just bought a 76' corvette. I have above average mechanical knowledge but relatively unfamiliar thus far with vehicles.
The issue: can start OK and run while in neutral and applying gas, once gas is disengaged, idle drops below 500rpm and it stalls.
The choke appears to be stuck? open. Is this likely to affect startup/idle in normal warm weather. conditions? (assume roughly 70 garage temp)
Could adjusting the idle (fast or warm) be the solution?
TL;DR: help me fuck with my carburetor.
take this to / o / bud theyll take care of you
honestly it's worth paying someone to tune that shit once so you can find out what it should be like and what your other problems are.
>>947183
also, when I try to manually depress the choke, it 'catches'. sorry no pic of carb, my wife is due home any minute and she's already pissed I bought a sports car. <@:-)
>>947183
>TL;DR: help me fuck with my carburetor.
only if you promise to paint it like the mach 5
>>947186
good call, didn't mean to pollute /diy/ I rarely venture outside /b/... it's a fucking disease
>>947188
I'll happily have it tuned, but first I'd just like the fucker to idle without crapping out
>>947217
~$11k with shipping. 57k miles. one previous owner since '84. it's in decent condition but from what I was told just sat a lot.
>>947190
k?
>>947183
>unfamiliar with vehicle repair
>bought an ancient shitter
holy fuck anon, you are in for a wild ride. now go tell your wife how you're going to need to sink at least triple what you paid for it into repairs.
basically what is happenning is that at idle, the throttle body is closed. the engine now needs to run on almost no fuel and air just to keep it turning. when it runs at high revs, its dumping loads of fuel and air into the engine to keep it running the higher revs means one blown piston or one set of fucked valves or one spark plug is now masked by the other combustion chambers functioning.
an idle problem can be caused by a number of things. the usual cause is poor ignition or poor compression. in order of what i'd check
>spark plugs
>spark leads and terminals
>ignition coil
>what does the coolant look like?
>what does the oil look like?
>clean carby/check nozzles
>what does the exhaust look like when running?
>fuel pressure
>fuel pump
hopefully it's just an ignition or stochiometry problem like a valve isnt sealing properly. otherwise it will be a fun hunt.
https://www.gmheritagecenter.com/docs/gm-heritage-archive/vehicle-information-kits/Corvette/1976-Chevrolet-Corvette.pdf
>>947220
>it's in decent condition
who told you this?
>it just sat in a lot
that's what they all say.
>I was such a good owner I barely even drove it , it never saw rain and i waxed it every night while wanking myself to sleep
it's a sports car so I wouldnt be surprised if one day he decided to thrash it and bent a valve.
oh could also be a timing problem.
>>947226
>I'll tell the wife
I appreciate the feedback, seriously. Mainly something to fuck around with in my free time. hopefully nothing major, but if it takes awhile to make this 40y/o bitch 'reliable' no big deal. exhaust is clean, I'll start with the plugs and go from there
>>947232
no I mean white, black or blue exhaust smoke?
an idle problem indicates either unburnt fuel or not enough fuel. unburnt fuel will cause black clouds. water will cause white steam, oil burns blue.
if there is no smoke then it is running very lean ie. not anywhere near enough fuel. possibly fuel pump. possibly something as simple as a fuel filter change.
>>947229
understood. I could have easily paid $5k more and been left in the same position. if it's a project, oh well; just want to check try most obvious solutions first.
>>947234
yes, VERY minimal white exhaust at startup then clear. fuel filter could be the culprit, good starting point along with the plugs. thank you.
>>947239
on an engine that has been sitting white is fairly normal. because condensation causes the sump to fill with water over time. most cars will blow white smoke even after a day while warming up.
I had to idle my car when I bought it and rebuilt the head after a blown head gasket and oil change for 20 minutes before all the water cleared out.
OP, don't let these bastards get you down. I can never figure out why people shit on legitimate DIY on a DIY board. You're no expert on working on cars? Well, you're here to learn after all.
I'd go with some of the previously made suggestions. Could be an ignition issue (plugs, maybe the distributor is shot) or not enough fuel (carb problem).
>>947239
I've never worked on a carb'd engine before, just injected so i dont know anything about carbies other than to dump a cup of fuel into them while they're running to clean them.
but they deliver fuel through these things called jets. they get clogged and dirty. I clean these sorts of things using PVC priming fluid. it's methyl ethyl ketone mixed with some acetone. MEK is one fucking hell of a cleaning product(aircraft stripper, gasket stripper is another name for it). it will bubble off paint instantly so be careful. also, dont breathe this.
>>947257
also the pins tend to have a tendency to fall out when you disassemble them. so be careful opening it up.
