I just picked up my first Buick!! Its a 1971 Buick Skylark GS 350 that I picked up from a kid that was in way over his head with it. Im having some issues with the engine. It has the factory Buick 350 in it and it had a crappy Holley 750 DP on it.. Way too much carb for the motor. I picked up a Edelbrock 650 AVS series carb but Im having some trouble figuring out the vacuum connections.. Im kinda green with carbs so be gentle... I have a large vacuum connection at the back of the manifold, there is the vacuum advance for the distributor and I have been told there should be a vacuum line running up from the transmission (Its an automatic) but I dont see it anywhere. Im having a hell of a time trying to find vacuum diagrams for this car. Can anyone help me out here?? -Cory
I would say that you are mistaken. From the factory they came with a 750 Q-jet and I would put it back that way. I have some 750s and they are readily available elsewhere. .
the vacuum diaghrams are located in a 71 chassis manual or 71 assembly manual.i am sure someone can scan and post.
hmmm.. All the info I found said that a 600 cfm carb was more than enough for a standard chevy 350 but with the buick 350 being a shorter stroke engine would require a 650 cfm.. I have nothing but horrible luck with holley carbs, so thats also why I made the switch to Eldelbrock.. If there is any chance someone could scan the vacuum diagrams for me or even just a heads up on where all the lines should go I would greatly appreciate it. Im assuming the kid I bought the car from might have hooked up the vacuums incorrectly before, because the car has always backfired through the carb at around 2,000-2,500 and hesitates really bad if I gas it too quickly. I was hoping the new carb might solve some of the problems but it hasnt.. I have noticed that the secondaries wont open up on the new carb, so Im assuming that I dont have the vacuums hooked up correctly. All the info Ive read points to a possible vacuum leak, valves being out of adjustment or the timing..
the chevy 350 , 1970 and probably onward, uses a QJ750 . that is what was on 70 malibu 350 4bbl (L48).
Cory, First thing is a Buick engine is not a Chevy engine. A 600CFM will cost you power, simple as that. Doesn't matter what the formulas say, throw that out the window, it doesn't apply. The best carburetor for a stock or near stock Buick motor is the Q-jet. It is an excellent carburetor for power and economy and you will be hard pressed to match it with anything in the after market. A double pumper carb is not a good match for a stock engine. It's not the total CFM, it's the mechanical secondaries that are the problem. Modified engines are another story. That being said, you don't need a vacuum diagram. It's pretty simple. There is a steel line coming up from the transmission vacuum modulator. It has a rubber line on each end. It goes directly into the intake manifold behind the carb on the passenger side. The power brake booster line goes into the intake on the drivers side rear. On the Q-jet, there is a large 3/8" fitting on the front of the carb. That connects to the PCV valve at the rear of the intake. The hose wraps around the carb on the passenger side of the intake. There is a fitting on the rear of the carb that goes to a vacuum storage cannister mounted to the firewall (it stores vacuum for the Heater/A/C controls) The front of the Q-jet has a ported vacuum connection, and a full manifold vacuum connection. The distributor vacuum advance normally gets ported vacuum. The full manifold vacuum connection goes to the air cleaner temperature sensor. That's it, done. It sounds to me like you have a vacuum leak. If you are trying to use a Carter/Edelbrock or Holley carb on your stock spread bore intake without an adapter, that can give you a vacuum leak. Get a vacuum gauge (they are cheap) and take a reading from the full manifold port on the carb. With the engine fully warmed up, you should have 18-20" in park.
also sounds like you could have 2 plug wires switched. ask me how I know. ou: i musta checked it 3 times drove it nearly all summer and occasionally had the pop. and had some wires switched.
Just like they said above. You have a Buick and the only thing it has in common with a chevy 350 is the numbers "350". What intake do you have? Are you having to use an adapter to put the Holley on? I have run Q-Jets on race cars and I'm building a Q-jet now for our 464 Buick build. They can work great. If you think you have a vacuum leak, put your hand over the carb top and see if the engine idle speed increases. If so, you have a vacuum leak. If it dies, no vacuum leak. Good luck.
Wow thanks guys! All that helps a bunch. I know the Buick 350 is a totally different block than the standard chevy 350 but I had read a few articles and talked to a few local HP parts shop guys and they all pointed to a 650 cfm being plenty for the engine. I have had nothing but great luck with Q-Jets on other cars I had in the past, but alas I have an edelbrock now and need to get it working. First , I checked the spark plug wires and they are all going to the correct cylinders. Second, I have checked the timing, points & condenser, cap, rotor, etc. and everything seems to be working fine. The car starts and idles no problem. Thirdly, all signs do point to a vacuum issue. I have the edelbrock 650 AVS Thunder series carb with an electric choke. I got the adapter for the carb to make it match up with the intake so there shouldnt be any vacuum leaks there. My car does not have power brakes or AC. I do not see the vacuum line coming up from the tranny anywhere, so that sounds like a problem right there? Also I have a large vacum sensor or fitting coming off the back of the manifold and I have no idea what that is used for? I was thinking power brake booster, which I dont have? The edelbrock setup for vacuums is pretty simplistic. There is the main vacuum port on the front of the carb. I ran that to the air cleaner. then it has 2 smaller vacuum ports on either side of the main vacuum port, one for manual and one for automatic transmissions.
Take a look under the car at the rear of the transmission. There should be a vacuum modulator coming out of the back of the transmission. There should be a vacuum line coming off of it. Where does it lead to? This is what a modulator looks like: http://www.v8buick.com/attachment.php?attachmentid=72381&d=1146602078
Okay, so I have an after market intake. (Im guessing a holley) The transmission line connects to a small vaccum connection at the back of the intake but there is no modulator connected to it. How important is this? I had a friend of my who is a mechanic come over and he mentioned as far as he could tell the vaccums were hooked up correctly. The car runs great now but Im still getting a very small hesitation if I get on the gas too quickly.
I think you need to take another look. Where does the other end of the vacuum line go? Is it just swinging in the breeze? The transmission will not shift without a modulator, and there would be a big leak at the back of the transmission if there was no modulator in the transmission. The intake should be marked with a manufacturer. If it is aluminum, it's either a TA Stage1, or a Poston S Divider.
i would take some pictures and post,it would be easier for the guys on here to point out whats wrong.!!!
