86 305 idles rough on cold start, ideal when warmed up

[ilduce]

My 86 GP starts all the time. If on the same day as it's been driven, turn the key and it has the best idle of any G-body with a V8 I've had (three before this one). Sure doesn't like to sit. After a couple days you have to do the Ivan Pumpski and in seven seconds it'll be running, but rough like a top fuel dragster. I checked the choke. It doesn't close all the way when set. It's open about a quarter inch, there's a little slop on the link that goes up and down and attaches to the plate swivel. But, the choke opens up nicely after a few minutes. Still, it idles pretty rough for a little while. If you try to stick it in gear and go, it'll die. But within a few minutes it'll start idling nearly perfectly. And, not gradually but all of a sudden. I just wish I could hear it coming and figure out what the hell is making it do that. If it just snaps into perfect idle mode like that, shouldn't it do that automatically a lot sooner when it's cold? Or, is this just normal behavior on a cold start for an electronic Q-Jet?

I'm not familiar with all the electronic gadgets on the carb and associated with it. Every stinkin vacuum line is new, but none of the control modules or anything else with a wire coming out of it on the carb. I should mention there is no cat. There's dual pipes going from the manifolds back, so I can imagine it won't idle like new but when warmed up it's ideal. The AIR pump is there, still has lines going to the manifolds. After it idles nice, it's got good response. No hesitation or carb burping or missing. I don't even think it's worth doing plugs it runs so well. I floor it on the entrance ramp and the sound reminds me of Bo and Luke.

Any ideas? Total carb rebuild time? One of the electro-gadgets? Forget it and be happy it runs nice after warmed up and get a case of Molson?

 

[olds307 and 403]

Sounds like the choke pulloff is shot or needs adjusting. Get a new front pull off and I bet that will fix it. In warm weather the choke may not close completely, mine does not. In cool weather, it should.

 

[billyjack]

Set your choke so that it is just barely closed at about 60 degree air temp. Adjust the front vacuum break to open the choke about 1/8 inch, secondary break about 1/4 inch. That should put you in the ballpark. I set my 87 305 up that way and it fires quicker than any of my later model injected GM cars.

Bill

 

[ilduce]

Set your choke so that it is just barely closed at about 60 degree air temp. Adjust the front vacuum break to open the choke about 1/8 inch, secondary break about 1/4 inch. That should put you in the ballpark. I set my 87 305 up that way and it fires quicker than any of my later model injected GM cars.
Bill

I'm sure what you're talking about is helpful, but (as I said) I'm not good with carbs. I can rebuild them and somewhat get the pieces to go where they probably are supposed to go, but I need a little better clarification as to how you do what you are saying to do, and why I should do this (don't worry about using simple terms and offending me, if I knew more about carbs then I wouldn't have needed to post this).

 

[ilduce]

I went out this morning to play around with the choke and the front pull-off. There's no secondary vacuum break. But, the front pull-off is there. I don't know how to see if it's working right or adjust it. The only thing that seems intuitive would be to adjust the screw the black arrow in the picture is pointing at. But, what does it adjust? If I turn the screw one way or another, what will it do? The screw isn't touching anything, so it can't be for adjusting clearance.

I'm not completely understanding how the front pull-off "pulls off" the choke. There's no mechanical pieces that I can see that attach to the choke lever or rod. The only thing I can see mechanically doing something is the link that goes to the secondaries. If I pull the secondary plate open, the pull-off will close em down again; doesn't seem to do anything with the choke though.

Should I just buy a new pull-off and forget about this mess?

