How much paint do I need to buy

One primer and 2-3 finish cans should be plenty. They make ceramic paints that are fuel resistant. Some of that in clear around your gas tank area over your color coats will help save the paint when you inevitably splash. Gas isn't friendly to rattle can spray paint. Several thin coats, follow the directions on the can for recoat times, and let it fully cure before you start reattaching parts.

I concur with the Mainiac, except that I"d use almost two cans of primer. Sand and sand and sand, then wash and prime the heck out of it. If you're using good stuff, that primer base will really be strong, and when you dump your bike (maybe never ) you'll be glad for it.

Personally I like using that filler primer when using rattle cans, ya still gotta spray it on in thin coats and sand in between coats, but it's great for smoothing out imperfections in thte metal like minor pitting or smoothing over welds depending on what welding method was used during manufacturing. 2 of the 14 ounce cans will be plenty enough...
Remember, the paint is only as good as the primer that's under it so don't take shortcuts during priming, and the primer coat is only as good as the surface under it so proper surface prep is what's going to make sure the primer sticks and never peels or separates.

For the color coat, 2 cans will do and you also want to apply several thin coats instead of fewer thick coats, sanding in between coats. If you're using metal flake, prismatic, or pearl colors, do NOT sand because it'll ruin the effect, just spray on thin but wet coats, let dry, then resume sanding in between coats when applying the clear.

The clear coat is what's gonna give it it's shine and protect the color coat, I prefer automotive grade 2 part clear, and if you don't have a paint gun you can still get the same results by using 2k clear that comes in a can, it has a mix charge under the can and gives you about a 24 hour window to spray it, this stuff costs about $30 per can but will give far better results than any single part rattle can clear. This stuff is actual automotive grade clear in a can and it's used by paint and body shops for small repairs etc where using a gun isn't practical, it's a little expensive, but it's the next best thing to having it professionally done at a paint shop... http://www.spraymax.com/index.php?id=361&L=1 They sell it at most auto paint supply shops but you can get it off Amazon as well... http://www.amazon.com/Spray-High-Gl...397248&sr=8-1&keywords=spraymax+2k+clear+coat
This stuff is thick so one can will most likely do the trick. I use about 4 ounces of clear, 4 ounces of reducer, and 2 ounces of catalyst to spray a motorcycle tank so a 12 ounce can of this stuff should be enough to cover the frame and fork.
Another option to having an automotive clear coat would be to talk to some of the local paint shops in your area to see if they will spray on the clear for you, most of them will charge $20 to $50 and just put the frame in with the next car they shoot since it's just a small amount of clear and spraying. You'll end up doing the sanding and buffing, but that's where you save money, and if the painter is really good it may not even need to be sanded down or buffed out.

For the clear I've found that some of the auto paint shops will do the clear on small items for really cheap since all they need to do is put it in the booth the next time they clear a vehicle, I've heard of others getting parts cleared for as low as $20 for a motorcycle tank... it never hurts to ask around and it'll be a lot better quality than any rattle can clear as well as being gasoline proof. Even that Finish1 brand clear they sell at Advance auto and a cheap Harbor Freight touch up gun can give impressive results if ya got a small compressor and a place to spray, I think last time I used that stuff it was like $25 for a quart of clear and $12 for the catalyst, and you can get a decent touch up gun from HF for under $20 if ya want to go that route

I'm gonna go against everyone here.

Hands down, the best spray paint I've ever used is Rustoleum 2X cover, from home depot.

With NO primer whatsoever.

Covered that with Rustoleum automotive clear coat spray can, also available from home depot. Best clear coat I've ever found. Gas resistant and compatible with most paints.

Painted tanks with it and splashed gas on them with no problems.

I have a sandblast cabinet so I just paint right over the bare metal.

Painted 2 motorized bikes, my 50cc motorcycle, and at least 10 bikes. All of them are highly scratch resistant, brilliant, long lasting colors.

The one bike I did prime, using rustoleum primer, was the worst paint job I did. The paint never seemed to harden, scratched just by breathing on it, and just plain sucked.

I think they finally got the formulas right. I've painted tons of bikes using every spray imaginable, and the 2X cover is so much better than anything I've ever used.

In fact, I've went back and sandblasted parts that I recently painted with it, and it was so difficult to remove I had to wipe it down with paint thinner to loosen it up so the sand would strip it.

I'm totally sold on it. Before I discovered how good it was, I woulda given the same advice as everyone above, but not anymore.

The GT2 is aluminum, right?

If it is or not, doesn't matter. If it has the factory paint on it, I'd wash it, dry it completely, and paint right over it.

One can of the 2X will cover a frame, but I'd buy two anyway.

Seriously, the bikes I've rattlecanned with the stuff have come out better than factory, and as good as any professional job I've seen.

Here's a 58 schwinn I just did. Frame, rims, chainguard, basically all the red parts used 1 1/3 cans of 2X, and one can of rustoleum auto clear coat gloss. No sanding in between coats, no buffing the clear coat. Just paint it and go. Takes about one day to cure.

And no, I'm not a spokesman for rustoleum, but I should be.

Here's the paint, my 46 schwinn dx clunker, gloss black, purple and orange darts, and detail...

The tires are a cute bubble gum pink.

Pics of my 48 dx klunker didn't show up...

Thanks Baird! I'm going to try that clear on bare metal and see if I can get it to stick. Have a vintage cruiser I want to strip and clear right over pretty much all the metal. There will be a little flat black and brass on the bike also but mostly raw.

I've cleared raw steel with it and it doesn't yellow or varnish like some others I've used.

Bairdco, thanks again for the tip. Having owned a couple small body shops over the years rattle cans never had much place in my book. Well I worked with them to learn to get the best of them a few years ago and the best I ever got was ok at best on the under carriage of a non show car ha ha. Well thanks to your tip I am doing my second complete bike with the 2X and love it. Amazing stuff, thanks again, I might never have found it.

Vansickle is the only consumer level supplier of true Alkyd Enamel in an aerosol can that I know of.
It takes longer to cure fully, but is a very tough coating when cured.
This was posted on the forum a while back, have used it myself and it is good. Make sure you have plenty of ventilation, its strong.......................Curt