New Qjet carb - Starts, then dies

[RustyPile]

Originally Posted by dz1087

How do you loosen this thing up? Mine keeps going back in to high idle after I drop it down in to the lower idle setting while beginning my drive. Very annoying to have the thing keep dropping back in to high idle while driving for the first 10 minutes or so. Only does it when its 60 or less outside.

I don't know your level of knowledge about automatic chokes, so I'll start with the very basics of how it works. The choke mechanism is located on the passenger side of the carburetor. There is a round black plastic housing that covers the bi-metal spring that controls the choke blade located at the top of the carburetor. This cover is held in place by 3 small screws located around the perimeter of that cover. The spring is temperature sensitive. When cold, it winds up (tightens) and pulls the choke blade closed. When heat is applied (either by electric current or from heated air) it unwinds (loosens) and the choke opens up gradually.

The spring tension is adjustable. In your case, the spring needs to have a looser setting.. The setting is done with absolutely no heat in the engine. With the engine stone cold, having sat overnight, loosen those 3 retaining screws. It's not necessary to remove them, just loosen them a turn or two. Prop the throttle open to release tension on the fast idle mechanism. Rotate the black cover in the direction that causes the choke blade to open. Rotate it until the choke is fully open. Rotate the cover back the other direction until the choke fully closes. Rotate the cover another 1/8". Hold it in position and tighten the screws. If all other adjustments are correct, the choke should be fully open after about 3 - 5 minutes of run time, depending on outside air temperature. If the choke opens too fast, turn the cover another 1/8". After initial adjustment of the spring, any additional adjustments should be very small amounts.

For fast idle speed adjustments, refer to my previous posts on this thread for those settings.

[geezer#99]

Good post Rusty, but he has a divorced choke.
Could you explain how to set one up for leaner or richer settings.

[RustyPile]

Originally Posted by geezer#99

Good post Rusty, but he has a divorced choke.
Could you explain how to set one up for leaner or richer settings.

I don't see where he actually stated which choke he has. Maybe he'll come back and enlighten me.. If he does indeed have a divorced choke, there's not much adjustment range, or accommodating broad climate (temperature) changes.

First, the heat riser passage in the intake manifold and heads must be clean and clear. The heat riser valve must be fully operational. With mileage accumulation, this passage often becomes clogged with carbon buildup. This inhibits the transfer of heat into the choke stove. Here's the adjustment procedure.

Move choke rod in coil to end of its travel. Top of the choke rod should be even with the bottom of the hole it goes in. Bend rod in middle to adjust to top of rod even with bottom of hole, rod should be against the travel stop. This does not adjust the tension that controls opening speed, it adjusts closing tension.
If done properly and the choke still opens too slowly, the bi-metal spring is going bad. Replace it.

[Davidf]

I couldn’t get my divorce chock to release quickly enough, so I got rid of it with an LS swap…no more choke issue. Worth it!

[geezer#99]

He has another thread about the high idle on his carb.
I found this. Has a diagram of what you described.

To cure his problem likely he just needs to make his rod slightly longer.
Lots of times the coil isn’t worn out. A new one might do the same. The crossover passage can get plugged too.

I always had two rods available. One for summer, one for winter. Made from old wire coat hangers.




https://forums.aaca.org/topic/355944...966-chevy-396/

[Steeveedee]

Originally Posted by geezer#99

He has another thread about the high idle on his carb.
I found this. Has a diagram of what you described.

To cure his problem likely he just needs to make his rod slightly longer.
Lots of times the coil isn’t worn out. A new one might do the same. The crossover passage can get plugged too.

I always had two rods available. One for summer, one for winter. Made from old wire coat hangers.




https://forums.aaca.org/topic/355944...966-chevy-396/

Glad to see I'm not the only po boy on this site! I'm not so po now, but I've done this very thing when I was...and caught heck for cutting up a wire coat hanger.

[geezer#99]

Originally Posted by Steeveedee

Glad to see I'm not the only po boy on this site! I'm not so po now, but I've done this very thing when I was...and caught heck for cutting up a wire coat hanger.

LOL!
I had to sneak them outta the house!

Stashed them with the turkey baster that I ‘borrowed’ too!

[Rich72C10]

I replaced my Divorced Choke with an electronic one. It is still a Divorced Choke and sits in the same place on the intake. Then it has a little sensor mounted on the intake and the power is spliced from the anti dieseling solenoid's power.

