does anyone know how long it takes gas to evaporate out of a carb?

im having a problem on a project. seems like it cranks way to long for my car to start. i replaced the carb with a new one and its still the same. i drive it one day and within a few days of sitting, it wont start until i pour gas down the carb and it fires right up. it takes a good 10-15 secs of constant cranking and pedal pumping to get it to start. sometimes the battery cables to smoke from cranking so long !

what the hell can cause this? i thought weak spark but it starts right if i pour gas in. i thought maybe the fuel pump might not be holding fuel, but the carb should be holding it?

thoughts????

 

Over a period of several days, yeah, it can evaporate out. Just make sure it's not leaking out. I take the carb after running it, remove it from the engine (keeping it level), dry off the bottom and let it sit on a paper towel for a few hours. If the towel is still dry when you come back, it's not leaking.

That's one good thing about electric fuel pumps- you can turn them on before cranking the key and prime the fuel bowl(s).

Still, your problem seems excessive even if the carb is dry. Take off the fuel line (after it's been sitting a few days) and see how long it takes to pump some gas out of it, cranking on the starter. It should NOT take 15 seconds.

Weak fuel pump, a little pinhole further back in the line allowing air to be drawn in on the suction side, pulling a slight vacuum in the tank (improper venting).... could be anything. Just gotta start whittling down the possibilites.

 

^^^This^^^

Virtually ALL Q-Jets eventually leak at the bottom of the fuel bowl. Pretty much inevitable. The spun-in aluminum plugs are a sufficiently dissimilar metal to the chinesium the bowl is cast from, to create electrolysis; and ANY moisture that gets in there, which of course is impossible to prevent around a hydrocarbon-burning engine, causes them to create a little battery. The chinesium becomes the anode and erodes. When that happens, the lowest points of the fuel bowl become exposed to intake manifold vacuum; not only does the carb leak down when sitting, but WORSE, the intake vacuum literally SUCKS (yeah, vacuum SUCKS, almost as much as gravity) fuel out of the bowl and into the intake, especially at idle and cruise (high-vacuum situations), which makes the car use gas shamelessly.

If I were the betting kind, I'd bet that your carb has reached that stage.

 

When you say "new" , do you mean brand new out of the box new or do you mean new to the car (but used) ? Cause if it is a brand new carb and its still doing the exact same thing It may be reasonable to suspect that the problem lies elsewhere . I wonder , have you checked the cylinder's compression ? I ask only because low compression can be one thing that can make an engine need an excessive amount of fuel to start . There is no way the fuel should evaporate out of the bowl in as little as a few days , christ my lawn equipment sits months on end with the same fuel in their always vented to the atmosphere fuel bowls and they start up with no problems whatsoever . Don't most modern day carbs on cars such as ours have a valve whereby the atmospheric vent is supposed to be closed when the engine isn't running ? How are the chokes on these two carbs , adjusted properly ? Timing ? A timing setting too late (retarded) can make an engine need more fuel to start .

 

the problems is on my 68 442. so the car only comes in the summer time. the carb is a new reman one from holley. i will have to try taking the fuel line off the carb and see how long it takes to come out. i think the timing is good but have to check it again

 

just found out that my carburetor, a brand new quadrajet was overflowing from raw unburned fuel. I mean the whole 4 barrels were overflowing.
my Camaro is a 1982, with no electric pump inside gas tank. now it does, the sending unit with electric pump was from a 1986, brand new. I never had any flooding problem until I installed new electric pump in tank, am I supposed to use a fuel regulator? I run my fuel line to fuel pump on the engine then to carburetor. it flooded. I ran direct line from fuel line to carburetor. still flooding. I realized return line might not work properly. but it s hard to believe that the hose that goes to charcoal canister from valve head cover were wet with fuel. it has a T connection on valve head cover that intersect with a hose from a fuel bowl vacuum hose and charcoal canister. is regulator required? my carb Is not a fuel injector. think 1982. all manual.
I am at a loss. please help.

 

I think anytime you put a electric pump on, you need a regulator to get the pressure down

 

Thought so. you and many others had mentioned the same. I hope I didn't blew out the carburetor gaskets. gas were coming through everywhere outward. thanks. I am sure carburetor only need 7 psi, instead of 14 for fuelie?

 

6 PSI for a QJet.

Don't worry. You didn't hurt a thing. The excessive pressure just overcame the bouyancy of the float and pushed past the inlet valve. Then it spewed out of every hole, orifice and vent on the carb as it overfilled the fuel bowl. It looks scary as all get-out, but it won't hurt the carb at all.