When I do a cold start, she fires up reasonably quickly (2 or 3 pumps, wait a couple of seconds, and then key it with the foot off the pedal), but runs very rough for 10-15 seconds and then almost invariably stalls.

:mad

Then, a struggle to get her started again, she runs rough, then smoother ... then OK. I've learned to let her run for at least 5 minutes or so before hitting the road, and then I'm good to go. On a warm start, she fires up immediately and smoothly.

There's got to be a modus operandi for getting her to keep running off the first start. Any insights on this would be appreciated.

 

I was having a similar problem with mine. Is your carb a Quadrajet? In that case, my choke pull-off diaphragm was torn. Your choke get your car to start and the choke pull-off as the vacuum built, crack open the choke to let breath your engine a little. It is located at the front of the carb at the passenger side. Check when you start the engine if the vacuum pull the diaphragm.

At least this is how it's made on my 1980. Hope this help.

Stephan

 

Mine used to have that problem too. I'd have to give it a little gas to keep it from dying and then it'd be fine. Also had some problems with what I assume was moisture in the exhaust. My car is parked outside
:cry so when the hot pipes cool overnight, i think moisture would get in and make it harder to start/run. so I just make sure my car cover covers the exhaust pipes to minimize moisture.

I would say check the obvious things: make sure spark plugs/wires are still good, timing is right, etc. Haven't had too many problems starting up after i tuned up my car(with a little help from my uncle :yesnod: )

 

Adjust your choke...it needs to be set Richer, and/or the fast idle screw needs to be adjusted to increase your idle. An idle of 1,000 - 1,200 is common when cold.

 

Thanks. I'll look into those possibilities.

 

Yes, my carb is a Q-jet. I described this scenario over the phone to my mechanic, and he diagnosed this same problem.

I'd be interested in some views on the "degree of difficulty" of this issue. As I indicated on another recent thread, I'm a complete novice with no skills and no tools. Any chance I can fix this (with the knowledgeable input of this Forum), or should I just open my wallet?

 

Should be very simple...the choke spring is located on the intake manifold on passenger side of carb...the housing pops off revealing the spring and screw. Fast idle screw is located in that area as well on pass side of carb.

Just a thought, but have you tried to hold the pedal down about 1/8 of the way...it will help trouble shoot...holding the pedal down...or just tapping it just after it's started will cure a problem of the choke linkage binding...in which case spray some WD40 around the choke linkage.

 

I could guide you trought the process, I just got a digital camera that could give some good picture of it. It is very simple to do. We just have to check if it is the real problem and after it is a matter of ordering the right part and installing it on the car (2 screws). If you can wait till saturday, I will be glad to help (I work 12 hours a day till then).

Stephan

 

Stephan, thanks. Let's get in touch on Saturday.

If anyone else wants to pipe in on this issue with some tips, please do.

 

American Boy is right. If it is the choke pull-off it is one of the easiest fixes you can make on a Quadrajet. I just rebuilt mine last weekend and have become pretty familiar with its operation. :D
You can test the pulloff with a vacuum pump but don't worry if you don't have one. Take the vacuum hose off the back of it and attach a longer (2 ft.) hose, preferably a brand new one because you are going to suck on the hose to create a vacuum. You will see the pull-off literally "pull-off" the choke. (This is a really clever name don't you think?) If it doesn't pull-off, replace it. You just saved yourself a $50 labor charge. :D

 

OK, thanks, I think I can follow that. A couple of questions: (i) When I go to the auto parts place, how do I ask for the hose? ("Er ... I need a hose to suck a vacuum outta my choke pull-off thingy"); and (ii) What if, when I do what you've suggested, it does, in fact, pull-off the choke?

 

Take the short hose off the pull-off and bring it to the autoparts store. Buy maybe 2 feet of it. It is a very standard size and many of the hoses connected to the carb are this size so you can always put it to use later. If the choke pull-off pulls off, then you have eliminated that as a problem. You can also check it by haing someopne else start the car and watching the pull-off afater the car starts to see if it is working.

 

If the choke pull-off is working, there is also an adjustment screw near the top of the device. Turn the screw and watch what is happening and you will see that it adjusts the amount that the choke is being pulled by pushing back a cam. If this looks alright ,check to see if the choke is working. When you press down on the gas 1x and the car is cold, the choke should close the flap on top of the carb. If this all looks alright, then move to the fast idle screw. This keeps the car running at a faster idle until it warms and is kicked down. If your carb is like mine, the screw is well hidden under the choke mechanism and is adjusted from the front of the carb. It is hard to find and harder to adjust. Not complicated, just hard to reach. All these adjustments work together to make the carb work correctly. It is pretty hard to mess this up. Just remember where things are adjusted now and play around with it and get a feel for how the thing works. You can always just put everything back and bring it to a mechanic and let them mess it up.:D

If you still want to take this on, go to corvettefaq.com and get Lars' paper on tuning the Quadrajet. Also get a service manual or a Haynes manual will do, and it shows the basics of these adjustments. If you decide you want to know more, get Doug Roe's book on Rochester Carburetors.

 

Thanks for the detailed instructions. I really appreciate it. (I may not fully understand what you've written, but I appreciate it!)

Doing some further digging, I found a set of instructions at the Champion Auto website for testing the choke pull-off and installing a new one. It's a pdf file, tech tip #63 at:

http://www.championauto.com/championauto/techtips.html

Those instructions say that there's an adjustment that has to be made (distance between choke blade and housing) after you get the thing on, which require me to measure this distance with a gauge and then have a Hayes manual to know the car's specification, and then adjust it, either by turning some screw or bending a linkage (huh?). This adds a level of complexity that might be beyond my reach.

