1980 with a 305, 650cfm Holley Carb

(note: the carb is too big for the engine, it's how I got it and I've yet to get a smaller one. The jets have been taken down 3 steps from default)

So the car has been running fine for a few months, no issues other than it running rich. About a week ago we noticed a vaccum leak and plugged it up, which lowered the idle speed and made the engine sound generally better.

The problem with this is that it ran less lean, so the exhaust was too thick and would choke me when I drove. So yesterday I took the plugs off the vacuum leaks (restoring it to how it was for 3 months).

It ran fine until tonight, when it stalled at a light. Now it won't idle for more than a few seconds before flooding and stalling. When the car is off, I can see fuel still dripping into the carb (circled in red on the pic).

Does anyone have any idea what is going on/what to do? I can't afford a new carb right now, so I'm looking to fix what's broke

red circle is where the fuel is dripping into the carb when it's off
blue circle was the vaccuum leak spot

 

sounds like you might have a float adjustment problem or a stuck float needle. You may need to disassemble and inspect. if you have never done this or not in a long while, make sure you have replacement bowl gaskets before disassembly. google how to adjust a holley float. Hopefully this will do it.

 

Sounds like a carb problem. Are floats adjusted properly? May want to get a rebuild kit for your carb and go through it. There are several things that would make a carb run rich.
(Oops, just noticed the previous post.)

 

Thats a major vacuum leak that you uncapped. You need to cap that again.
As mentioned before, you have a float or needle/seat problem. A piece of rubber fuel line will hang the needle open bad.
You can pull the needle and seat assembly out of the bowl without even removing the bowl to check for trash.
If you look at the top of the carb, that slotted screw with the hex head under it is your needle & seat assembly for that bowl. Just unscrew it and look to see if there is any debris in there. If there is its no problem to clean it out. If its clean, there is a good chance that your float no longer floats.
By the way, your car came with a 750 cfm carb. Why do you think a 650 is too big?

 

TY for the info, I'll be checking that out shortly.

I'm not a mechanic, I'm new to this car stuff. I bought the vette with the 305 in it (not sure if it's stock or not) and the 650cfm carb. I've been told that I should have about a 500cfm carb for a 305. All I have is what people tell me, everyone locally says 650cfm is too big.

 

Those that already know everything, ignore....

The needle and seat cuts off the flow of the fuel when it rises to its specified level in the fuel bowel, So.......before you take it apart if you have access to a air compressor, remove the fuel line from the carb and blow air into the carbs fuel inlet to remove any possible dirt or debris that could be holding the needle off its seat....Its worth a try and works more often than not....and with any type of carb...

is that ok PC Police

 

We pulled apart the carb and cleaned it out. It seems to be working correctly now. We also adjusted the float levels as suggested.

Afterwards, the engine was still flooding, but there wasn't fuel dripping out after being shut off.

I just adjusted the air/fuel idle screws (they were out 3 full turns, I set em to 2 full turns each) and increased the idle speed a bit. Now it idles without flooding (unless I need to wait longer than a couple minutes), but it sounds really rough, I'm guessing timing. I included a video, but the sound may not be good enough to really be useful.

Without a timing light, what am i listening for if I adjust the timing by ear? And which direction advances/?slows? the timing?

Also, vacuum leak is recapped.

TY for all the help

Video attempting to let you listen to engine idle:
http://www.youtube.com/watch?v=VtKRtrkEOXQ

EDIT:
Once it cools down I'm going to change out the spark plugs, also found an exhaust leak I'm going fix. Results tomorrow.

 

It came with a Q jet capable of 750 not actually a 750. Whereas the Holley actually is a 650.

 

Hard to tell by just looking @ your video but if I had a guess, it looks like your dist is set a bit on the advance side. Should take it to a mech that has the proper tools to check and reset if necessary. Are you getting black smoke from your exhaust while idling? If so, that could still be a rich mixture. You can try to dial in your screw down to 1 1/2 turns. You may need to re-jet as well.

 

Update:

I double checked the float levels, adjusted the idle air/fuel screws (put them at 2 turns out), changed the spark plugs (they were fouled), and fixed a major exhaust leak.

After all of this, the car ran great aside from the black exhaust from still running rich. At idle you can see it pretty decently, if I stepped on it I would get a pretty big black cloud. After about a day of driving, it is once again missing, probably fouled plugs again from being too rich.

I will be getting my hands on a timing light and pressure gauge tomorrow to adjust the dist and air/fuel idle screws properly. As mentioned before, it's a 650cfm carb on a 305 jetted down 3 steps from default. Do I need to jet down even further?

Running rich in this setup, what is the proper first step to fixing it?

 

You can turn your idle screw in more. I run mine @ 1 1/4 out and thats what works good for my motor. Try 1 1/2 and see if any improvements. Especially your prim.

 

I just did the test where you screw the idle screws all the way with it on to test the power valve, power valve is fine.

Pulled a couple spark plugs, they are indeed already fouled after just a day.

Question: When adjusting the idle air/fuel screws, which way is which as far as more/less fuel/air? Which way would I turn them to lean it out?

 

In to lean.

 

I replaced the power valve and cleaned the spark plugs, now there is a dead spot. The power valve I put in was 1psi lower than the old one, would this cause the dead spot?

Update: I put in a brand new power valve the same psi as the one I used when it ran well, no change. To describe what is happening fresh:
From a stop, accelerating seems 'bumpy', meaning the car kind of shakes until it gets going a bit. Once I'm going, the shaking calms down, but the engine is still very rough. If I step on the gas, sometimes I will hear a loud 'click', and it sounds like everything just stops (like a brief moment of silence) for a second then it kicks back in. Any ideas?

 

Get a 500 cfm for that 305 engine. Buy a Holley if you want to fiddle with the carbuetor and tune it to optimum performance. Buy an Edelbrock if you want to put it on, adjust a couple of screws and ride. Your choice.

 

Thats some twisted logic there.
That vacuum secondary Holley is a 2 barrel carb until engine demand opens the back 2 barrels.
When they are open it is capable of flowing 650 cfm. The Q-jet is capable of flowing 750.

Also, not that it matters much but that carb appears to actually be a 600, not a 650.

 

Try adjusting the idle A/F mixture using either the rpm method (highest rpm with 1st screw, then again with second screw, while retuning the idle to keep it at acceptable levels), or with a vacuum gauge- same thing but highest vac. The re-time it. Maybe a tune up is on order (Cap and Rotor)?

Will