Gas Evaporating out of Carb

[Sixt8Chrgr]

I know this has been beaten to death, but I want to make sure I am not missing anything. I just finished restoring my 69 back to stock. 69 RT 440 automatic, air, original carb intake, vapor canister vapor return line etc. When I drive the car and let it sit overnight I have to prime the carb to get it to start. Prior to restoring the carb, I had the same carb, intake setup but did not have the vapor canister or return line. That had been removed and a rubber hose was used from the fuel pump up to a section of tube that screwed into the carb. I don't know what type of fuel pump I had before the engine was rebuilt. The new fuel pump is a garden variety from NAPA. I am wondering if the fuel is draining back into the system via the fuel pump, or is evaporating or what is going on. I am not having this issue with my other old cars and I burn the same 93 octane 10% ethanol Shell fuel. I do have an aluminum spacer plate under the carb between carb and intake. Same as I had prior to the rebuild. Car use to fire right up after sitting for a long time, but like I said not now.

Any thoughts?

[green69rt]

Nobody else chimed in so I'll start.  I take it from your note that you rebuilt your carb.  That's where I'd start.  Leaking gasket or some other thing that is allowing the bowls to drain (maybe into the intake.)  Probably means you're going to have to take it off again.  I really can't imagine any way the bowls would drain back down the line.  Original AVS carb?

[Sixt8Chrgr]

Yea original AVS carb. I saw the post about under hood temps after I posted my thread. I believe my crossover is not blocked so that is probably contributed to my issue as well as the fuel pipes being close to the engine. I know I still have some winter blend fuel in my car which does not help either.

[70sixpkrt]

I have the same problem after 3 weeks or more of sitting on my sixpack. I think it's todays gas that is evaporating quickly but how do you know if you have a leaking gasket and it is draining into the intake?

[green69rt]

I have the same problem after 3 weeks or more of sitting on my sixpack. I think it's todays gas that is evaporating quickly but how do you know if you have a leaking gasket and it is draining into the intake?

Yeah, that's why I said that he might have to remove the carb, fill the bowls with gas and then set it on a piece of cardboard to see if anything shows up.   

[c00nhunterjoe]

1 week let alone 3 is more then enough to evaporate any kind of gas.

[green69rt]

1 week let alone 3 is more then enough to evaporate any kind of gas.

Yeah, but he said this is happening overnight.  70sixpkrt might be waiting a long time but sixt8charger seems to have a legit problem.   On my old charger, I would go to sea and let my car sit for weeks, sometimes a couple of months, and it would usually fire up pretty easily with the original AVS.   Something is going on.

[c00nhunterjoe]

Fuel cant drain backwards out of the carb to the tank. It is most likely evaporating overnight. It is an open system and normal. If the carb were physically leaking, simply looking down the bores after it is shut off would show if it were dripping.

[Sixt8Chrgr]

Before I restored the car I did not have this problem. Same engine, same carb. What I changed, I installed a vapor return line and I installed the factory correct fuel pipe. I did have a rubber hose from the fuel pump to the carb.

[b5blue]

Are you guessing the fuel is gone or did you open it up and look? With today's fuel the heat should be blocked from the manifold but I'd look closely at the choke setting. 

[Challenger340]

Our '69 R/T Carburetor sometimes goes dry as well after sitting a few weeks/month ? but all it takes is about 5-6 seconds cranking, then pump the pedal a few times, crank again and it starts right away.

Are you saying you have to manually prime the Carbs after sitting ? or that it will not refill the Carb after sitting ?

[Sixt8Chrgr]

I have to manually put gas in the carb. Maybe the fuel pump is junk?

[b5blue]

Cranking speed, pump volume and pressure all have to overcome a bit of bleed from the return at start. Check fuel pressure when restart is the problem. 

[69wannabe]

Just had this problem on my dad's ford truck, it's an old 72 F100 with the 390 in it and it kept getting harder and harder to get it started in the morning and finally it wouldn't start at all. I could pour some gas down the carb and prime it and it would start and stay running but if it sat for a few hours it wouldn't start back up unless I poured gas down it again. Ordered a 6905 carter mechanical street pump for it and bolted it up on there and haven't had any problems since. The old pump was a regular parts store pump and I could pump it with my hand's easily it was so weak. The good carter pump brought it back to life and then some. The part number for a big block mopar is a 6903 i'm pretty sure and mancini racing is the only one that sells them I think but I may be wrong about that but they are great pumps. The only other thing about a big block mopar is the fuel pump push rod could also be worn and cause a fuel pump/ pressure issue so keep that in mind too....

[Sixt8Chrgr]

Thanks guys. I have had a suspicion that the fuel pump was bad. The car had no problem before the resto and am using the same carb but am using a return line. The fuel pump on the car is a napa brand...not sure which one. I had a nice Carter fuel pump on my 68. Will contact Mancini in the morning and get another pump. I hope that is the problem. If not will change out the rod.