69cvette

alright my dad just had the 355 rebuilt in his car, due to the rings never seating when the engine was built the first time. well after it was built, the edelbrock carb that was on it, was leaking fuel out of the back, so he bought a nice new holley carb and had it isntalled by the mechanic (the mechanic recommended it and all.) now it runs great, cold, but when it heats up it just loads up with fuel. so much that when he stomps on the gas nothing but a big cloud of black comes out of the exhaust, and when he starts it up after sitting for even up to just over an hour it'll start up but then, die out on him, because the car just floods itself right away, then he has to floor the pedal to clear the cylinders and start it up, all the while more fuel dumps out once it starts.

also when he went to start it on a cold start pumps the gas once to set the choke and it fires up on high idle but dumps out black smoke for like the first 30 seconds.

I told the mechanic who tuned the carb and all whats been going on, he said he can take a look at it, but really hasn't found anything wrong with how its tuned, or isn't sure what he will be able to find, as it doesn't make sense to him why its loading up so much with fuel.

please help me out here, I'm tired of watching my dad have to embarrassingly re-start his vette after it dies on him all the time.

the cars is a 4 speed 350/350. i always try to tell my dad to just run the car more than he does he drive it very lightly, sometimes I feel like its just how he drives it haha

scottyp99

The part about it running well when cold, but really rich when warmed up, makes me suspect the choke, make sure it is opening correctly.


Keep the shiny side up!
Scott

69cvette

the car idles nice and choppy at regular idle when you jab the gas it'll go right off choke, same if you do it again, it'll go right back on choke. i asked him if he was tapping the gas when he starts it up hot he said no.

Billysvette

Adjust the choke open all the time and make sure it doesnt close when driving,to see if this is your problem.Besides its summer almost ,you dont need it.I think its the choke.Loosen the outter screws on the choke housing and turn all the way to open and stay open,then tighten down the screws.

chadronvette

Could be a sunken float. Had that happen with a new Edelbrock. Remove both floats and check that one isn't full of gas. Also, if you are running an aluminum intake, did they restrict some of the exhaust that flows through to help with cold starts? Is there a spacer between the intake and the carb to help prevent heat transfer?

Just a couple ideas.

Tim H

Is this a 750 vacuum, 850 double pumper, 600???
I would wire the choke open and eliminate that right off the bat.
After that you need to find someone who knows Holleys to adjust the floats, idle screws and if that don't fix it you have a faulty new carb and I would send it back under warranty, because you shouldn't have to tear it apart and replace parts right now.

TimAT

Float level would be first, followed by measuring idle vacuum and seeing if your power valve is correct. If the PV is the same as the vacuum, it'll open and add fuel.

scottyp99

LOL!!! You want to get a lot of replies? Ask a carb question! Everybody loves to jump in and help diagnose a carb problem, they are just fun to mess with, even over the internet! Like solving a puzzle or something. Fortunately, almost all C3s came with a carb of some sort, so there are a lot of guys on this forum who know what they are talking about, and even the ones who don't are getting there. (Like me, for instance!) The trick with Holleys is the LIST number. It's on the front of the housing on top of the carb that holds the choke flap. Get that number, and then these guys will know exactly what carb you have, and will be able to give more specific advice. Of course, the answer to your problem may already have been posted, it's all been pretty good advice so far. My only real advice is this: If you have no idea what the problem is, and you are just checking everything, do the easiest stuff first. Check the choke first, because it's easy to do. Then set the floats, because it's pretty easy, and it needs to be done anyway, if it hasn't already been done. Same with the idle screws. Pretty much what Tim H posted. From there it gets a little more complicated. At that point, you might be best off following Tim's advice again, and just returning it. He's only messed with about a hundred different carbs in his life (90 of 'em 750 double pumpers, right Tim??) If you don't know how to do any of this stuff, say so, and someone will jump in and help you out. Ugh! I'm going to bed, man!!!


Keep the shiny side up!
Scott

69 Chevy

Since neither you, daddy or 'the mechanic' has a clue, it's best to find a mechanic who does.

Tim H

I really like 750 Holleys.
My last Holley was just plain wore out and I gave up and bought a new one and it solved about 4 different problems!
You should find someone who knows about Holleys or you will have your whole engine messed up trying to fix the carb.

Jughead

Float & choke. You shouldn't need a mechanic to do this.

cv67

Start here.
New carb? DONT start throwing parts out or bypassing them .
Fix them they arent complicated and work well
Use the stock setting they show

Then as said go to your floats bet thats your problem

Knowing a model #/size would sure help

Billysvette

Why would it be a float? It runs great cold and when it warms up ,it starts running bad. If it were the floats it would run bad all the time.Pull the choke completely off and if that doesnt fix it ,then go to the adjustments.

Street Rat

CorvetteFirstTimer

Not Properly adjusted Floats?

pawpaws toy

Check to see if the air cleaner lid isn't clamping down on the carb vent tubes. I had this happen a few years back on a new carb install. It acted just like you are describing.

69cvette

alright would a bad gas cap cause it to run like this too? because my dad failed to mention to me that the tank builds up so much pressure that when he pops it off after the car gets hot, the cap practically flys off into your hand and scares the crap outta you. i mean its insane how much pressure was built up!!

could that be making the fuel push back through to the carb making the fuel dump out?

cv67

leave the cap off and try running it in the driveway

yes I also say check the floats who knows what the mechanic did.
They shouldnt need to be touched out of the box.
THeres not much to the holleys its usually something simple.
Check the adustment on the accelerator pumps dont want too much preload on them.

All this can be done in minutes with a little research
If its a new carb no reason it cant be made to run well in a short period of time.

CorvetteFirstTimer

Only if you don't have a fuel regulator. A fuel regulator would only allow so much gas through