Bending choke rod = no fun. I could hardly figure out how to adjusted it correctly with simply twisting it left/right Ha!

[1968_K20_4x4]

Originally Posted by RustyPile

"Slightly open" is not a proper adjustment. If you live in a cold climate, The cold engine choke and fast idle settings need to be "tighter" than what's needed in warmer climates.

Adjust the choke pull to open the choke about 1/8" to 3/16".. Do this with the engine cold, not running. Choke closed and using a hand-held vacuum pump, pull the choke open. Bend the linkage to achieve this setting.. Screw in the fast idle adjustment screw a few turns. Bump the throttle to set the fast idle screw on the top "notch" of the fast idle cam. Start the engine and immediately set the fast idle RPM around 1200 - 1300 Rpm.

During my days as a driveability tech, during initial start-up, I've had to set the fast idle at 1800-1900 RPM to keep an exceedingly "cold natured" engine running in the dead of winter.. After running at that speed for 15 - 20 seconds, a light tap on the throttle will bring the fast idle cam down a notch or 2 and the still cold engine will run about 850-1000 RPM and do just fine. Such drastic and aggressive settings aren't required in our most southern states.

All this assumes you have already set the proper ignition timing.

Many thanks to RustyPile!! You're a genius!

I finally got a chance to get out in the garage and start working on the truck again today. I did exactly as instructed, and my truck fired right up and ran beautifully! Never stalled or hesitated at all. Thank you so much for this info, you helped me get my truck up and running great again. One other thing that I checked was the torque on the carb mounting bolts and they were all a little bit loose.

Note to Richard- no worries at all I am glad that this thread also helped you get your truck running great as well.

Thanks to those who suggested a different choke setting for summer vs. winter, I will definitely keep that in mind and I may have to re-adjust come summer time. But I am very happy to know how to do that now!

Thanks again to everyone who replied to help me get this issue sorted out!

[1968_K20_4x4]

So in the summer, I will re-adjust my choke as needed.

When driving my truck around in the summer, will I also have to re-adjust the choke pull off? as in re-bend the linkage for summer operation? Or will the current setting be Ok for summer driving as well?

Thanks

[Rich72C10]

Originally Posted by 1968_K20_4x4

.... One other thing that I checked was the torque on the carb mounting bolts and they were all a little bit loose. ....

Word to the wise, don't torque and 100% don't over torque - the fellow that rebuilt my carb (Cliff Ruggles of Cliffs High Performance) said this:

Originally Posted by Cliff Ruggles

Don’t torque the bolts just snug them down, torquing them will warp the carb and can cause the secondaries to stick open slightly.

I then pointed out the GM manual about torque and he followed up again

Originally Posted by Cliff Ruggles

NO, do not torque those bolts or you will ruin the carburetor.......

So, ya I don't torque as I don't want Cliff to pop one on up side my head. LOL

[RustyPile]

Originally Posted by 1968_K20_4x4

So in the summer, I will re-adjust my choke as needed.

When driving my truck around in the summer, will I also have to re-adjust the choke pull off? as in re-bend the linkage for summer operation? Or will the current setting be Ok for summer driving as well?

Thanks

Thanks for the praise, but I assure you I'm no genius. Just well trained by GM's Houston, Tx training center and backed by YEARS of experience back in the day. As I've stated in other posts, I once did this on a daily basis for a living.

Now to answer your question on the choke pull. Once you have it adjusted you shouldn't have to adjust it for warmer weather. Some engines are more "cold natured" than others and may require a different setting on the choke spring for extremely cold temperatures vs. hot weather. The choke pull setting should work year 'round for you. I'd suggest you wait until summer (or warmer weather) shows up and see how the choke works for you. If the engine seems to run on the fast idle cam to long, mark the position of the choke housing and loosen those 3 screws. "Unwind" the choke spring. Do this in very small increments, about 1/8" at a time. I'm guessing you won't have to do any summer - winter changing.

[geezer#99]

Originally Posted by 1968_K20_4x4

So in the summer, I will re-adjust my choke as needed.

When driving my truck around in the summer, will I also have to re-adjust the choke pull off? as in re-bend the linkage for summer operation? Or will the current setting be Ok for summer driving as well?