Sorry to be so dense about this stuff. As I said at the beginning of this thread, more or less, I'm an idiot.

 

Wow... that's strange. My car just started doing the exact same thing. I'm we have some ideas to pull from here...
:cheers:

 

When the choke sets (the flapper closes) they are saying to measure how tightly it is closed. Basically, it should be slightly open. The guage is slipped in next to the flapper (non-technical jargon :D) and this measures the opening. But if it is generally closed it should start. The idea is that the car gets a richer fuel mixture (more gas, less air), because that flap is cutting off the air. Once it starts, the pull-off pulls that flap open some, allowing more air to rush-in to keep the car running. Your problem though sounds like the car is either getting too much gas (because after the car starts, the flapper is not being opened some by the choke pull-off) or the pull-off is working and that fast idle screw I spoke of which was hidden by GM engineers so as to keep its location secret to the world, needs to be turned a couple of turns.

 

OK, here's the current state of affairs.

I tried to take the hose off of the choke pull-off, but couldn't. It's just not moving, at either end. Great, ... I'm a hopeless failure as a mechanic, right from the git-go.

So then, with the carb still exposed, I go to try to start the car. I tap on the gas to set the choke. I see the choke set. (There are three flaps on the top of the carb, and the one that I'm calling the choke flap is the odd man out, longer and narrower, closer to the nose of the car. The other two are like twins, and they're closer to me in the driver's seat. You'll have to excuse me for not knowing the technical terms here.)

I turn the key, and she turns over and starts up. She only runs for a few seconds before stalling, but during that time I think I see two things. First, I THINK I see the choke pull-off move. Second, I THINK that I do not see the choke flap move with it.

What's further confusing about this is that the choke pull-off does not appear to be attached in any way (directly or indirectly) to the choke flap. There's a linkage between the pull-off and the carb, but the thing that linkage is attached to moves the two twin flaps, not the choke flap. In any event, and I suspect this is important, when I manually move the business end of the pull-off, it has no effect on any of the three flaps on top of the carb. The linkage just moves back and forth inside the little loop that it's hooked into, without apparently causing anything else to move.

Dunno if the above is going to make sense to you guys, but I'd appreciate your views on it.

My battery is now dead from all the recent cranking trying to get 'er started, so I'm trickle charging it.

 

Good. That is in fact the choke flap. It sounds like everything is working correctly. The choke pull off does not attach to anything except by the 2 screws that hold it to the carb. It simply retracts and when it does it contacts a lever that pulls the choke off. The long rod that goes to apparently nowhere is for the secondaries - another subject altogether so ignore it.

When you look at the big black dial on the choke side you will see that it says richer-leaner. This controls the duration of the choke by winding a spring inside. Loosen the 3 little screws on the perimeter of that dial and turn it some toward rich - counterclockwise. Not too much. I also think your fast idle screw needs to be turned in some. That is the one hidden under the choke. If you take out the 2 screws that hold the choke pull-off on you can see it a lot better. Try giving that a couple of turns clockwise. That screw pushes on a cam that is attached to a rod that opens the flaps under the carb. (you can't seee them).

 

Sometimes a picture is worth a tousand words.



One things to check at the secondary airvalve; when the engine is not running, the rod that goes to the secondaries should be positionned as describe on the picture. You're on the right track, keep on.

Stephan



[Modified by American Boy, 1:03 PM 5/4/2002]

 

Well, I'm hoping that I've reached a resolution on this issue. I'm pretty sure that we're closer, in any event.

I spoke to a gearhead friend this morning and he agreed with the views expressed above. When I told him that the choke pull-off appeared to jump when the car was started, he thought that the choke thermostat probably needed to be adjusted (as you've indicated, R.).

He suggested that I get the car running and bring it out to his place to take a look at it, and he suggested a way to accomplish this. With my battery ready to go from the overnight trickle charge, I brought in my daughter as my trusty assistant. I got her to hold a coat hanger in place to keep the choke flap open just a bit while I fired it up. The car started right away, and, with the air coming in from the coat-hanger gap, ran smoothly while warming up. Once I got an even idle without having to put any pressure on the pedal, I took over the coat hanger. Eventually, after a few minutes, the choke flap opened on its own wider than the coat hanger, and I was able to remove the hanger.

I roared over to my friend's place, and he took a look. He confirmed that there's nothing wrong with the choke pull-off. He then showed me how to adjust the choke thermostat. We turned it clockwise a little less than half an inch from its previous position.

So I'll find out tomorrow morning, once she's cold again, whether than much of a turn was enough.

Another note for others who may encounter this problem, or even a failure of the choke pull-off. My choke thermostat is electric and doesn't depend on the engine's heat to open the choke. My buddy tells me that a work-around for this issue is to turn the key to the "on" position (i.e., the position just before ignition) and let it sit for 5 minutes or so. The car will be fooled into thinking it's warmed up, and the choke flap will be open enough to start the car smoothly -- essentially bypassing the choke pull-off and ignoring the fact that the choke thermostat is wound too tight.

Many thanks to R.Bruno and American Boy for the time they took in responding to my query on this point. I'll let you know how it turns out after the cold start tomorrow.

Thanks also for the pic. Unlike a couple of days ago, I can actually identify those parts now from direct personal experience!

Well, it's a beautiful sunny day in Toronto today, so I've got some road to tear up. Catch ya later.