Dry Carb after sitting overnight

[eddy314]

I know this has been discussed before but I don't think it was ever resolved. After sitting overnight my 79 Carb is dry and takes a lot of cranking before it gets fuel. After you get it started the first time, it starts all day long right away. It happened before and after I swapped out the carb and manifold. I eliminated the little flying saucer checkvalve in the fuel feed line. I checked the fuel pump, its OK. I've heard many owners with this problem. There's got to be something causing the fuel to disappear, evaporate, or get sucked out. My 72 never had this problem and I'm sure it didn't happen when new. It seems that installing an electric fuel pump is only a workaround. Any ideas on the root cause? Thx

[Mathew26]

Check valves help and fuel pumps wear out over time allowing fuel to semp back. Those 2 would be easy things to look into esepcially since Autozone has really inexpensive check valves.

[So Cal Mark]

if the carb bowl drains, it has to be a leak from the carb. The likely culprit is a leaking accelerator pump diaphragm since the Webers don't have a separate base and middle section. It's quite impossible for the fuel in the bowl to climb up to the needle valve and find it's way back to the tank

[eddy314]

You know, that's what I keep thinking also. I don't see how the fuel could be sucked back or drained in any way. The problem is that I don't see signs of a leak anywhere especially from the accel pump. Is there any way that the accel pump could leak internally out of sight?

[So Cal Mark]

not internally, but they can leak so slightly that you don't see any wetness. Fuel evaporates quickly. After running it, run your finger under the bottom of the pump cover and check for wetness. It's common for the pump covers to warp also, causing a leak

[BEEK]

on the 79 carburator there is a vac controlled accelerator pump and a " power valve" also vac controlled, these have usually always been the cause of a dry float chamber after sitting, these are not included in most carb kist and often overlooked. im sure there is a supplier out there who has these diaphrams for sale. or put a better 32/36 carb on and enjoy. just my opinion

[ROOK1]

I have the same problem on my 71. I am fairly certain its not evaporation since my fuel line ends up being empty too. I have a factory carb, no check valve and an electric fuel pump. My thought was the carb was being siphoned dry but that would mean the bowl inlet is at the bottom of the bowl. I haven't been in the carb yet so I don't know if this is the case. Ideas?

[BEEK]

on the 71 things are a little different, \
1. the fuel does return to the tank if a check valve is not installed
2. evaporation from heat soaking will occur in the carburator
3. the accelerator pump is the only thing besides the jets in the lower part of the float chamber

the electric pump is a good way to overcome this problem. but check your check valves, the lines should not be dry

[eddy314]

Thanks for the replies. For the record I removed the original 79 vacuum assist 28/32 Carb and installed a mechanical Weber 32 ADFA. All the vacuum lines have also been removed. The problem is there both before and after the swap. I will sit up all night with it this weekend while having a beer and keep my eye on the accel pump for leaks. Another excuse for having a beer or two.

[BEEK]

watch for fuel eating langoleers. kinda small and hard to see

[brunorahl]

The heat soak is boiling the fuel. The lack of check valves is letting the fuel drain down the lines to equal the level with the fuel tank. The space in the fuel lines left by the receding fuel is filled with the gas from the boiling fuel in the carbarutor. That and the small amount of natural evaporation, leave you dry and your pump starved.

There are 2 solutions. Get some fuel rated check valves from the local auto parts store. Or get a replacement electric fuel pump from one of the Fiat parts vendors and a block off plate for your current fuel pump. Let the electric pump run for a few seconds before you crank the motor and all will be well.

[eddy314]

Follow-up: So Cal Mark nailed it, the accel pump was definitely leaking. I've replaced the rubber membrane and sanded the high spots from the cover to make a good seal. I noticed that it already minimized the hesitation on acceleration, but the real test will be when I try to start it in the morning. Will provide update.

[eddy314]

: Not perfect but starts a little quicker in the morning. Still have to crank a bit but not as bad as before. This is probably as good as it will get.

[So Cal Mark]

is the choke closing fully when cold?

[eddy314]

Yes, water activated choke is operating fine.