As this is my daily driver, I need help ASAP please.

The car has been running great since the motor was dropped in last fall. noticed it did progressively seem to grow a slight hesitation, but nothing serious. Today, on the way to work, she died sitting at a light. I thought it was out of gas (no gas gauge and it seemed plausible with the mileage since the last fill-up). Fortunately, I was next to a gas station. I filled her up and was able to get it started. Fired up fine and idled ok until I started to pull out...she did NOT want to idle. I had to keep the RPMs up to keep it running.

And thats where I'm at. Starts ok and will even idle up OK, but after a minute, the idle starts to flutter, then drop, then die. It'll stay running if I keep feathering the throttle.

I pulled the PCV out of the valve cover and pulled it off and will the huge increase of air into the carb, the idle shot up and stayed there. Could it be getting too much fuel (since adding air seemed to help)? Stuck float maybe or something along those lines?

I'm waiting for it to cool down so I can do something, but wanted to try to get some ideas before starting

Thanks all!

Fuel filter? I had a clogged filter that acted just like that.

worth checking, but my fuel pressure gauge shows a nice steady 7.5lbs even when she starts sputtering. Wouldnt it drop off?

Car info? I assume this is on your carb'd chevelle?

Get a can of carb cleaner, pour some into the float vents to clear out the carb.
Vacuum advance hooked up?

sorry..forgot I took the specs out of my signature...

SBC, 350, .30 over, 10.5:1 pistons, Holley 4V 650 mech secondaries, elec fuel pump, turbo 400

motor has onle a couple thousand since the rebuild. Carb was overhauled at the same time.

if it matters, we got a lot of rain last night and the car was out...usually stored inside.

I'll try the carb cleaner now

i soaked the carb with cleaner...reved it way up to bump the secondaries open and sprayed it liberally down the throat. May have done the trick. I was able to put the PCV back on and its idling OK for now. I'm going to let it sit and try again shortly.

THe carb I'm using is fairly old, but was overhauled. It's a 650 that was, so I was told, professionaly flowed to 690. I've never be too thrilled with it for whatever reason.

In looking at carbs at Holley's website, they have a CFM calculator that asks a series of questions to see what would be best. Entering my info and chosing a vac secondary model, it suggests a 750CFM carb.

If I were going to buy a new carb, does anyone have a suggestion? Mech vs Vac secondaries...CFM...

as far as a new carb is concerned we need more info auto/manual, rear gears, cam size etc. I have a holley 850 doubble pumper on my 462 pontiac and only get 8mpg however the throttle response is great and with the mechanical secondaries the power comes on so fast I can break the tires loose at 40mph in either 2nd or 3rd gear. However for a daily driver concerned with gas milage you are probrally better off with a vaccum secondary such as the street avenger

gas mileage..schmileage. lol. I want RESPONSE

turbo 400 auto trans with a ~3000 stall. 3.55 gears. I don't have exact cam specs (billet hyrdaulic roller). I get about 10-12mpg now.

Sounds like a blown power valve or a clogged idle air bleed to me. I'm going to lean towards the power valve, since creating a huge vacuum leak with the pcv valve off helped it out a lot. A clogged idle air bleed will cause a hard to idle condition, but it's not giving fuel that's the problem, yours sounds like way too much all of a sudden.

I had this happen to me this weekend on a motor I just swapped in...it was the Vacume line open, I clogged it, and It has run every since!!

i was leaning toward blown PV as well. There isn't one in the rear bowl, so I may just pull the front bowl and plate and check/change it.

also is there any chance that the choke is staying on?

chokless

I have found sometimes if the bowl screws get loose fuel can leak internally around the metering block gasket causing an overally rich condition. Obstructed air bleeds can cause this as well and are very easy to clean with a shot of carb cleaner

Black, When the car acts up does it get rich,

ok, so the problem persists. Idles fine for a bit, then starts to stumble and wants to die...then it clears up for a bit...then bad again. I changed the fuel filter tonight and got a little better fuel pressure at the gauge. I pulled the carb, ripped it apart, cleaned and used compressor to blow everything out and dry, reassembled. Uhoh...TWO of the main bowl screws are stripped or stripping out! Interesting that a couple of replies ago, it was suggested that these screws could be the culprit! Lovely. Looks like I have a good reason to buy a new carb now...anyway, it idles fine tonight after this work, but we'll see tomorrow. Now a new post on carb selection...

thanks all!

I have had cracked rubber fuel lines suck air instead of leak fuel... and or soft rubber lines sqeaze together cutting off some fuel supply before also... that caused a simular problem as you are having.
Check all rubber fuel lines carefully before spending big $s

Other than a couple of short connectors between the fuel filter and tank and pump, I've got hard alluminum lines.

It idled pretty well this morning. I think I fixed the immediate problem, but with the bowl screw issues, etc...this carb is out.

Thanks again to everyone...now go to the next thread and help me pick a carb! lol