[track73]

My 79 800 Qjet doesn't kick down to about 1500 rpm after I start the engine. It has a "Cliffs" kit with all the stuff he recommended for my build. The engine starts right away but idles too fast over 2000. The engine runs great after it warms up but it's a PITA trying to keep it running for what seems like an eternity, But is probably less that 8 minutes in the summer. I don't drive it much in the winter because of the problem, so I don't have an idea on how long it takes to get to OT. I have fiddled with the fast idle screw and looked at the linkage and nothing seems to be out of order. I wonder what I missed when putting the carb back together. BTW I put on an Eclin electric choke that I had laying around and it works fine . Maybe set it leaner or richer?

[steve25]

Do this check.
Get the motor up to normal operating temp then remove the Carb and with it sitting in a normal position and with the choke hold full openback out the idle speed screw all the way back to the bracket it passes thru.
Next flip the Carb over and you should see the primary throttle blades fully seated in there Bore.
If you do not then something is holding them open.

If then set the idle speed screw such that the throttle blade sits a little more then half way into the transition slot in each side of the Carbs throttle plate.

Next bolt the Carb on and fire the motor back up.

If your idle is still too high then you either have a vacuum, or the Carb is set up for too much idle bypass air,or you have too much timing or some combo of all three.

Also first make sure your throttle linkage is not keeping the Carb from going back to idle.

[track73]

Well Steve it idles down after it warms up so why would I think it has something to do with what you said? I'm confused. It passes emission here in Northwest Indiana with the single idle test so the carb seems to be ok after it gets heated up. I guess I should have mentioned that. It Idles around 750 when warm. Thanks for the reply.

[Kenth]

Sounds like you need a new choke pull-off?

At cold start after setting the choke closed the choke pull-off should open the choke blade .190" or so measured at rear of blade.
And. as the blade opens the fast idle cam lowers reducing the rpm´s.

[Dick Boneske]

You need to simply adjust the fast idle screw under the choke linkage on the passenger side of the carb. This is hard to see, but with a flashlight and medium sized screwdriver, it is not difficult. Let us know how it works out.

[Mister Pontiac]

Originally Posted by Dick Boneske

You need to simply adjust the fast idle screw under the choke linkage on the passenger side of the carb. This is hard to see, but with a flashlight and medium sized screwdriver, it is not difficult. Let us know how it works out.

Agreed.

[Greg Reid]

Originally Posted by track73

I have fiddled with the fast idle screw and looked at the linkage and nothing seems to be out of order.

Seems like he already did that.

Sent from my moto g(6) play using Tapatalk

[Old Goat 67]

Originally Posted by Greg Reid

Seems like he already did that.

Sent from my moto g(6) play using Tapatalk

Fast idle on pass side or drivers side?

[steve25]

Sorry for my winded exhalation , but in general most folks with Carb issues do not have a known baseline to start from, so what I posted is what would have needed to be done.

[Old Goat 67]

Originally Posted by steve25

Sorry for my winded exhalation , but in general most folks with Carb issues do not have a known baseline to start from, so what I posted is what would have needed to be done.

You're not at fault here.

[track73]

As Desi would say to Lucy. "let me splain". I have driven this car for a while,with a Holley 850 without a choke,the original Qjet with out the choke. and another Chevy carb without the divorced choke . I liked the Holley, but I wanted a little better gas mileage and starting ability.So I finished putting Cliffs jets,springs, idle tubes, metering rods,choke pulloff, needle and seat and accelerator pump. It an just great and passed emissions with flying colors. But it needed about 10 minutes to warm up so it would idle enough to drive. I had 2Eclin electric chokes lying around that worked the last time I used them so I installed one it on the "Cliffs Qjet" and it started great. So after I set the choke it would idle around 2000. I would then hit the gas again to drop the idle and it would stall. If I wanted to drive it I would have to play with the gas pedal to keep it running until the tem gpot to about 140. Then it would idle down. I have turned the fast idle screw up down sideways and nothing improved the situation. I am not a novice and have been working on carbs for many years but I may have forgotten some stuff.

[Joe's Garage]

The choke is only on ALL-THE-WAY when you first start the engine. The pull-off immediately opens it partially to give the engine the needed air so it's not sucking straight fuel.

When you first start it up COLD, the choke pull-off should pull the choke blade open about .190" measured at the back top edge of the blade to the choke tower. This only takes about 1 second.

If it opens too far, it makes the mixture way too LEAN and the engine stalls. If it opens too little, or not at all, the mixture is way too RICH and the engine stalls.

You adjust it by bending the link in the choke linkage to make the link shorter or longer, depending on which way it needs to be adjusted.

Once you verify that the pull-off is working correctly, THEN adjust the high-idle speed with that hard-to-get-to screw.

You don't have to check this with the engine running. With a COLD engine, push the throttle down a little so the choke will set FULLY closed. Hook up a vacuum test pump (or just use your lung-power) to apply vacuum to the choke pull-off thru an extra piece of vacuum hose.

The pull off should contract and the link to the choke mechanism should function and pull the choke blade open that .190" or so. I think the original specs called for it to open enough for a 3/16" drill bit to fit in there between the choke blade and the back wall of the choke tower. Later GM specified what angle the choke blade should be at and sold a tool to check the degrees of the choke blade angle.

If the pull-off doesn't contract, it's bad and needs to be replaced. They're usually about $10-$15.

If the pull-off contracts but the choke is still fully closed, the linkage needs to be adjusted to get the choke blade to open about .190".

Here is a link to an article explaining it all better, with pictures showing the drill bit adjustment procedure:
https://www.hemmings.com/blog/articl...ke-adjustment/

Good luck!

[Old Goat 67]

VERY good Joe!

[track73]

Thanks Joe!

[Joe's Garage]

If the choke blade opens TOO FAR when first started, or when you are checking with the engine COLD and OFF by applying vacuum to the pull-off, you need to either bend or straighten out the link to keep the choke blade shut more.

Aim for that 3/16" gap at the top rear.

[abefromen]

https://www.chevelles.com/techref/Ad...tic_Chokes.htm

[track73]

Ok so the fast idle cam is synchronized with the choke opening. So when I tickle the throttle and it doesn’t go to the next step, that has to do with the choke rod length?

["QUICK-SILVER"]

Originally Posted by track73

Ok so the fast idle cam is synchronized with the choke opening.

In sync with choke closing. When the pull-off or heat opens the choke....Gravity makes the fast idle cam fall down. A tab sticks out of the stat choke linkage and lifts the weighted end of the fast idle cam.

Crack the throttle open and work the top (weighted end) of the fast idle cam with your finger. See if it's sticky or in a bind. Throttle cracked and choke open the fast idle cam should flop easy easy up and down. As in no resistance at all.

Clay

[track73]

My concern is not that it (fast idle cam)doesn’t fall down.It is that it falls down too far. It goes to the last notch and not at the 12-1500 rpm and the engine stalls. I guess I’ll remove the carb and recheck everything. Don’t forget the shaker assembly can be a PITA to remove and replace all the time.

[1968GTO421]

Try this for good info on chokes:

https://www.chevelles.com/techref/Ad...tic_Chokes.htm

(Shurkey posted this on another thread which I couldn't find but since I had printed it out for personal use, I just searched for the original article; it's really good.)