I have a 71 Buick w/Rochester 7040244 w/divorced choke. I have had the Carb rebuilt twice....by reputable guys. One rebuilt it to factory specs-installed accelerator pump that fell apart after a week(guess the new gas doesen't work well with origional parts!) and removed the epoxy sealing the plugs causing leaks...guess that was a bad investment. The second guy fixed the above but did not get the choke and fast idle right. I can't continue making the trips to get this fixed so it's either do it myself or buy a new carb....when I get the $$. So..when you hit the gas when cold or pull on the throttle the fast idle does not engage and the choke plate wll not close. The push rod from the stove box is set at the proper height. You can enage the choke if you push up on the linkage (have to apply a little force). What adjustments can be made??? I think there is a problem with the fast idle cam?? I'm stumped. Thanks-
Check to be sure some part of the choke isnt binding or sticky. with the thermostat disconnected does it actuate properly by hand? It should "snap" closed when the throttle is opened on a cold motor, with the thermostat rod connected. so without the rod connected the whole choke system should move quite easily by hand. Verify all the choke adjustments as detailed in the service manual. post some pics of what youve got.
Does not snap closed-wish it did. It does seem like it is binding-just don't know if there is a typical "problem" area I should look at. When you do set the choke manually the fast idle will start to rev up way to much as it wrms up instead of slowing down...grrrr. I will try to get some pics tonight.
Just a couple of observations. When the motor is cold and off. Open the throttle and the choke should snap closed. If it doesn't either the linkage is binding or the choke spring itself is bad. You should be able to hold the throttle open and see what is binding. If you take off the choke rod you should be able to move the part it is hooked up to freely back and forth IF YOU HAVE THE THROTTLE OPEN. Most peaple forget that to get the choke to set you have to open up the throttle. As to it reving up after setting the choke and warming up. That is normal. Unfortunately that is the nature of the beast. If you get it set that it will idle stone cold on the choke it will rev up to almost 2000rpm when it warms up unless you "blip" the throttle to drop the fast idle cam down. It is a fine line to get one of these adjusted close. Just remember that this is not a fuel injected motor. Carbs as they warm up do not run perfectly. Mike
I just looked at the chassis manual for the card-about 500 adjustments to get the choke adjusted right. No wonder it's hard to find a good Rochester tech! I have no clue where to start. Unfortunately I don't think it's something as simple as the linkage gummed up or binding...but I'm going to double check. BTW-it takes a multiple of "blips" to get it to curb idle after warmed up. The chassis manual adjustments are intimidating!
Let's look at this from a systemic standpoint. First, the choke must completely close on a cold engine. This requires two things: One is that the coil contracts, RAISING the link from the manifold. Two things are possible here. One is that the coil is defective, not contracting sufficiently to raise the link. The other is that it is incorrectly installed, causing the coil to pull the link down instead of up. Try this: with a WARM, not hot engine, try spraying the coil with carb cleaner. Do this with a warm engine so you don't start a fire. When the coil is hit with the choke cleaner, it should contract, raising the link for the choke. One other thing to check is that the choke is free to respond to the link. Open the throttle slightly, and try moving the choke blade by hand. Tw things should happen. One is that the choke blade should move freely, and unload in the open position. The second is that the fast idle cam should follow the choke blade. One other thing to check on the choke coil is that the cover is intact, and that the coil is wound so that when it contracts, it raises the linkage for the choke. The link should be free to move in the housing, and it should be vertical when it contacts the choke linkage. I have seen both the linkage being improperly connected and the housing binds the coil. Look for both. Let me know, and PM me if you like. Once we get the choke to close on a cold engine, the rest of the adjust,ments are intuitive, once you understand their function.
YES! I started looking at the linkage from the throttle side to the heater box side and was able to see a coiple of places that were binding plus the link was rubbing up against the side of the stove box. Cleaned it up and made some minor adjustments and everything moves freely. I'm going to see what happens in the morning when it's cold. Almost there. Didn't realize the choke affected the overall performance of the carb. Thanks for the input-I'll report back once I've tweaked it. Beats taking it to a "pro" to fix!
I feel your pain...My choke closes properly and does everything except coming off fast idle. it doesn't like to step down and I have been struggling myself. I bought Cliffs book to get a better understanding and hope it helps me find the problem. I was thinking linkage is your problem as well.