 

[billyjack]

The machine screw your arrow points toward threads through a small link that opens the choke when vacuum is applied to the actual diaphragm. There are cams and links in between the choke housing and the carb body that control fast idle and choke opening.
Here's the adjustment procedure I use.
First, set the choke thermostat. With the engine off and throttle held open, loosen the three phillips machine screws that surround the black plastic choke cover just enough so it can be rotated. Rotate the cover so that the choke blade just barely closes at 60-70 degree air temp. Tighten the screws.
Second, adjust the vacuum break. Open the throttle momentarily to let the choke close. Ideally, you want to apply vacuum to the round vacuum canister just forward of your arrow, using a handheld vacuum pump. In the absence of a pump, push the machine screw forward, retracting the plunger into the cannister until it bottoms. Note how far the choke blade opens. Adjust the machine screw until the choke blade opens about 3/16", using a drill bit as a gauge. Start the motor and immediately check choke opening with your drill bit. That should put you in the ballpark. You can fine-tune from there depending on how the car feels. Good luck and don't hesitate to post if I haven't explained it well enough. I do believe your '86 motor should have a secondary break, but maybe it was removed by a previous owner. No big issue, since many other GM applications only used a single break. With a little tinkering you should be able to get it dialed in pretty close even with just a single break.

Bill

 

[ilduce]

don't hesitate to post if I haven't explained it well enough.Bill

I can follow that advice! Good thing I didn't stick a Mr. Yuck sticker on the carb and call it quits.

But, one more thing! How would I remove the choke rod without taking the carb off the engine?

I may not have to adjust the choke because the slop at the choke rod and upper lever is what's keeping the choke plate slightly open. The choke closes all the way if I push it down. My service manual says to push the rod straight down when the choke is set. It says the top of the rod should be mated at the lowest part of the choke plate lever. When I do that with mine, it's set all right. I can't push the rod down, it's set. But, there's this slop at the lever, as if the choke rod is a little too long, allowing the plate lever to float around too much. Well, I'd like to shorten it. The service manual says to shorten it until it's ideal, but gives no method of doing it!

So, I can take the rod out and try to custom bend it or replace it with something I made, like out of copper wire. The top part looks easy; at the lever on the choke plate. I can unscrew the lever retainer screw, take off the lever, and take that off the rod. But, I don't know what the choke rod attaches to at the bottom. I think it's behind the choke thermostat assembly or inside the carb wall. I can't see down in there to figure out how to get the rod off at the bottom, so I'm really not sure how I'd get it back on if it came off!

Or, can I use pliers to bend it so that it acts like it's shorter while it's still on the carb? If I could slightly bend it that would reduce it's overall vertical length and maybe do the same thing as a shorter rod. Can it be bent without breaking? I really don't want to pull the carb off to make such a petty adjustment. After that I could adjust the choke like you said with rotation.

 

[Bonnewagon]

Don't touch that rod. It is a b*tch getting it reinserted into the lever at the bottom of that well where the choke shaft comes through. One day when you are bored you can remove it and try replacing it for laughs, it is a skill. Just do as Billyjack says. The slop will not matter. The flap will close properly if you adjust the housing as advised. There is a bi-metalic spring inside the housing that winds/unwinds according to temperature. Set it so it closes the flap when cold. As it heats it will open all the way. The vacuum choke pulloff on the front of the carb will open the flap a bit to allow it to run well as it warms up. Measure that as Billyjack advised, it is critical to smooth operation.

 

[olds307 and 403]

Problem with no having a secondary break is the secondaries will probably not work right. Probably a bog on hard throttle.

 

[ilduce]

Don't touch that rod. It is a b*tch getting it reinserted into the lever at the bottom of that well where the choke shaft comes through. One day when you are bored you can remove it and try replacing it for laughs, it is a skill. Just do as Billyjack says. The slop will not matter. The flap will close properly if you adjust the housing as advised. There is a bi-metalic spring inside the housing that winds/unwinds according to temperature. Set it so it closes the flap when cold. As it heats it will open all the way. The vacuum choke pulloff on the front of the carb will open the flap a bit to allow it to run well as it warms up. Measure that as Billyjack advised, it is critical to smooth operation.

Cool. I'll keep my hands off! I also found out there was never a secondary vacuum break on mine, the one in the front is the whole deal and works 'em both.