt too. Just me.

 

[Justin Fleming]

All the way flush, two and a half turns out is usually a good starting point.

My dad was having a problem with poor idle on his just awhile back, for some reason the power piston was stuck, primary needles therefore weren't moving right.

I think I'd remove the lube on the linkage, it's a dust attractor and I don't think any of it NEEDS lube, but it would need to be free of dirt too. Just me.

I cleaned everything again, left it with out lube. I set the mixture screws 2 1/2 turns out, added some fuel system cleaner, tank of 94 and some water remover and things seem normal again.... If I decide the truck is to rich would I back the screws out or take them in. If I remember right out is lean and in is rich, which is differnt than what I am used to for tuning bikes.

 

[Blue85]

Backing the screws out adds fuel. Sometimes the "off-idle" circuit is working even when you are at idle, so after a point the idle mixture screws don't have any effect. I've also seen the tips of the mixture screws bent and/or broken so that mixture is different on the two sides of the carb.

 

[dyeager535]

Just to clarify, these screws only adjust *idle* mixture. Rich/lean at any other throttle position is done elsewhere.

 

[Justin Fleming]

Just to clarify, these screws only adjust *idle* mixture. Rich/lean at any other throttle position is done elsewhere.

My truck exhaust always seem to smell real rich all the time at idle....So Idealy I could go in on both screws a little at a time and then check driveability....

 

[dyeager535]

That is of course assuming it's rich. Apparently lean can smell like it's rich as well. That's just going off of what someone who has far more experience than I once said.

That is how I did it "back in the day" though, adjust the idle mix until it smells right. Of course, you are supposed to do it by going for the highest vacuum, and IIRC, that also includes messing with base timing.

 

[Blue85]

Apparently lean can smell like it's rich as well.

Smelling rich just means there is unburned fuel coming out. If the mixture is too lean, the engine starts to misfire. Again, you have some raw fuel coming out. An oxygen sensor has the same problem. Once you start to misfire, there is lots of O2 in the exhaust so the sensor says you are rich.