I have a Carter 750 Comptetition series on my freshly rebuilt 350. Poston Intake, GS114 cam, 10.2 compression motor. We've been messing with the carb for a week, just rebuilt it, and can't kill the hesitation off the line. The timing is set at about 9* (which I think is high for this motor) and the car will deisel after you shut it off like this. We have the car idling at about 800 RPM out of gear, when you set it in gear it falls to 600 and then will slowly die if you don't give it gas... We've set up the carb at the recommended starting points, but can't seem to get the thing to act right. Any carb-savvy people out there care to shine some light on the situation? Thanks in advance...
Chris, There is an excellent book on all Carter carbs. It is Super Tuning and Modifying Carter Carburetors, by Dave Emanuel, SA Design Books ISBN 0-931472-11-3 Are you sure on the rebuild? Sounds like the idle system is lean for some reason. How does the exhaust smell? Lean or Rich? If it idles out of gear at 800, it should not run on. Are you sure of the float levels. If they are set too low, it will run lean at idle and off idle, and give you hesitation. Hope that helps.
Chris, you might be running too much carb. It sounds like you have about the same set-up as my wifes '67, I put a 600 cfm Carter AFB on it and ran 13:90's right uot of the box.:Brow: I started playing with the jets and rods after that, and lost time.ou: Now it is back to orig. set-up for spring! Just something to ponder:grin: :Smarty:
After having no luck with the Carter, we just put a Demon on there and although it killed the problem with the car dieing in drive, it still has a slight hesitation and just doesn't pull as hard as this setup should. My 106k mile never-rebuilt GS350 runs this hard, and I try not to do that. Boy, this is getting to be too much fun :af: . I'm not a carb man by anymeans, and it looks like I may be reaching the end of my rope. The car won't idle consistantly (it idles at around 800, but fluctuates 50-100 rpm constantly) and in gear, it will idle between 450 and 650. I'm running what shows to be 11* advance, but the Demon book says these carbs like as much as 18*? Does that sound correct? Maybe I'm stuck in my ways, but I always figured for something that will be street driven you stick around 6-8*. Still lost in the woods....
Chris, Have you checked the mechanical, and vacuum advance for proper operation. Is the timing advancing as you open the throttle. I haven't seen the Buick motor that doesn't like at least 12* initial. The only thing you need to worry about is over advance at higher RPM. If you move up the initial and shorten the mechanical advance so that total is 30-34* at 2500 RPM, it can make a HUGE difference in idle quality and low end response of a cammed engine. I run 16* initial, 32* total at 2400, and 10* full manifold advance. The car idles at 700 in gear at 26* timing. Throttle response is lightning quick. Check your timing, recurve or repair. It can make the difference. I still think your AFB is too lean.
I agree with Larry about the distributor, also check it for endplay, I had one in a 350 with too much slop, wouldn't run good, shimmed it up, then it really started pulling. Also, what are the specs on the cam? Are you running a high stall converter with it? Also, I'm not familar with your particular carb, but with a larger cam(less vacuum), I used to trim the little springs that control the rods (you can probably order a lighter tension) also I've drilled two small holes in the primary butterflies to help the idle (extremely small bits must be used, can't remember the size, but you can hardly see them).
9 times out of 10 surging idle speed is a vacuum leak. Seeing that you went from a Carter to a Demon and the surging is still there I would look for a bad vacuum hose or intake manifold gasket. You rebuilt the engine so double check the manifold gasket. Did you get a vacuum reading with a vacuum gauge? If you did what was the reading? Even if the initial timing was of a bit the engine won't surge at idle.
I would have to agree with everything, check your vacuum and also what the idle mixture is like. don't be afraid to richen it, but a puffing exhaust is too much!! I'm not at all familiar with Carter carbs, but on the demon anyway you could try upping your squirters to cut back on the hesitation. Also, going to about 2 sizes jets bigger may help, but I'd read your plugs (time slips more preferably) on that. If you still have a hesitation you should think of a bigger accelerator pump or even changing your accelerator pump cams. the hesitation is the worst to get rid of and I have found that it is usually a sign of a "lean" bog. Better to go rich than lean, IMO
Balance this equation: Carb CFM= (engine CID xMax RPM)/3456 650 cfm Carb would be more appropriate for your application.
Larry is right with his recommendation. Here is what's happening, you don't have enough initial timing, so to get the car to idle (in park) the throttle blades have been adjusted too far open and now at idle the blades are at a part throttle condition which is actually causing a vacuum leak right down through the primaries themselves. There are a few things to check when setting it up. First put your initial timing at 12 to 16 degrees (for now don't worry about total). Your RPM will increase, lower the idle RPM by turning out the throttle screw until you get a good idle (in park). Now put the car into drive, it should drop no more than 100 RPM and idle with out problems. If it does, your on the right track. If it doesn't then you need more initial timing. Continue doing so until you get that good idle in both park and drive. To confirm that you are getting the carb/timing set up properly, take a vacuum reading from the ported vacuum port. It should read zero at idle. One port will have vacuum at idle and one should be zero. If the one port is still not zero continue adding initial timing. A 750 carb will work fine, the reason the smaller carb worked better is because it is a restriction, thus a better vacuum signal. As a disclaimer, because multiple things have been changed, if you find that it needs 20+ degrees at idle then you may benefit by advancing the CAMSHAFT more to tighten up the power band. Ok, once you determine the best initial timing, take the distributor to a shop that can re-curve the distributor. Re-curving is more than just weights and springs. Give them the initial timing that you found worked best, then have them set the total around 34, and have it all in around 2700 RPM. You will need a dial timing light to check all of these settings, it will be the best $80 you ever spend on tools. With all of this done it should idle nicely and have good maners when going from park to drive. You should have crisp throttle response and no hesitiation. If you have performed the distributor curving and it still has some hesitation then it is lean. First take a vacuum reading at idle and make sure you have the right spring combination for the primary rods. Correct if necessary. If you still have a hesitation begin to change jets and rods until it is just rich enough so there is no "bog"/hesitation. Dave
Dave (and others) I really appreciate the good tips. This stuff all sounds like rocket surgery to me, so the detailed advice is definitely helpful. I was talking to Phil Green (TXGS) the other day and, stupid me, I forgot to mention that two lifters aren't pumping up. This would effectively kill two of the cylinders, and most likely the big part of what is causing my hesitation. From what Phil said, this will cause the idle fluctuation and make the car hard to time and tune. It looks like I will be taking the intake off and rebuilding a couple of my lifters. But no doubt this advice will be put to use when I get it running strong on all eight cylinders.