Okay, it sat. Did it have gas in it? Are you potentially trying run gas that could be a year or so old? Gas breaks down overtime, you may be able to use a fuel stabilizer but you might have to drain it. Check the distributor cap. Mark it first so you put it back in the same position. Does it look clean? They wear out between 30,000 and 100,000 miles(as always, great design and quality control from gm) and will cause major issues with spark delivery when they wear out. If it's worn out you want to replace the cap and rotor, then adjust the timing(more on that later). Check the vacuum hoses. Are they dry rotted? Bad vacuum leak could cause a rough idle, but likely not a stall, but I've seen it before. PCV valve. It's probably on the drivers side valve cover and has a line running to the bottom of the carb. Take it out, if it rattles it's probably good, they like to get gunked up and stuck. If you feel comfortable with it check the spark plugs, make sure they're not covered in oil or corroded. I'm talking at the electrode, which means you'll need to take them out to see. They love to rust and seize on these engines, so be very careful. Make sure the spark plug wires are in good condition. A good way to check is to run the car with the hood up in complete darkness, if you see light coming from them they're bad. You can also do the red neck method, simply grab the wire while it's running and if you get an ouchie then they need replacement. It's more of a long shot, but they can go bad and have a severe jump in impedance that hampers the spark delivery. If all that checks out, go buy a cheap timing light and learn how to use it on YouTube. Look up your specific engine and year to learn what the timing should be. I'm guessing because it's a gm from that year it's around 25-35 before TDC.
>>947263
If so, make sure you get an adjustable timing light. Also, I don't think it was until gm started doing their TBI but there are certain years where you need to jump a wire, otherwise the computer will adjust the timing while you try to adjust it. Read up, plenty of info online. Ignition timing(not to be confused with valve timing) is what determines when the spark plug fires. Top dead center is when the piston has reached the end of a compression/exhaust stroke, as far upwards as possible. These engine need the spark to fire before the piston reaches TDC, I believe at 35°, to perform optimally. Could just be the carb is out of adjustment, but in the 80s at some point Chevy moved to non adjustable carbs on their small blocks, again I believe it was when they switched to TBI.
More abstract thoughts.
Fuel filter(unlikely)
Alternator is weak(unlikely)
Spark plugs were changed and wires weren't ordered correctly(unlikely in this case but pretty common, get a spark plug wire diagram for your engine just to double check)
Carb gasket is dry rotted(I would imagine this would cause high idle and bad/worse fuel economy, but anything is possible with these old bastards)
The issue you're having seems to be either not enough air or fuel, or a weak spark.
I would hazard to guess it's an ignition issue, so I would go through that system first. And ignition doesn't mean starting the car, it means the ignition coil, to the rotor mounted on the distributor, to the distributor cap, to the plug wires, to the plugs. At least on these cars.
>>947265
Next I'd check the vacuum system. There's a very unsafe way to check a lot of houses quickly. Starter fluid. If you spray starter fluid on a hose that's dry rotted with a lot on small cracks the car will idle higher. What's unsafe about this you may ask? Starter fluid is flammable. It's possible that there is some point on the engine that can get hot enough to cause auto ignition. That however is unlikely. What is more likely? Remember how I told you that you can get shocked by bad spark plug wires? They can also be an ignition source for flammable vapors. I've did the starter fluid method more times than I'd care to count or admit and have never had an issue, but the first rule of safety is avoid complacency. Just because it has never happened to me doesn't mean it never will.
After that I'd check fuel delivery.
I know you said the "choke" appears to be open. That's a butterfly valve, they're angled normally on these carbs. If it was truly open your car would be at 6000 rpms idling. These carbs are usually pretty solid, and even if they're in bad shape they'll still let the car run. Try going through it with some carb cleaner. If there are electronic fuel injectors in there DO NOT USE CARB CLEANER. It can damage them, this is the Throttle Body Injection system I mentioned before. Google how to clean it. You'll get a dozen different opinions, all of them wrong, but because it's a Chevy they'll all work. If that doesn't make sense, wait til you're 10 repairs into this car, it will.
But yeah, I'd
Replace old gas
Buy a Chilton or Haynes manual
Check the ignition system
Check the vacuum system
Check the fuel delivery system
Clean the carb
That's all routine maintenance anyways for these old bastards. I'll try to monitor this thread if you have more questions. I drove 80s Chevys for over a decade, had a suburban for 9 years. It's what I learned to wrench on, because I couldn't afford gas and repairs. I'm getting a late 70s blazer in the summer.
It might be wise to change plugs, plug wires, distributor rotor and cap. It's the first thing I do when I buy a new used car.
>>947183
>>947183
also check and replace vacuum hoses and air intake hoses.
engines generate vacuum when running. because the engine is sucking in air. older cars use this as a mechanical signal to open valves and for idle control. a vacuum leak causes fresh air to enter the engine, bypassing the carby. so basically making the engine run lean.
even if you can't see a crack, it can still be leaking. an old trick is to get a propane torch, not ignited and aim it at the hoses and joints. if the idle changes in a certain point then you know that it is sucking in the butane at that point. so instead of just fresh air, it's sucking in extra fuel which should raise revs.
