Hello! I have a 77 Regal's 350 in my 77 Skylark with pistons from a 69 350 4bbl, with an iron intake and quadrajet from a 78 350. She usually runs great, and has proven very dependable over the past few years as she's been my daily driver. I keep running into an odd problem that seems to me like a vacuum leak. Usually starts out of nowhere, usually when coming off the highway but sometimes right when starting cold or anytime. Idle (normally kept at about 1000 RPM in neutral, 180 deg coolant temp) will drop to around 400-500 and it sputters erratically but won't actually ever stall out. The car drives just fine as long as you don't stop, WOT is great like always, but idle is terrible. I've rebuilt this carb twice so far, the second time with a good mechanic watching over my shoulder. Sometime this problem disappears for months only to rear its ugly head, and I'm about fed up. I've emptied cans of carb cleaner into the carb and around it and on all the vacuum lines with no effect. All the lines are new, and hooked up correctly, with the stock heated intake and EGR. The valve in the exhaust on the drivers side has been removed and the vacuum line blocked. I've tried dumping seafoam and iso-heet and a couple other things into my tank, but still there's no difference. Suddenly she will just start running fine after running like crap for a week, with no rhyme or reason. I've also checked the distributor just this morning, and both the centrifugal and vacuum advances are working properly according to my timing light. Do I need to just fork over for another carb, or is there something else I'm overlooking? I'll greatly appreciate any and all suggestions. Thanks, Noah Putman
How's the rest of the ignition system? Get the spec's on the ignition coil and ohm it. Even better if you can shut it down while it's acting up and pop it out to test it (and see if it's heating up). Other thing to look for is sparkplug wires. Watch the engine run at night and look for possibly arcing which would keep that plug(s) from firing. Also you say you have the EGR hooked up?? This can certainly cause intermitted issues if carboned up. If the valve is hanging up on a chunk of carbon it'll let exhaust gases into the intake at idle, effectively causing the same symptoms you're seeing.
EGR valve is new, from AutoZone a year ago ($$$$$!). I tried pushing the diaphragm up and down a couple times while running it this morning. It started stumbling worse when I pushed it but didn't solve the problem when I let go. I think I'll take it off and see if there's something going on under there. The ignition system should be decent, cap, rotor, coil, module, wires, plugs are all about a year old and I couldn't see any arcing. However, the inside of the cap's terminals are all white and I can hear a sort of slight buzzing sound from it. The rotor isn't burnt underneath or anything so I don't think there's a serious issue. It's always done this and after replacing everything it never went away so I forgot about it. ^.^ I'll take a look tonight and see if I can spot any arcing. That buzzing sound is suspicious though but I don't know what to do about it and as far as I can tell it doesn't cause any huge trouble.
I'd clean the bottom of the EGR valve with some brake or carb cleaner, then install it and leave the vacuum hose unhooked (plug the hose). At least remove it as a potential source of trouble until the problem is solved.
I pulled the EGR valve and cleaned it. It was definitely blacker then when I put it on new but it wasn't very bad. I sprayed it with PB Blast and wiped it out with a rag until the little bit of carbon was gone. EGR back in place, line plugged, no different. Also, I forgot to mention that closing the choke smooths her right out and brings the idle up. Is there anything else I could possibly be forgetting? My Ts are tight and the tranny modulator line isn't leaking. It's usually something small and obvious with my luck. Thanks!
When you say 1000 rpm idle in neutral, and 450 rpm idle in gear that seems to me like a vacuum leak somewhere.
Either vacuum leak or your idle circuit in the carb is gunked up. Pull the carb apart, hose all of the orifices with carb cleaner, blow it out with compressed air, and reassemble.
What I mean by the idle speeds is that when she decides to run right it's 1000 in neutral, and when she's being ornery (today) it's 450-550 in neutral. That'll be the third time doing that to this carb. Maybe I should take it to someone a little more experienced than myself this time. I guess there's not much else it could be, huh? o No:
If the idle goes Up when you close choke its letting air in some where else. vacuum leak. plug every vacuum hose even pcv and pull the oil fill cap and see if you have vacuum there.
