70 skylark 350 rough idle

I pulled out the booster check valve and the inside plastic part with the barbs is partially broken off, although the rubber grommet is OK. Will have to check into that.

 

Went for another longish ride to a cruise show today, doing the usual shuddering/misfiring every time I stopped at a traffic light - when I parked and shut it off it continued to chug several times before stopping. Then I opened the hood and there was wispy white smoke or steam coming out of the air cleaner. What would this indicate?

 

Good info on reading a vacuum gauge..http://www.secondchancegarage.com/public/186.cfm

 

sgbuick, Your choke butterfly stuck because the air cleaner wing nut has been overtightened and the center stud has pulled up and deformed the top housing of the carburetor, it will need to be replaced. Check your oil for gasoline: smell first then rub some oil off the stick firmly between your thumb and forefinger, if it chatters it is diluted from a failed fuel pump, if it feels smooth, compare to clean engine oil feel. To find your miss, crank it up cold and run for 20 seconds and kill it, feel of all the exhaust ports on the manifold for a cold one. Repeat another 20 seconds and feel again. Do this until it is too hot to touch and you should be able to identify your cold cylinder. After that you can concentrate on that cylinder or cylinders. This does take a little practice because of the manifold designs and thickness etc. As mentioned several times on this thread, a vacuum guage is a MUST HAVE tool. You should also get a spark tester, it is basicly a short spark plug wire that you can see the flash every time it fires. An inductive pickup timing light works even better as you can clip it on each wire while idling and watch the strobe for irregularities, a bad wire or fouled plug will not fire the strobe. After some initial troubleshooting you may need to get a compression tester as well to identify problem if ignition is not the issue.

 

Got the vac. guage today, will possibly have time tomorrow to try it out.

Texasjohn55, thank you for all of that useful information.

Can I just bent the top housing back into shape where the wingnut stud goes in? I never even thought that might be the cause of the choke plate getting stuck. If it takes several tries before it doesn't stall, should I check the manifolds for 20 seconds after it's continuously running?

I like the idea of the cold exhaust ports. Will this work on a standard log manifold (not headers)?

 

You can try driving the stud back down until it loosens the butterfly up, I did on mine but you run the risk of cracking the casting, no great loss because it needs replacing anyway. After you get the choke freed up, it should stay running. Feel of the exhaust after even 10 seconds if you like, just don't run too long at any one time so you can guage the temperatures by feel. It does work on log manifolds. After it gets too hot to touch you can use an infrared temp gun which you can by at Harbor Freight with laser spot for about $35.00, works very well on warm engine and cold as well. Just point and shoot. The inductive pickup timing light can be bought for $30.-$35. on sale, great for finding bad plug or wire, just clip it on and watch the strobe. Once you identify a cold cylinder, the battle is half over. Vacuum readings at idle will be useful also, especially if it pulses badly. John

 

OK, I got the vac. guage hooked up. Very interesting, though I did not see my reading on the chart in the link above. At idle in park, it is at about 22, fairly steady with some "needle shake"-type vibration. When it is in drive with the brake on, it fluctuates between 15-20 and when accelerating it fluctuates a little wider, maybe 12-20. Prob. expected since it shakes so much in Drive. Also, like I mentioned before, it gets worse in Drive the longer the car runs. Maybe a bit more fluctuation after about 10 min. of driving.

I managed to get the buttefrly plate to move, albeit somewhat creaky/squeeky, but it moves. And it doesn't stall anymore when cold. That is either bec. I plugged the 2 choke pulloff vacuum lines or bec. I moved the plate. Prob. means that I will have to move the plate manually when cold, since there is no fast idle mechanism on this carb. Also, I was able to kick down the idle, which I couldn't do before.

---------- Post added at 10:12 PM ---------- Previous post was at 10:09 PM ----------

Oh yeah, forgot to mention, in Park when I rev the engine, it went up to about 25, then slowly sinks back to about 20

 

I would start by setting the initial timing to 10 degrees and then the idle mixture screws to 2.5 full turns out from fully seated. From there I would fine tune the idle mixture screws and set the idle speed to 700 RPM when in gear.

Then if you still have fluctuating vacuum levels then look for a vacuum leak around the carb and intake.

If you can not find a vacuum leak then remove the valve covers and run the engine... ensure that all the pushrods are spinning slowly as the engine runs and listen for any tapping.

If you find a pushrod that does not spin or you have clatter in the valve rockers on the heads then you likely have a damaged camshaft and or worn/broken valve rockers.

if you still can not find a reason for a fluctuating vacuum then do a compression test on all 8 cylinders and then if you find one or more that is low then do a leakdown test to determine where the lost compression is going (leaking/broken piston rings, or valves not seating in the heads).

