Hello, Back into the Buick fold after several years... Car is a 1970 Skylark, 350 2-bbl. It has a rough, shaky idle that makes the windows and dash rattle, and the bumper/grille shakes up and down. Kind of shakes back and forth from back to front, etc. But when the idle goes up, everything smooths out, so I raised the idle speed slightly. Now only does it in drive or reverse. It accelerates perfectly, and fast too, but starts shaking when coming to a stop. Also, when cold it tends to start right up, but then sputter and stall after about 5 seconds, does this several times before staying running. I checked most vacuum lines, they all seem ok, but the butterfly valve on top of the carb is stuck in the open position, can't be moved by hand. Could this cause the rough idle? It does not seem to be temp. dependent, does it all the time.
as far as the shaking, check your harmonic balance, i had mine slip and it was way off where it should have been. once it hit a certain rpm it smoothed out but at warm idle it would shake like a wet dog, after i replaced it, it was like night and day. the start and stop problem is probably carb related?
i was able to spin the outer ring with my hand, if it moves a bit then it needs to be replaced or rebuilt. if thats the case change it asap and try not to drive it, if it slips all the way off you in for trouble
Interesting, I don't think it's the factory balancer, or at least it doesn't look like the ones I see on the web. What I think is the balancer, appears to be a thin disk with holes drilled in it, like a cross-drilled brake rotor. I didn't have a chance to run it yet to look, will do so when the weather clears up. Are there aftermarket balancers that don't resemble the factory ones, or am I looking at the wrong pulley (the one farthest at the bottom)? Does anyone have a pic of the balancer on their engine?
im pretty sure you have the right thing, you dont need to run it to see if its slipping.. this is not the correct balancer for a 350 but it lokos very similar http://www.taperformance.com/proddetail.asp?prod=TA_2026&cat=178
Yup, that looks like the one on my car. I will try to run it later after work to see if it wobbles at all
I tried to move it by hand, it does not seem to be loose but I did notice that the rubber ring in the middle seems to be pretty eaten away, hmmmmmmmm...
OK, I was able to drive the car yesterday when the weather cleared up. Does not appear to have any wobble in the balancer, although the rubber in the center looks like it's disintegrating. One new thing I noticed is that if you shut it off for a few minutes and then restart, it idles strong for about 5 seconds and then the idle goes down and starts shaking/surging/idle speed going up and down and making a lifter-type noise. All goes away when revving and/or accelerating. Also, the lifter-type noise doesn't happen when the engine's cold, starts after about 10 minutes, but it always shakes at idle, even when cold
I would recommend starting with the basics- cap rotor, wires, points, condenser and wires. Check the timing and adjust the mixture on the carb. Go thought the basics FIRST. Start at step 1 not step 5. Sound like you might just have a bad vacuum leak. Put a vacuum gauge on it and see what the reading is.
That flap on the carb is your choke, if it is stuck open and won't move, then your choke for cold starts is not working, explaining your cold starting, wont stay running issues. To check for vacuum leaks, while the car is idling, lower your hand slowly over the top of your carb, if your idle speed increases when your hand is close to covering it, you probably have a vacuum leak somewhere. When you cover the top, it should stumble and die out. Tune it up with new plugs, points condenser as recommended, and then adjust your air/idle screws on the front of carb for the highest vacuum reading or idle speed. Since it runs good otherwise, those things should smooth it out for you. Hope this helps. Good luck.
OK yesterday I had it out and briefly put a rag on top of the carb, the engine nearly stopped when I did so, does that rule out a vacuum leak? Also, played around with the idle mixture screws, but I may have to fiddle with it a little more. Turned both in all the way until seated, then back out 2 1/2 turns. When I did so, it wouldn't start until I turned them out a little more. Seems to run faster the more you turn the screws counter-clockwise, but I didn't want to loosen them too much. Ran out of time, but it pretty much ended up the same as before. Will have to check the plugs, etc. next
when you tune a carb your suppose to turn the screws for the highest rpms or highest vacuum reading, so if it was going up the way you were turning it weep turning it untill it starts to go down, and then turn back the other way to highest vacuum or rpm if you dont have a vacuum gauge.
Nope, put a vacuum gauge on it. Should be in everyone's tool box. They aren't expensive, and they can tell you a lot A stock engine fully warmed up should read 20" at idle, in Park
Brian350skylark, I've never done this before so I was being extra careful, I wanted to be sure that I did not turn the screws too far out that it falls out or something, how far will it usually go before that happens?
Another thing I noticed after going on a longer ride - the power brake booster seems to be barely working, feels like manual brakes - could that indicate some kind of vacuum issue inside the brake booster that may be causing this uneven idle quality?