I have posted this previously, but I am happy to repost this. Once the engine is cold, the choke, when the throttle is pushed down about 1/2 way and released, should do two things. The choke blade should close completely, and offer some resistance to being pushed open with the finger, and the fast idle cam should come under the throttle linkage, inhibiting its full closure. This offers the fast idle which keeps the engine running cold. For the record, a normal choke closure should start to close the choke when the engine has been sitting more than four hours. This should present as a choke not fully open when you remove the air cleaner. The closing pressure discussed prevents the choke from partially unloading while cranking the cold engine. Once the engine starts, it must breathe immediately, or it will cold flood. This is the function of the choke pull-off, or vacuum break. It will pull the choke open about 1/4 inch when measured between the choke blade and the rear of the choke housing. This adjustment provides two things. One is that the engine, when cold must have just enough air to prevent hesitations when lightly accelerated right after start up. Once the engine is running steadily, its idle will rise slightly when ready, tapping the throttle slightly will drop the idle, but not to the point of stalling. If the engine hesitates when driven gently cold, the vacuum break should be adjusted slightly richer, or for less opening when the engine starts. Once the engine responds well to the choke, the fast idle can be adjusted to a lower setting IN SMALL INCREMENTS, and reevaluated the following morning. You will know it is right when it still feels strong enough to keep the engine running when put in gear, but not so fast that it feels like a cat shot when the brake is released. Once this setting is satisfactory, the choke "duration" can be set. This is done by driving the vehicle during warm-up. Normally, once the engine has been running about two minutes, the effect of the choke pull-off no longer applies. From that point, it is the time the choke stays loaded that determines the engine driveability. If the engine hesitates when the throttle is gently applied during warm-up, tighten the adjustment, either by rotating the choke cover in the housing to the richer position, or by lengthening the link coming from the divorced choke housing, in small increments. If the engine does not hesitate during warm-up, the choke is either set properly, or slightly rich. If is appears that the choke takes forever to come off, indicated by a fast idle that never drops to normal, or takes forever to do so, try leaning the choke, again, in small increments. If nothing seems to work here, it might be necessary to check the heat coming to the coil, as it might be either weak, or non-existent. Next posting: Testing choke coil heat. Hopefully this will help.
Ray-if the choke plate does not close completely and the fast idle cam is not engaged what adjustment should be tried? I thought I had it right when the car had been sitting for 4 or 5 hours-the choke plate closed completely-fast idle engaged etc. Left it like that and cranked the next morning and the vacuum engaged but the choke did not open and it stalled(no air is a problem!). Got it going and ran fine. Next morning the choke closed all but 1/4 inch but the fast idle did not engage. It warmed up but now seems to be running rich!o No: Not giving up!!
First, let's make sure that the choke is closing completely. The next morning, when you get a chance, with the engine overnight cold, set the choke, but do not start the engine. Remove the air cleaner cover, and check the choke blade. If it is not completely closed, check the coil for free movement, and adjust the link to close the choke all the way. Two things may be happening here. One is that the coil is not closing the choke, or the fast idle cam is not allowing it to close. I suspect the former (the choke coil.) Frequently, the coil loses its tension, and either refuses to close the choke, or, if tightened sufficiently to close it, it will not open the choke. This will require the replacement of the coil, which does not surprise me. Let's not mess with anything until we have the choke closing. Unless it closes, the fast idle will not work, and messing with it until it does will cause other problems. Let me know...
It is getting closer. It closes completely when cold, starts good and the fast idle is engaging. Made a slight adjustment to the bend in the rod. The only thing is the secondary pull-off is not opening the blade as far as it should be(1/4"?) so I think we need to adjust the tang on the connecting rod so it will pull it open a tad more. Have another question. What would cause the secondaries to lock-out(not engage) at WOT. It seems to be sporadic. Thanks for all the help!! Chris
First, with respect to the secondary choke pull-off, try running without it if possible, Its only purpose is to control cold emissions by pulling the choke further open when the air cleaner temp reaches about 100 deg. Great for emissions, not so good for driveability. It is possible to adjust it for no effect; I suggest that, if it is necessary for the air valves. I am not sure how yours is set up, if it has both choke pull-offs, try using only the one on the front; it controls the air valves in the typical set-up. With respect to the secondary throttles, normally erratic performance is the result of the choke not opening completely. It may look open on the choke blade, but if it is not completely open the lever on the pass side of the carb, near the link for the secondary throttles will not rise sufficiently to clear the stop. The result will be secondary operation if you hold everything just right.
Re: Choke-I'm stumped/Dumb and Dumber Got the choke to work-warms up great, fast idle steps down, great response off idle but secondaries STILL stuck. So...remove the secondary lockout at the top-that has to work. Nope. Secondaries wont open. I finally tuck my tail and take it to a a guy who could build an old Buick in his sleep. He looks at the carb, pushes on the secondary choke plate, says hmm and then pokes it real hard with two finger and says "fixed". Runs great. Felt pretty dumb but it works-plus he didn't charge for the two finger fix. :grin: Thanks Mike!:beers2:
