gas guzzling 72 demon...kind of long sorry

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billytuffnuts

billytuffnuts

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Well after years of owning my 72 demon and driving it only a few hundred miles I finally went out and fixed my broken gas gauge by replacing the sending unit.

I took the maiden voyage to my local gas station and filled her up. I think it took around 13 gallons or so (it was basically empty at this point) but can't remember the exact number, but the gauge went to full. I was excited to finally have a working gas gauge and not having to worry about diagnosing a 'no start' condition again only to realize I just ran out of gas.

I took it around the block a few times since I was out and brought it home. Since then I've really only had it running maybe 30-40 minutes idling in the garage working on it. Just took it out again around the block again to work out some kinks and noticed the gauge was already down to 3/4 full! I have a stock 360 magnum engine with an air gap intake, headers, and a holley 650 vac secondaries w/3.23 gears. I know I'm not going to be getting 30mpg (nor do I care all that much) but a 1/4 tank of gas that quick!? How?? Then I got to thinking...

The 72 demon is originally a /6 car with all the emissions crap, which was promptly removed when the 360 went in. Well when replacing the sending unit, I noticed that there was an additional steel line coming out of the gas tank at the top (presumably for the charcoal canister?).

Is it possible that all that gas is evaporating through that line? Can I plug it or is that needed regardless? I don't believe I have a vented gas cap but not positive...Any ideas guys?
 
Yes I do believe that the extra line was for the canister,and I would cap it off to keep contaminants out.As far as evaporating through that, it is an awfully small opening I don't think it would evaporate that much.
 
the evaporation part is very possible and very likely, dont plug that line!!! If you don't have a vented cap you will starve your carb or even cave in the tank...,your best bet is to install another canister. I also had a /6 and now its a 360 with about 325 HP and I used the old canister. (stock HP is around 265 with the 4 barrel, just a little more than stock, just enough to make it fun)
 
leblanc said:
the evaporation part is very possible and very likely, dont plug that line!!! If you don't have a vented cap you will starve your carb or even cave in the tank...,your best bet is to install another canister. I also had a /6 and now its a 360 with about 325 HP and I used the old canister. (stock HP is around 265 with the 4 barrel, just a little more than stock, just enough to make it fun)
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dont expect great mileage out of your Demon.........
I have a nice Yugo to trade if you like! :snakeman:

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I lost the steel tank and went with a 15 gallon fuel cell mounted in the trunk. Nice thing about the fuel cell is I can pull up to any pump and also just need to open the cap to check the fuel level. Another added benefit is that no one can siphon out any fuel. it is locked in the trunk!!!!! Left the fuel tube and cap on the car so it looks stock. My car gets about 18 MPG on the highway and 15 in the city so I can pretty much plan on how many miles before I will need to stop for fuel. I had a sending unit for my fuel cell but it burned up with my home last year and I have not had the $ to get another one as of yet.
 
HemiMark said:
dont expect great mileage out of your Demon.........
I have a nice Yugo to trade if you like! :snakeman:
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ever considered removing the hemi and "convincing" it to go into the Yugo???:toothy10::toothy10::toothy10:
 
Ok I'm hearing plug the line and don't plug the line...

If I were to plug that line and then get a vented gas cap would I be in the same situation I'm in now or are the caps somehow metered? What does a vented cap look like by the way, just want to check and see if I have one or not. Mine is the stock painted body color cap that came with the car.

If I don't plug the line, leblanc says to put back the charcoal cansiter. I suppose that would be the correct way to do things however I'm not a fan of those emission parts in my engine bay.

Surely I'm not the only one who has removed all emission parts, what did everybody else do with that line that originally went to the charcoal canister??

A little update. I just got back from a trip to walmart (approx 1.6 miles each way) and it used a 1/4 tank of gas lol jesus. I did forget to mention that I have the lokar kickdown cable kit and it is properly adjusted as written by the instructions. However I do seem to have the same problem a lot of people have with a late 3rd shift (have to be up around 50-60+ for it to kick into 3rd which doesnt happen much for crusing around). so basically I'm driving in 1 and 2 most of the time which could also attribute to this.

I ordered the bouchillon performance kit yesterday and hopefully it will correct this as it has with others instead of drilling out new holes in the TP lever for the lokar.
 
I'm also getting a slight stumble when starting from a stop. It feels like I need to ease into the gas or else it will die.
 
I guess I didn't read into it far enough,no I wouldn't cap it off it's not vented.Sorry for the bad info.One question though is there a small tube that comes out of the tank and runs along side the filler tube? If so that is your vent. I don't know if they ran one this way with emissions or not.
 
mopardads67 said:
I guess I didn't read into it far enough,no I wouldn't cap it off it's not vented.Sorry for the bad info.One question though is there a small tube that comes out of the tank and runs along side the filler tube? If so that is your vent. I don't know if they ran one this way with emissions or not.
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I'll have to check on that. I didn't notice it last time I was underneath the car but I also wasn't looking for that.
 
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