 

Replaced the broken brake check valve and hose, removed the PCV, and also capped off all vac. lines except the brakes and vac. advance (hooked up to ported vac. anyway), still same issue. Will try to check the plugs/wires and/or dist. cap next.

A couple of other things I noticed that may narrow it down - I'm getting a ton of fumes esp. when stopped in one place, when I'm done driving my shirt and everything that was in the car smells like exhaust fumes - Maybe the tapping sound I'm hearing might be an exh. manifold leak? Or does that mean it running too rich? BTW the fumes were there before I removed the PCV and I blocked off the hole with a rubber plug.

Also, when in park and idling I can hear an occasional kind of soft pop/misfire from the exhaust, mainly from the pass. side.

 

Sounds like one of two things:

1. An ignition miss.

2. Rich idle mixture setting on the carb.

I would use a timing light to ensure that all the plug wires are firing consistently... Use the light on each plug wire. Also run the engine in the dark and look for arcing.

Have you set the idle mixture screws yet? When you said it got worse the longer it idled it reminded me of a time I had too rich of a setting on the idle mixture screws and it was loading up and smelling really rich.

Bottom line is you are likely either not burning all the fuel due to a weak or damaged ignition system or you are too rich.....

Go back and re-read my last post where I describe other ways to determine your issue.

 

Sounds like carb needs to be rebuilt, the 2 barrel carbs weren't the best to begin with and if it's original it probably needs to be cleaned out and gone over . It's a pretty simple carb to rebuild ! But check the simple stuff first points,cap ,rotor ,plug wires for sure ,then move on from there.

 

Checked the cap and rotor, don't see anything unusual other than a tiny bit of carbon next to one of the terminals inside the cap. Also, several terminals had tiny black spots on them so I sanded them down, nothing major though.

Texasjohn55, I decided to do the exh. manifold heat thing by squirting water on them when hot. They all sizzled, but I did notice that the center of the driver's exh. manifold seemed to cool down faster than the rest, does that mean anything?

Also, when I removed the plug wires from the dist. cap I noticed that 2 wires had the terminals squished into the top of the elbow, rather than hanging down into the plug wire end. Will have to pull the metal terminal down into the wire end with a needlenose pliers.

 

I hope you put it back, dont delete the PCV from your engine.

 

Spraying water on the manifolds would work if you hosed them down good and started checking temps with an IR temp gun to compare the warm up speed of each on one bank at a time. Have you checked spark at each wire as suggested with an inline spark tester or with an inductive timing light? Have you checked that the oil isn't overfull or diluted with gasoline? We may be kind of stumbing around in the dark if we don't actually do some troubleshooting instead of piddling with cap and wires, that doesn't pin down a problem for sure, just vague possibilities. Does it fire the plug? That's what I'm trying to get at here. TJ55

EDIT: Wildly fluctuating vacuum readings in rapid repetitive pattern suggests a misfire condition, we are trying to ascertain from what cause. Wandering readings suggests a mixture problem such as idle adjustment.

 

Well, at least some positive - I changed the oil and used 1 qt. Marvel Mystery Oil and the lifter-type noise seems to have subsided, at least for now. That also elimintates the oil issue, though it didn't have any gas smell or grittiness before. Now just have to fix this rough idle.

Texasjohn55, the vacuum readings were more toward rhythmicly fluctuating w/ engine speed, even when accelerating. When I hit the gas at idle, it went up to about 25, then down and then slowly back up again.

 

Judging by what you said about the plug wires, and the vacuum readings you are likely having a missfire on one or more spark plugs. I would replace all the plugs, wires, cap and rotor and then set the initial timing and go from there. If you still have a poor idle then the carb would be the next thing I would tackle.

 

Ruh-roh - now getting surging/misfiring when accelerating as well, before it was only at idle

Will check plugs, timing, etc. on Monday. Already replaced plug wires, cap and rotor are Ok, adjusted mixture screws to max. vacuum but it needed over 4-5 turns to get there (??).

Also noticed something quite unusual - I decided to check the wires in the dark to see if any sparks flying, etc. Only noticed the porcelain part of the plugs with blue glow flashing around them, which I think is normal. But also noticed an occasional blue spark coming out of the exhaust manifold gasket area where it meets the head (??!!) I wonder what that means?

 

I would try setting the timing by ear, I had a similiar problem not as bad as yours though and even though the timing light said everything was fine it was way out . Apparently my dampner has twisted or slipped. Once set by ear it runs pretty good.