CaptainK
Administrator
All the time I've had my Corvette its had this issue that when the engine is cold, aka for 5 -10 minutes after engine startup, it would try to cut out if you went to pull away from a standstill, and didn't feel especially powerful until warmed up. I figured its was an old car, and fair enough as I'm not great until I've warmed up too. I don't drive it hard, so it didn't massively bother me and I just adapted to it. Once up to good temperature it seemed fine.
That said over the years I've had the car I've tried lots of different things including:
New carb, to eliminate any issues with the chinese copy of a Carter carb that came with the car.
New intake manifold.
New HEI distributor (though it had one before), complete with new plugs and leads.
New "headers" exhaust.
New PPV (?) valves from engine to carb.
Eliminating air leaks from vacuum hoses.
A whole tuning setup on a rolling road.
Probably other stuff I've tried and forgotten about.
Obviously all the usual service items etc too.
Each bit seemed to help, especially the new carb and having it tuned. That made the car much better when warmed up, but still had this cold issue, though not quite so bad. Like I said, it didn't bother me enough to really fix it, and most of the stuff listed above I did because I wanted to update the car and get rid of some of the old stuff on it. At no real point was I specifically trying to fix this issue I had, other than getting a new carb to replace the cheap chinese copy. Though over time, the issue seemed to get a little bit better and i didn't get as many "cut outs" when pulling away - or was I just better at managing it?
Anyway, its been ten years since I've owned the car now, and during this summer for some reason it started to smell a little bit petrolly when I was driving it. Not overly bothered again, old carb car etc. But looked into it and common solution is the petrol tank cap gasket has gone. Had a sniff around my cap, and yeah, it did smell a tiny bit. So I thought I may as well replace it. That's when I started looking into the part I needed to replace.
You see, my C3 is a 1968, so all bets are off when it comes to parts for a one year only model. In my research I found most replacements come with a new cap as well. Problem was, all the 1968 caps + gaskets I was finding didn't look like the cap that was on my car. The main difference being the outer shape of the cap, and the writing on it. The writing on mine said "Non-vented", whereas the 1968 caps I was finding said "Vented" on them. Did some research on why, and it turns out early C3 petrol tanks vent out of the petrol cap, whereas later ones use a charcoal canister in the engine bay and the petrol tank vents out through a tube to said charcoal cannister - the reason being is better for the environment that the fumes go through a charcoal cannister instead of direct to air. I can only assume that the previous owner of my car in the USA put a "non-vented" cap on because they are more plentiful and cheaper. Oh and for those like me that didn't know - venting is required to equalise the pressure in the petrol tank. Either from the fumes, or from replacing the petrol consumed with air, otherwise you form a vacuum in your tank and the fuel pump has to fight the vacuum which leads to the engine not getting enough fuel and could cut out / splutter / feel low powered etc.
Quick contact to EMC and a new correct 1968 vented cap is ordered in the hope it cures my slight petrol smell. It seems to be better now, so worth doing. It took me a few drives of the car before I realised that I wasn't having to "catch" the engine when I pulled away from a standstill when the engine was cold. It'd been second nature for me to do it for 10 years without realising, just the character of the car I'd adopted to. As soon as I realised that, I put the car in the garage and left it for a few weeks to go properly cold. Then started it up took it for a drive and paying full attention to my pull aways and deliberately pulling away a bit quicker from cold. Needless to say there was no issues, and car now pulls away fine when cold and seems more powerful when cold too. I can only assume that previously when my engine warmed up previously that something just opened up a bit to allow an air leak or something to allow the tank to vent, or was forced open by a warmed up engine, and thus engine ran better when warmed up. Gosh knows what, there aren't any leaks or anything anywhere that I've found. But right now the car is a different animal when cold.
TL;DR:
1968 C3 had cold driving issues, solved by changing a petrol tank cap from a wrong "Non-vented" one to the proper 1968 "Vented" one.
That said over the years I've had the car I've tried lots of different things including:
New carb, to eliminate any issues with the chinese copy of a Carter carb that came with the car.
New intake manifold.
New HEI distributor (though it had one before), complete with new plugs and leads.
New "headers" exhaust.
New PPV (?) valves from engine to carb.
Eliminating air leaks from vacuum hoses.
A whole tuning setup on a rolling road.
Probably other stuff I've tried and forgotten about.
Obviously all the usual service items etc too.
Each bit seemed to help, especially the new carb and having it tuned. That made the car much better when warmed up, but still had this cold issue, though not quite so bad. Like I said, it didn't bother me enough to really fix it, and most of the stuff listed above I did because I wanted to update the car and get rid of some of the old stuff on it. At no real point was I specifically trying to fix this issue I had, other than getting a new carb to replace the cheap chinese copy. Though over time, the issue seemed to get a little bit better and i didn't get as many "cut outs" when pulling away - or was I just better at managing it?
Anyway, its been ten years since I've owned the car now, and during this summer for some reason it started to smell a little bit petrolly when I was driving it. Not overly bothered again, old carb car etc. But looked into it and common solution is the petrol tank cap gasket has gone. Had a sniff around my cap, and yeah, it did smell a tiny bit. So I thought I may as well replace it. That's when I started looking into the part I needed to replace.
You see, my C3 is a 1968, so all bets are off when it comes to parts for a one year only model. In my research I found most replacements come with a new cap as well. Problem was, all the 1968 caps + gaskets I was finding didn't look like the cap that was on my car. The main difference being the outer shape of the cap, and the writing on it. The writing on mine said "Non-vented", whereas the 1968 caps I was finding said "Vented" on them. Did some research on why, and it turns out early C3 petrol tanks vent out of the petrol cap, whereas later ones use a charcoal canister in the engine bay and the petrol tank vents out through a tube to said charcoal cannister - the reason being is better for the environment that the fumes go through a charcoal cannister instead of direct to air. I can only assume that the previous owner of my car in the USA put a "non-vented" cap on because they are more plentiful and cheaper. Oh and for those like me that didn't know - venting is required to equalise the pressure in the petrol tank. Either from the fumes, or from replacing the petrol consumed with air, otherwise you form a vacuum in your tank and the fuel pump has to fight the vacuum which leads to the engine not getting enough fuel and could cut out / splutter / feel low powered etc.
Quick contact to EMC and a new correct 1968 vented cap is ordered in the hope it cures my slight petrol smell. It seems to be better now, so worth doing. It took me a few drives of the car before I realised that I wasn't having to "catch" the engine when I pulled away from a standstill when the engine was cold. It'd been second nature for me to do it for 10 years without realising, just the character of the car I'd adopted to. As soon as I realised that, I put the car in the garage and left it for a few weeks to go properly cold. Then started it up took it for a drive and paying full attention to my pull aways and deliberately pulling away a bit quicker from cold. Needless to say there was no issues, and car now pulls away fine when cold and seems more powerful when cold too. I can only assume that previously when my engine warmed up previously that something just opened up a bit to allow an air leak or something to allow the tank to vent, or was forced open by a warmed up engine, and thus engine ran better when warmed up. Gosh knows what, there aren't any leaks or anything anywhere that I've found. But right now the car is a different animal when cold.
TL;DR:
1968 C3 had cold driving issues, solved by changing a petrol tank cap from a wrong "Non-vented" one to the proper 1968 "Vented" one.