what causes this ?

[harlandodge]

when i turn off my car i can start it right back up within a minute, but after it sits about 5 minutes or longer it will crank and crank and crank like its out of gas before it will start back up,,,anyone know why this happens

[RD]

gas evaporating from the bowls of the carburetor possibly, thus causing you to have to crank the engine more to pump more fuel into the carb to start the engine.  do you have a spacer between your carb and intake manifold?

[b5blue]

It could be "heat soak" the intake gets really warm/hot and drys out any fuel. Is the heat crossover blocked off? Aluminum intakes do it the worst. Could be that the flap on the passenger side exhaust manifold is stuck closed forcing to much heat into the crossover. (Among other things)  

[TylerCharger69]

I had the same problem...fuel evaporation due to excessive heat....What i did was pull my intake manifold and fabricated block off plates and installed them at the heat crossover passage  (the small holes in the center, on the sides) problem solved!!!

[Ghoste]

That's exactly what it is, modern fuels have been formulated to work in modern fuel injection systems not our obsolete carbed engines.

[R2]

might want to try a carb spacer (eg,,phenolic) under the carb,,might help.............

[b5blue]

A valley pan gasket set with the heat blocked, drill a 1/8 hole in the block off on both sides to allow a little heat to the choke well. Worked like a charm on my six pack but (at least on big block) check the paper intake gaskets for thickness as you may need thinner/thicker ones. Phenolic spacers won't stop the intake from overheating the floor of it's runners and vaporizing start-up fuel. 

[harlandodge]

i have 2 intake gaskets or valley pans one has the center hole on each side blocked off , the other one doesn't , i used the one that is open,,you guys think this could be my problem with it ?

[John_Kunkel]

It's more likely percolation than evaporation.

After shutting the hot engine down, remove the air cleaner and look down the carb bores; if you can see fuel dripping from the boosters the fuel is boiling and flooding the engine.

[RD]

It's more likely percolation than evaporation.

After shutting the hot engine down, remove the air cleaner and look down the carb bores; if you can see fuel dripping from the boosters the fuel is boiling and flooding the engine.

oooo never thought of that.. and I mean that, EVER...  let us know if this is it.

ultimately, both accomplish the same effect and are treated by cooling the temps between the intake manifold and the carburetor.

[harlandodge]

gas evaporating from the bowls of the carburetor possibly, thus causing you to have to crank the engine more to pump more fuel into the carb to start the engine.  do you have a spacer between your carb and intake manifold?

no spacer used

[RD]

gas evaporating from the bowls of the carburetor possibly, thus causing you to have to crank the engine more to pump more fuel into the carb to start the engine.  do you have a spacer between your carb and intake manifold?

no spacer used

try a spacer (plastic/phenolic not metal) first, its cheap and easy to do.  if the problem still exists, i would go with a valleypan that has the heat crossover blocked off.

[harlandodge]

its kinda of embarrassing when i come out of a quik mart or store and people are looking at my car and when i go to start it  it cranks for ever seem like

[harlandodge]

ok , thanks guys ,,i'll give some of these helpful tips a try

[harlandodge]

when i stop to get gas and take off my gas cap  it has so much pressure that it just about blows the gas cap out of my hand,,could this have anything to do with it ?i mean could this pressure keep gas forced to the carb and make it flood ?

[bobs66440]

when i stop to get gas and take off my gas cap  it has so much pressure that it just about blows the gas cap out of my hand,,could this have anything to do with it ?i mean could this pressure keep gas forced to the carb and make it flood ?

I have exactly the same issue. When it's warm the car cranks forever before it starts, but when it's cold it starts right up. And yesterday, I took off the fuel cap and there was a lot of pressure, enough that it blew the cap into my hand. I am running a dual quad setup on a Offenhauser aluminum intake. I found that when it's warm & doesn't want to start, pumping the gas does not help. If I just let it crank and give it no gas, it will eventually start after 5 seconds or so.

[resq302]

For starters, if you have a vented system and you go to take your gas cap off and it is blowing out into your hand, you have a problem there that the vent tube or something else like the vent in the cap is clogged.  We had a similar problem with our 70 el Camino SS 396 that when it got hot, it would not start once you shut it off and it cooled down.  Turned out to be vapor lock in our elky!  We found the problem was that the repro fuel line that was sent to us was the wrong one and once we got the proper routed line, it was far enough away from the block that kept it cool so it would no longer boil the gas inside the line causing the vapor lock.  Hope this might help.

[bobs66440]

For starters, if you have a vented system and you go to take your gas cap off and it is blowing out into your hand, you have a problem there that the vent tube or something else like the vent in the cap is clogged.  We had a similar problem with our 70 el Camino SS 396 that when it got hot, it would not start once you shut it off and it cooled down.  Turned out to be vapor lock in our elky!  We found the problem was that the repro fuel line that was sent to us was the wrong one and once we got the proper routed line, it was far enough away from the block that kept it cool so it would no longer boil the gas inside the line causing the vapor lock.  Hope this might help.

Well, after reading your post and the others, I think the issue (with mine anyway) is vaporlock. The fuel line & filter is run very close to the front of the motor, routed up between the alternator and the water pump. I will re-route the line & replace the vented fuel cap and see if that helps. Thanks for the info.

Bob

[B5charger]

I have a similar issue, but mine will start-up easily while it's warm.  My problem is trying to start it after it's been sitting for a while and cold.  I have to crank and press the gas a bunch of times as if I have to refill the bowls.  I could be wrong, but I think I've got the evaporation problem.

[b5blue]

The bowls fill without touching the gas...you have a choke problem.

[resq302]

I have a similar issue, but mine will start-up easily while it's warm.  My problem is trying to start it after it's been sitting for a while and cold.  I have to crank and press the gas a bunch of times as if I have to refill the bowls.  I could be wrong, but I think I've got the evaporation problem.

We have that problem too with our 70 challenger.  I attribute it to the crappy newer fuel blends that evaporate a lot faster than the older stuff.

[harlandodge]

I have a similar issue, but mine will start-up easily while it's warm.  My problem is trying to start it after it's been sitting for a while and cold.  I have to crank and press the gas a bunch of times as if I have to refill the bowls.  I could be wrong, but I think I've got the evaporation problem.

it doesn't matter if i press the gas or not on mine ,,if  my car has been driven and is hot when i turn it off and let it sit for 5 minutes or longer it cranks for a long time before starting back ,,acts like its flooded

[resq302]

You can try this, once it has sat for a while like you are saying.  With the engine off, take the air cleaner off and look down the carb and give it a couple shots of the accelerator and see if you have any squirt coming out.  If not, its a good chance that you are having vapor lock and the gas is boiled out of the carb.

[harlandodge]

ok thanks ,,will give a try