When my car (-69, 307 w/ 2bbl carb) sits for about a day or so, it seems like the carburetor dries out. Every time I start it after it has been sitting for a while, I have to crank it for quite a while. It's not really a cold start problem, because once there's gas in the carb it fires up right away. The carb is a factory rebuild and there are no signs of leaks. I can't smell any gas in the garage, so I don't think it's evaporating through the carburetor either. The gas just disappears somewhere, but I don't have a clue where it's going or why. Any ideas?

Bad check valves in the fuel pump. Gas siphons down to the level of fuel in the tank. Takes forever to pump it back to the carb.

Try this: Buy a paper fuel filter to fit in the carb--the kind with the silly "safety valve" installed. (not all paper filters have the safety valve, but any "real" parts store will have the safety valve kind) IF the problem goes away, you need a new fuel pump. Note that the pump may pass the traditional tests for pressure 'n' volume. Those check valves can leak very slowly, and still cause a problem after a day or two of sitting.

Second guess, and just because it's a common problem on older cars: rotted rubber, or pinholed steel fuel hose on the suction side of the pump. You have air leaks into the fuel system. Perhaps the bowl isn't full of fuel after a day, because it never was truly full, the pump is sucking air.

I'm ruling out choke issues because you say it starts right up if there's fuel in the bowl.

I replaced the fuel pump quite recently, but it could still be bad (it's a cheapo from Auto Zone). Considering the time I have to crank, the fuel bowl must be almost totally empty so I think it's a siphoning problem. I was thinking about getting a brake hose clamp and clamp the fuel hose right before the pump before I park it. That should tell me if any gas is going back to the tank or not. Should also be fairly easy to pressure test the fuel line.

I have heard this explaination before, but knowing carburetors pretty good I cannot understand how all the fuel would be siphoned out of the bowl. The fuel inlet is usually at the top and it would be impossible to "suck" the fuel out much lower than the inlet level. I would lean more towards something being wrong with the carb. Q-jets are famous for the fuel bowl plugs leaking and they run dry overnight. Maybe the 2bbl is doing the same thing. Your idea of clamping the fuel line should confirm it either way. Let us know what you find. By the way, the easy way to clamp the fuel line is with a pair of needle nose vice grip pliers. Just tighten them enough to clamp the hose shut without "hurting" it. Use them all the time.

I have been thinking the same thing, Bill. Just hate to think that there's something wrong with a factory rebuilt carb :( I might just have to take my old one apart and rebuild it myself.

Anyway, happened to find a neat little tool (http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&pid=00947050000) at Sears today, so I clamped the hose right after I parked the car. We'll see what happens tomorrow.

Check for a sticking float needle. Had the same thing happen on my rebuilt 2 barrel on my 68 307. If you tapped on the float bowl the needle would "un-stick" and start right up. Replaced it with one I had in a rebuild kit, never happened again.

Ok, hopefully good news: I took the clamp off this afternoon, and the car started right away. I won't rule out the carb yet, so I put the clamp back to let it sit for another couple of days.

To be honest, I didn't know that there's supposed to be a check valve in the fuel pump. Do they all come with that, or is it possible that the cheapos (like mine) come without it? Doesn't matter really, if the pump is the problem, I'll just buy a good quality unit. It would be interesting to know anyway.

I am following your thread here with interest. My 72 Sprint acts exactly like yours. It has an edelbrock carb though. But a few months ago, and I am not sure but it might be when this problem started, I too replaced the fuel pump with one from autozone. I bought the cheap one .....

Now I am thinking maybe I should spend the money and get an edelbrock fuel pump.

I am waitng till you figure it out lol

I know if the air bleeds get blocked off on a Holley or Demon(others the same?),when you shut the engine off the fuel siphons out of the fuel bowls and into the manifold.The air bleeds vave to be clean to work as a siphon break.Smell your oil for fuel,I lost a crank because of this on my truck.

My '79 K10 will do that after sitting for a week, but it's usually fine within a day or two. Cheapo Checkers pump into it recently. Q-jet rebuilt a month ago. Epoxied all of the plugs, including the big one in front. Don't have a wet carb anymore, and it seems to run just a little better than before. :cool:

The car has been sitting for two days with the clamp on, and I just took it of and tried again. Fired up after a few turns on the starter graemlins/hurray.gif

Seems like the fuel pump is the problem. Sure is strange that it can siphon the gas, I just looked at the carburetor and the inlet is on top of the fuel bowl, like on most carbs. Maybe the bowl dries out for other reasons, but the fuel that's still in the line between the pump and the carb is enough to get it going quickly. Who knows, I will shop for a better one this weekend, and if I remember, I'll post an update after it's installed. Thanks for all the replies guys, you're great graemlins/beers.gif

The fuel line or pump cannot siphon fuel out of a carburetor, it's physically impossible. As Bill stated, it could not drop below the inlet level. If the bowl is going dry, and there is no sign of an external leak, the carb has an internal leak. There is plenty of fuel in a full bowl to start the engine, and it takes only a second for the pump to refill the bowl. Steve

I'm aware of that, so there could very well be several reasons for the problem. But if the clamp helps, I'm sure that a functional check valve will help too. And if changing the fuel pump cures the problem, I'll leave it at that. There could be something wrong with the carb too, but if it doesn't cause any problems I'm not going to worry about it.

Was wondering if you switched out the fuel pump yet? I am sure curious as to it that works, If it does mine will be next.

Nope, had to order it. Thought I could just go to NAPA and pick up a better one, but found out that the fitting on the pressure side is smaller on a -69 307 pump than on the "one-size-fits-all" SB pumps. Will probably have it done this weekend.

I put a new pump in it 3 days ago, started the engine and let it run for a couple of minutes to make sure everything worked. This afternoon, I took the air cleaner off to see if there was any gas left in the carb and got a good squirt when I moved the throttle. Put the air cleaner back on and cranked the starter, and it fired up immediately graemlins/hurray.gif

The old pump was a $13 "no-name" from Auto Zone, and the new one is a Carter unit (NAPA # M4513). This seems to be a special pump for 307's but they have similar pumps for other applications. I paid about $20 for it, so it wasn't expensive at all. Especially considering that it works smile.gif

I still don't know how the gas could be drained from the carburetor bowl. Still, when I took the old pump off I noticed that there was no gas at all in the line to the carb and just a little in the pump. The carburetor was empty as well.

Well, it works now and that's what matters. Thanks again for the help! graemlins/thumbsup.gif

glad to hear it, I am off to NAPA tomorrow!

Do you have air conditioning on yours? I do, just need to know if I need a different number than yours.

Don't have an A/C, but that shouldn't make a difference, should it? They didn't ask when I ordered the pump anyway, I saw the book and all it said was "1969, 307" in the Chevelle section. Safest thing to do is to just give them the number and ask for a similar pump for your engine.

Post an update when you're done, will be interesting to see if it works for you too!

I pick my pump up tomorrow, not sure if I will get it on before the weekend, but I will keep you updated. They guy looked it up and yes the a/c required a different pump, in fact he commented it had a real high PSI, maybe that is what is wrong with the one I got at the other place.