Fuel Drain

[wright young]

Just completed restoration of '73 Challenger Rallye 340. It runs great and have won Best Original & Best Mopar at three shows. I have only one problem I can't solve. If it sets for a couple of days, when I try to start it I have to crank & crank until fuel is pulled all the way from the tank, It seems, before it will start. I replaced the original Thermaquad carburator with a re-built Thermaquad & I still have the problem. For some reason , the fuel drains out of the carburator & back to the tank if it sets for a few days. Somebody help!

[72Challenger]

I had the same problem. Turned out to be two problems - leaky gaskets in the carb and a very small leak in the fuel pump diaphram. Not bad enough to be noticed while running, but after a week of sitting I needed to prime the carb.

I thought the '73 Rallye was a 360?

[wright young]

'72 Challenger, thanks for the reply. The '73 Rallye was still the "Mini Hemi" 340.
I installed a new fuel pump in case it was a leaky diaphragm, so I guess the only thing left is the leaky carburator gaskets. I guess I'll have to entertain buying a new different brand carburator, however, I would like to keep it "stock". I have discussed this with quite a few Mopar 340 owners & they all have the same problem. I have been told it is a characteristic of the "Thermoquad".The Thermoquad performs great in all other aspects. Do you have the Thermoquad & if so was it difficult to replace the gaskets?

[70Barracuda]

I have an edelbrock and it does the same thing. About a week and its crank time!

[72Challenger]

No, I had the Holley 2-barrel. "Fixed" the problem with an Edelbrock and an electric pump during the rebuild. I think the problem is still there really, because after sitting a few days it still takes the electric pump a couple seconds to build up pressure. I just don't need to open the hood any more!

I think that the fuel is actually being siphoned into the manifold. My leaks are gone, and there's no way the bowl could be leaking back into the tank. But it's going somewhere. So I think internal fuel passages are slowly draining it away.

[ehostler]

I've had the same problem on my big blocks (383 & 440). Let them sit for more than 2 or 3 days and they have to crank a little, before there is enough fuel in the carb to start it. The only way that I've ever been able to overcome the problem is with an electric fuel pump. Rebuilding carbs or replacing with new carbs never fixed the problem. Same goes for replacing the mechanicle fuel pump.

[70Barracuda]

do do do do, do do do do.
you have now entered the world of the mysterous vanishing gasoline!

We don't know where it goes. We just know it's not there.

[1972roadrunner]

i would definintly go with an electic fuel pump. when changing carbs or whatever just turn it on and theres not any problem fillin the carb. i think they are worth the money, as long as you get a good one....(holley or carter, or sumthin w/at least 7-8 psi and regulator works great for me...)

[swingin72]

My 72 Dart with Edelbroch carb is the same way. I'm sure the old mechanical fuel pump is tired and that is probably the culprit. It's gonna be hell getting the thing to start in the next few days after a couple of weeks in the garage getting a new front end rebuild, torsion bars, sway bars... It's hard enough after sitting 2 days!

-Steve

[1972roadrunner]

electric fuel pump! go w/electric fuel pump! DO IT! COME ON, YOU CAN DO IT!

[wright young]

Thanks everybody for the info. I think the electric fuel pump is the answer.
I am a new member of Moparchat, and it's great knowing all of that Mopar knowledge is out there. I have been searching for a Mopar chat site for some time and just happen to stumble across Moparchat.
Will talk to all of you soon.

Mopar or Nopar

[rb77413]

Claim another one to the vanishing fuel A trick I found is to manually close the choke on my van and it starts up quicker, however I am not keeping the doghouse off, ultimate heater, and is a pain to take off every other day.