First off, I'd like to say hello. Been reading these forums for a long time and I finally decided to join. About a week ago I purchased my first C3, something I've been wanting for a very long time. I've had 3 C4s, but they just aren't for me. Well anyway, here's the story. I found my '77 with a great body and interior, with only a few minor flaws as any 38 year old car would have. It is a L48 which really didnt matter to me since I have a 454 that I plan to put in one day. After getting it home and inspecting it more than a short walk around and test drive, I give it some maintenance that is expected on any newly purchased car (oil, filters, etc.) After changing the tar black oil and filling it up, half of it leaked down the block from a bad valve cover gasket. So upon changing those I find that I have roller rockers. Next, the engine wouldn't get to temp and find low coolant and leaking pitted thermo housing with broken ported vacuum switch. Fixed that and now I have cold start choke. I bought the recommended air filter and it wouldnt fit. Come to find out the air cleaner lid was changed. I'm guessing because they changed the intake to an Edelbrock Performer(3701) and the carb to a Holley 4175.
Now to the problem.....It seems that the carb keeps flooding. It'll start fine when it's cold.When driving it'll drag *** when it takes off. Higher RPMs it seems fine with plenty of power. I went to lunch today and after I ate, it didn't want to start. Did the same thing this evening. I went to get some beer, started up, backed out and died. Cranked it forever and finally started.
I'm not the most educated when it comes to carburetors. Ive been researching how to adjust this one, but you cant change the float without taking it apart. That leaves the idle screws, but it idles fine. After I got home, I took off the air cleaner and I could hear the carb hissing(with the engine off) for a good 5 minutes....and the throttle shaft was wet. Like I said, carbs are kinda new to me, so I was looking for any advice or tips and tricks. Is my only option just to buy a rebuild kit and go thru everything?

 

I am guessing that you may have a couple of problems. The hissing - are you hearing vacuum leaking down from one of the connections to the intake or carb?
The flooding after running and shut down for a while - could be fuel percolation/boiling. Winter blend fuel boils at a lower temp. But, is it really getting that hot in a heat soak?
The fuel on the throttle shaft - I am guessing it is the rear shaft. Could be rear float or needle/seat problems, or the percolation.
What would I do? Rebuild kit. If it has been sitting for a while or just several years old it probably needs a re-fresh.

 

Thanks for the response. I'm not exactly sure where the hissing is coming from. It's down inside the carb, and it's louder, or I can hear it better when I open the butterfly valves. I didn't think it got hot enough to make a difference, but since you mentioned the heat soak, as I said before, Bubba changed the air cleaner lid, and the stock size filter doesn't fit. So I bought the closest one they had, but it leaves about a 1/4 inch gap between the air cleaner base and lid. Would that affect it?

 

Heat soak would be the engine getting hotter because it was turned off and the coolant no longer circulates. The temp can then rise higher than normal and the carb/fuel gets too hot and boils. It is not an uncommon problem. Having it happen in January might be uncommon. They make heat shields and carb spacers to help with heat soak.
Your "hissing" doesn't sound like a carb issue to me, it could even be compression leaking back. The air cleaner lid would not hurt any of this.

 

Im in Texas and it was close to 70 yesterday, so it wasnt too cold out. I even had the T-tops off. Compression leak would mean the intake valves, right? I just ordered the carb rebuild kit so I'll just try to tackle one at a time.

 

Did they keep the fuel return line when they switched to the Holley?? That would help the hot start issues.

Ask Lars here from his White papers on ignition and tuning. I would also plan on getting the carb rebuilt and dialed in. If it sat for a long time it may be pretty bad in there.

 

See this thread for a return line.

https://www.corvetteforum.com/forums...turn-line.html

 

Yea, Its pretty warm here as well. You can still get hot in the winter, it just depends on how hot your car is operating. But I would bet a carb kit will fix you up. Not trying to tell you what to do, but I always use a vacuum gauge to tune my carbs. An intake valve could be hissing a bit. Since you hear the noise below the butterfly, it is probably coming from the intake manifold.

 

Ddawson, thanks for the post. No, it doesn't have a fuel return. I read the links, and that's some good info. It has two lines going to the fuel pump and one line from the fuel pump to the carb (with an inline filter). This carb only has one fuel inlet. So, should i obviously need to correct this, but where does the return line go? To one to the lines attached to the fuel pump?

74modified, I just put in a 195 Failsafe thermostat, and the temp stays right there. I dont have a vacuum gauge, but Im all for buying new tools, lol. If i take the carb off to rebuild , I'd do the intake gaskets too because I'm curious to see if they changed the lifters as well. Another thing, I read to check if the throttle shaft is loose. It wont move in and out, but it moves slightly up and down. Should that be a concern, because I know that is more than a basic rebuild. Oh, and here's a pic if it matters.

 

The small line (5/16") coming off of the pump is the stock return line. The idea is the bled off fuel returns to the tank so it doesn't sit in the line and gain heat. In a perfect world the bleed or regulator would be up by the carb (like Lars uses) so cool fuel would always be available to the carb.
Here is the kicker, pump gas can boil/vaporize at less than 200deg F - it depends on the mix. If you have an exhaust crossover in the intake, or some other factors, the carb can reach some pretty high temps. I still think you just need to re-fresh the carb, and wouldn't start changing multiple things.
If the throttle shaft bore is worn it can cause problems. But - not the problem you are experiencing. You said it runs great except for after shutting down? You could put bushings in or replace the throttle plate, or the whole carb. Maybe you should find someone who is experienced to take a look.

 

Remove that rubber hacked together fuel line ASAP. Too much risk for fire.

 

Will do ddawson. Well, I took a nice drive around town today looking for a decent mechanic. Most didn't even mess with carbs. I finally found one and he seemed pretty knowledgeable. He could tell instantly it was flooding. He checked the throttle shaft and said it wasnt bad. I told him I bought the kit and itll be in Monday. He said he'd help me rebuild it and tune it next week. If I were to make a fuel return at the carb would I need a new fuel pump or could I just splice into the fuel return coming from the pump? Thanks again for all the help, and sorry if I'm asking stupid questions.

 

You are not asking stupid questions - you are more likely to get stupid answers here. If you were to put a regulator or a bleed orifice return up at the carb, you would run it back down to the original return line and block off the existing return coming out of the pump.

 

So Bubba was at it again. My rebuild kit should be in tomorrow so i figured Id take off the carb today to work on it if i was lucky enough for it to come in early. Done. While I was at it I was thinking of taking off the intake and putting new gaskets, because what the hell, lol. I also wanted to take a look at the lifters since there's roller rockers. Haven't gotten it off yet, but I pushed down on each of the pushrods with a big srewdriver (with quite a bit of force). None of them budged, so this "most likely" means solid lift, right? Went and picked up a Go-NoGo feeler gauge set, all except cylinder 1&2 dont even have .004" clearance. (2 has about .024 and 1 has about .016) Also, the rockers dont have the allen wrench poly locks, just regular nuts. So my biggest concern is that if they werent adjusted and overtightened, that would leave the valves open and eventually burn them. Is there anyway that I can tell without taking off the heads and dropping them off at the machine shop?