LS swap and charcoal canister
 

I have a 72 k10 with a 5.3/4L80e combo.

When I purchased the vehicle it had the 350/th350 with a "custom" auxiliary tank rigged up. I had a new 21 gallon tank put in and left the aux tank in but not using it. When it gets hot and the the main tank is anywhere past half the fuel pours out of the auxiliary tank fill hose that's capped off.

I know I can just completely disconnect it or plug the large fills out with an expansion type plug but my question is, is anyone else running a vapor canister?

My thought is if there is enough pressure to send the fuel to my aux tank and out the full hose and I just cap it, it will find the next weakest point eventually ruining or over pressurizing lines to the motor, etc.

Am I wrong? Is it needed or cap it and send it?
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Re: LS swap and charcoal canister
 

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I would say that the vapor canister is not doing it's job or something is capped off or plugged up on the system. Get a vented gas cap and put it on, see if that cures the problem....

LockDoc

Re: LS swap and charcoal canister
 

I'm pretty sure I don't have a canister but I do have the vented cap
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Re: LS swap and charcoal canister
 

do you have an in-tank fuel pump?

Re: LS swap and charcoal canister
 

Negative.
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Re: LS swap and charcoal canister
 

The vapor canister is located beside the battery behind the right headlamp.

It sounds like the tank is getting pressurized. Do you have a fuel return line on your setup? Or is it a single line?