Non Clipper Dodge question

[Horst]

Need some ideas guys......
My 78 dodge truck, 1/2 ton, slant 6, 225cu in.
Did a major tune-up, replaced carb with new/rebuilt one, new coil, plugs, wires, etc., etc.

Runs great.......BUT......got 8.9mpg!!! in around town driving on the first mileage check since major tune-up - what the heck!!!

This truck always got 15/16 in town and 20 on the highway - even when neglected for months at a time!
I checked PVC - ok, the distributor advancing properly, carb functioning properly, heat riser moving freely, fuel pump not leaking externally or into the crankcase.............but...........I do smell gas....but I can't find the source of the smell!!! Making be nuts. Seems to be coming from under the rig - but I checked tank - and not leaking (at least not that i can see) then the smell goes away....then after it's been running for a while.....and I turn it off..........the smell comes back....not from engine compartment either....grrrrggghh!!!!
Any ideas or suggestions greatly appreciated.
Maybe someone has been stealing my gas at night??

[pop427]

Horst, Make sure the the EGR valve and system is working properly. The ECS is the first place I would look at for a gas smell. Look at the vacuum hoses and make sure they are hooked up the same way they were before and in good shape. How does it run as far as power and pulling go? Why did you do the major tune up? Having tuned up hundreds of slant 6 mopars I would look at everything that you did if it ran good before. Like my mother used to say " last one to touch it is responsible for it".
Doug Odom

[19julien59]

Didn't some of these vehicles have a "gas vapor filtration canister" (not sure of the full name) that can get saturated and mess things up...as well as smelling? 

[Horst]

Thanks for the responses guys- I found it (finally)

Not sure what it is - hoping just a cracked hose or line - but it is leaking at the top of the tank, where the sending unit and all the lines come in - only leaks when running - so it's happening when the fuel pump is pulling gas.

There is a 1 inch gap between the cab and the bed on the truck - and over the years all kids of leaves, pine needles, etc. dropped in there and collected - right where all those fittings are, on top of the gas tank - thus when it leaked - all that stuff soaks up the gas and prevents it from running down the side of the tank.
Anyways - I blew it all out and now I can feel gas up there after the truck is running......just can't quite see/feel exactly where it's coming from.........

so - looks like I'll be dropping the tank.......like that Jets linebacker said....."can't wait!"

(actually, I'm not looking forward to this job - I'm off to a rough start - can't even siphon the gas out of the tank - two  sharp turns and too long a feed before the filler hose finally gets into the tank - none of my siphon hoses reach/work....grrrggh!)