Welding and Metalworking - Adding gas to a flux core welder

I'm working with a Campbell Hausfeld Flux Core 80 welding machine and have got to do something to get better welds from it.
Right now when the weld is laid and then knocked down with a grinder, I find alot of cavities / air pockets. Plus, the weld isn't very willing to sink into and fill cracks when trying to join two pieces of sheetmetal. Am I right in thinking that gas is the answer?
In the rear of the welder is a cut-out for a bottle, but no hookup lines, so is it possible there are lines inside that just need to be dug out and hooked up or is this unit simply not wired for gas applications? If not, what do I need to do set it up for gas or is this not an option? Maybe selling and starting with a different unit would be the best solution ???

There appear to be several different models that sport the Flux Core 80 name.
Some are listed as Mig/Flux Core 80 which come with the gas regulator and electrical connections in the machine to make gas welding happen.
The instructions for yours should tell you what you have.

My personal opinion is that a welder like this is a purchase that should last many years and I do not feel these homeowner units are a good investment because of their quality and availability of replacement parts.
Also, the maximum amperage and duty cycle of a machine that is suppose to operate on a 15 amp 120 volt receptacle would make it too frustrating to weld anything much more than sheet metal.

And yes, sheet metal is better welded with gas as it tends to cool the material and allows slightly more current without burning through.
You might want to try a start and stop or stitch technique to allow a bit more heat in one spot.

I have also seen the mig/flux models offered and notice that mine is different in that it only sports the "flux core" name as oppose to the "mig/flux" model.

The instructions that came with the unit have no mention of hooking up gas. So would it be best & cheaper to sell this welder and upgrade, or can I modify this piece (if possible) to accept gas for less than the cost of an upgrade?

You would need to carefully read the instructions for your unit to be sure you can even connect gas to it.
The unit needs to be able to operate the gas solenoid and a place to hook up the gas.
You would have to price out the parts to know which way to go.

If it is not possible to adapt yours it would be better IMO to get a small Miller or Hobart.

Are you using a gasless flux cored wire? gasless cored wire is available but its not cheap

You have probably already made your move, but here is a link to a re-badged Century welder, that I had previously given up on, and converted. I also have a Miller 135, so did not need a regulator. Works OK now but they are definately limited in their capacity, good for sheet metal repairs.

http://thumb5.webshots.net/t/24/665/4/8/20/2799408200059214605gefKhO_th.jpg (http://home-and-garden.webshots.com/photo/2799408200059214605gefKhO)