Thanks

You’ll need to wait and see if you need to adjust again.
Problem is your season changes aren’t always consistent. The transition times from summer to fall and then winter and spring to summer will vary.
You just need to wait and see how your motor reacts.
I’ve found I needed a lot of patience to wait as long as possible before I changed
Settings.
I spent the first 55 years living in 40 below country. Mostly in Alberta where I’ve seen temperature swings of 40 below to zero and back to 40 below in but 6 hours.
My ultimate cure was using a manual choke on any carb. Always worked the same way year round.

[1968_K20_4x4]

Originally Posted by Rich72C10

Word to the wise, don't torque and 100% don't over torque - the fellow that rebuilt my carb (Cliff Ruggles of Cliffs High Performance) said this:


I then pointed out the GM manual about torque and he followed up again


So, ya I don't torque as I don't want Cliff to pop one on up side my head. LOL

Thanks for the heads up on this- to clarify I didn't actually torque the bolts down like the manual says as I don't have a torque wrench that goes down that low. I just snugged them up with my ratchet- I tightened them up but hopefully I didn't go too tight!

[1968_K20_4x4]

Thanks guys for the advice about adjusting the choke. I will see how the truck runs in the summer and reference this thread again if I do need to make some adjustments. Most of the driving I will do will be in the summer, but I want the truck to start reliably and consistently in cold weather as well for the few occasions where I do want to use it on freezing cold days the fall.

Thanks again for all the help and knowledge! I couldn't keep these old trucks running without all your help!

[dz1087]

Originally Posted by RustyPile

I don't see where he actually stated which choke he has. Maybe he'll come back and enlighten me.. If he does indeed have a divorced choke, there's not much adjustment range, or accommodating broad climate (temperature) changes.

First, the heat riser passage in the intake manifold and heads must be clean and clear. The heat riser valve must be fully operational. With mileage accumulation, this passage often becomes clogged with carbon buildup. This inhibits the transfer of heat into the choke stove. Here's the adjustment procedure.

Move choke rod in coil to end of its travel. Top of the choke rod should be even with the bottom of the hole it goes in. Bend rod in middle to adjust to top of rod even with bottom of hole, rod should be against the travel stop. This does not adjust the tension that controls opening speed, it adjusts closing tension.
If done properly and the choke still opens too slowly, the bi-metal spring is going bad. Replace it.

Yeah, I've got the divorced choke. Thanks for the writeup. I'm thinking my bimetal is going bad since it takes forever to open up.

Would it be wise to go ahead with an electric choke retrofit on this carb if I'm switching over to an aluminum intake manifold with no divorced choke provision?

[geezer#99]

Likely the bimetallic coil is fine.
Could be your intake crossover is plugged or partly plugged.
Or your heat riser is stuck or has been removed.
Electric choke kit is universal. You can use on any intake. Might just need a different mount for it.

[dz1087]

Originally Posted by geezer#99

Likely the bimetallic coil is fine.
Could be your intake crossover is plugged or partly plugged.
Or your heat riser is stuck or has been removed.
Electric choke kit is universal. You can use on any intake. Might just need a different mount for it.

Heat Riser = the pipe from the manifold to the flap on the breather assy? If so, then no, I don't have one.

Cross over should be nice and clean as the manifold was cleaned and checked by the machine shop when the engine was rebuilt 8,000 miles ago.

The choke system works great @ >60*F. It's when it's colder than that on start that it keeps trying to jump back in to high idle for about five minutes as I'm driving down the road. Just annoying.

[LockDoc]

Originally Posted by dz1087

Heat Riser = the pipe from the manifold to the flap on the breather assy? If so, then no, I don't have one.

Cross over should be nice and clean as the manifold was cleaned and checked by the machine shop when the engine was rebuilt 8,000 miles ago.

The choke system works great @ >60*F. It's when it's colder than that on start that it keeps trying to jump back in to high idle for about five minutes as I'm driving down the road. Just annoying.

Heat riser is at the bottom of the exhaust manifold. Between the manifold and the exhaust pipe.

https://www.jegs.com/i/OER+Equipment...r%20Categories

LockDoc
-

[dz1087]

Originally Posted by LockDoc

Heat riser is at the bottom of the exhaust manifold. Between the manifold and the exhaust pipe.

https://www.jegs.com/i/OER+Equipment...r%20Categories

LockDoc
-

Yeah, don’t have any of that assembly except the flap mechanism in the breather, but it’s stuck open.