The engine is not stock. After changing the cam I had to bump the idle to keep it friendly at stop lights when in gear. I probably could get away with it being a little lower but I'm more concerned with having it idle at all at the moment.
By blocking the air supply with the choke is like adding more fuel. So my thought is the carb. is running lean for some reason. What many do in an instance such as this is to go larger on the jet size or install a smaller O.D. metering rod. This adds the fuel nec. but is a stop gape method. It solves the symptom, but hasn't solved the REAL problem. Just my thoughts. Tom T.
Has the 78 Q-jet been calibrated for your engine, or is it stock. If it is stock, you can't expect it to run right. Also, why run EGR at all?
I would check the voltage from the coil and see that is changing when the car runs rough vs. smooth. Also if you have a timing light then check each plug wire for a stable idle. Could also be a chunk of something from the fuel tank that will not dissolve in the carb cleaner. Have you tried a bottle of fuel injector cleaner in the fuel tank? Spraying carb cleaner at the carb will not help in inside much if any. If you end up still thinking it is the carb then you can get one from ken that is fully rebuilt and he can even customize the fuel metering for your combo. http://www.everyday-performance.com...:category=578011&mode=product&product=6010109
Yup. Jets 'n' rods don't change idle mixture. There's a batch of changes that can be made to the idle circuit, though. (air bleed size, idle tube restriction size, idle down-channel restriction size, size of holes the idle mixture screw tapers go through, etc.) Yeah. Be careful with the EGR, though. Lack of EGR on an engine tuned for EGR can make for terrible ping. Will need to recalibrate the ignition advance AND the fuel curve to fix the ping. If the cam in question is the 252H in your signature, and if the carb is working right, you should have no idle problems. That cam is ultra-mild. NO need to increase idle speed. WHAT is your cranking compression? Was the cam degreed when installed? I see this problem as two-stage: The engine doesn't idle properly at best, and that needs some correction. Second stage is when the engine runs worse than usual, a problem that comes 'n' goes. I'm not sure that fixing the first will also fix the second--but it's worth a shot. How 'bout the calibrated air leak from the PCV valve--is the valve good? Not varnished up? PCV hose isn't rotted?
I have the idle mixture screws out a couple turns more than what I'd read other places, but when she is running well the idle is usually fine. I've also tweaked the air valve spring (I think that's its name? controls the flaps on top over secondaries) a little to remove some bog when putting it straight to the floor. I got the carb and manifold from a junkyard and never saw it run. I rebuilt it first thing and it seemed ok. Eventually this problem started and I tore it down and rebuilt it again, only to hide the problem for a little while longer. It's came and gone several times since then. I almost wonder if I'm using a poor quality carb kit or something. The reason for the 252H cam in question is that this is my daily driver not a weekend warrior, and the old cam lost a few lobes due to a stupid oiling problem caused by a lazy machine shop's cam bearing slip-up. The cam was installed straight-up about 10,000 miles ago. I am definitely aware of the need to retune everything to run without EGR, and this is the reason I have been running it. I always run 93 octane and have played with distributor weights and springs and an adjustable vacuum advance to get everything tuned as tightly as I can. I have no idea what my cranking compression is off hand, as I don't own a compression tester. I could borrow one and check it but I really hope that I don't have problems here... PCV valve and grommet are good and clean, hose is also good. Both have been replaced within the past couple years. Blocking the PCV hose makes no difference. I've been chasing this bug around for quite a while now. I just got the car inspected last month with complements from the mechanic, and for the past 2 or 3 months everything's been good, until yesterday. I really don't want to have to replace the carb but I'm starting to feel like I'm beating a dead horse here.
Take some time to confirm the simple things like voltage from the coil... Spark consistent at each plug wire? Check the timing at idle to make sure that it is the same when it is idling strange vs idling normal. I find it best to tune the idle mixture screws to get max vacuum with the wheels blocked and in gear. All you need is a vacuum gauge and a screwdriver. If you find that one of your idle mixture screws is not effecting the idle then remove the screw and spray some carb cleaner in there and then rev the engine and cover the carb with your hand... This usually frees any debris in the idle passage... They do clog up sometimes.