>>947183
please post pics of the engine OP. also, pictures of hoses, under the air filter, it will give us an idea of which parts have and have not been serviced. leave dirty and grease on engine parts you havnt serviced. it's good for telling what has and has not been touched in a while. for instance, a dirty fuel filter with the paint flaking off it means that filter was never serviced. when I bought my daewoo it still had the factory OEM fuel filter at 170k km
>>947272
I'll post more pics tomorrow morning. I appreciate all the advice, and I understand to take it with a grain of salt. All opinions are helpful, thanks.
>>947186
>OP goes to /o/
>op comes back months later.
>help diy my engine died in my 76 corvette because I put 53psi of boost on stock internals because /o/ told me too!
>pic sorta related; but on a 76 corvette
>>947188
>my wife is due home any minute and she's already pissed I bought a sports car.
You fucking mangina, you deserve your incoming alimony.
>>947183
If the engine needs to have the pedal held while cold but doesnt while its warm you have a vacuum leak
OP, have you checked the idle set screw? Seems to be the horse to your problem. It's easy to get caught up chasing zebras instead. Before you even think about the zebras, change all your fluids, spark plugs, fuel filter, check vacuum hoses, tranny and diff fluid, shuft turret oil(I assume that since you bought a smog Era vette like a maximum boomer, you at least picked up a manual)
>>947383
Actually, it probably doesn't have enough power to run accessories at idle. Smog Era vettes had like 170 hp in gms dreams, probably slower than a miata by now.
>>947385
they do weigh about 3x as much.
gotta love that thick solid steel frame.
crumple zones? no, the car will outlast you. in the event of a crash you become a pink paste while the car bounces away unscathed.
if all else fails scrape the corrosion off your distributor cap
>>947390
>the car will outlast you
The frames rust at a weak point just in front of the rear wheels. Even when the rest of the frame looks okay, that area can be rusted through. Some C3 owners have literally had their car's frame buckle without warning while driving.
Not OP, but I saved a thread from you from a long time ago. Glad to see you made progress
If Op ever comes back, I can give him a hand. I have plenty of experience with old carbd v8s.
>>947486
the manual link I posted above does say that you need to service those points as a part of the schedule.
>>947486
>without any warning.
You mean to people who have no idea what they are looking at?
If the frame looked like that, that has been warning people for years.
>>947183
>76 Corvette
>not 68' Corvette
Enjoy not having sleek chrome bumpers and desperately explaining to everyone "I didn't want them anyway, I swear"
>>947193
Dont listen to him, /o/ is a fucking awful board that isnt going to help you do shit.
The shade tree fags here on /diy/ know more than the self proclaimed car nuts over there
>>947585
Anyone buying a 76 corvette knows exactly what they are getting.
Especially since they cost less than a C4 with injection problems.
>>947590
Chrome bumpers
>>947593
Chrome bumpers are the least of your worries when you are buying a post 1973 corvette.
>>947590
>Anyone buying a 76 corvette knows exactly what they are getting.
OP paid eleven thousand dollars for it.
>>947594
You mean like how the engine has its balls cut off because muh enviornment?
Or just the 3rd world assembly job?
OP knows there are MANY Chevrolet and Corvette forums so WTF is he/she/it doing here when they have extremely detailed info on every aspect of his Vette down to part numbers and paint codes?
Please, OP, avail thyself of the internet and post pic of carb setup ON VETTE FORUMS. since many things are often changed by previous owners.
I'd expect to drain fuel tank, rebuild carb or if crusty just buy a new one. I gave away piles of old Holley and Q-Jet parts to my bros because nice new carb prices nowadays make it not worth fucking with though I've overhauled many.
Chevys are ideal for learning, but /diy/ is fucking NOT the place to learn to wrench them. At least OP asked here and found that out.
There is much info on basic troubleshooting on these engines but IT DOESN'T FIT IN ONE THREAD.
Enjoy your Vette. It's a good way to learn and have large fun.
Take it to Los Santos Customs.
>>947257
well now is your time to learn. get yourself a vacuum gauge and a book on quadrajets [unless someone put a holley on it]
>>947183
remove the choke
>>947220
11 grand for a non running vette? Fuck.
>>947733
But its not just a vette, it is one of the weakest, cheapest, least desirable vettes of all time. You can find them for 2-3 thousands dollars.
Literally a Porsche 944 tier car.
>>947186
/o/ here, an ls swap is actually reasonable in this situation
>>947733
OP really jebbed himself on this one.
>>947576
It happened to a Boomer neighbor of mine... The exterior looked okay because fiberglass, he really didn't know how bad his car was.
That brings up the other problem with the C3 (and C4)... Boomers. They're mostly owned by geriatrics. I'd be embarrassed to own one because everyone assumes you're 50+, and all sorts of 50+ guys will start talking to you.
