I did my tank with por15, (http://www.por15.com) seems to be working great. I cleaned the tank out with muriatic acid 80/20 solution strong. It cleaned out the tank within a few minutes. You have to plug the lines at the fuel **** port. Then release the plugs and let some acid run out to get the inside of the lines. Then put in some baking soda mixed with water and rise it out to stop the acid. Then IMMEDIATELY put in POR's prep solution. It will prepare the metal for the sealer and allow you to take your time in getting in. It has phosphoric acid in it which stabilizes the metal for a day or two..no rust. Then you pour in their sealer, slowly and careful into a part of the tank where it won't hit the screen intakes. If you do it slowly and careful you won't get any on them. Then SLOWLY rotate the tank until you've got it all covered. Again if you do carefully you can avoid any/most contact with the screens. I got the smallest can of both products the stabilizer is reusable. The sealer is not but I only put about half of the can in and it was still too much. I had to pour out about 2 oz. The less you can use the better as a deep coat or pooling is not good. I did seal up the fuel sensor hole using the locking ring and 4 layers of rubber. I painted some sealer on the sensor box later.
I would do this first! run your bike off a gas can for tuning etc. while you prepare the tank. You have to let this stuff dry for several days. Again be careful with how much you use less is more. The less you have to dump out the better as it's hard to get out because of the lip on the inside of the gas tank. Keep turning the tank until there is none of the sealer running around. If you put the tank down and let it sit for 30 seconds and look in with a flashlight you'll see the pooling if there is any..if there is start turn again or try to dump out the extra.
If you do get some on a screen you can try some compressed air through the fuel lines it may blow off the sealer.
Getting the tank out of your bike is a bit of a pain, the whole back end everything except the swing arm has to come off..and since you are that far you might as well take that off too and grease/clean the swing arm bearing etc. also change out the rear drive oil and re grease the splines with 60% moly...while you're at it.
I've tried phosphoric acid, muriatic acid, and electrolysis. Electrolysis works best for me. Cheapest, cleanest, and most effective. No coating necessary but you can still use por-15 afterward if you want.
BTW: Be glad you don't live over here in Bend. Lots of snow and ice.
I would vote for the Evapo-Rust/Rusteco method. I have used it on several motorcycle tanks and it has worked very well. As one of the previous posts mentioned it is important to get the tank inside clean and dry before using the Evapo-rust. I used very hot water and some laundry soap and TSP to clean non rust varnish and dirt off of the inside of the tank.
One of the nice things about this system is that you can clean a tank that is hard to get out in place. (Yes, Mr. Goldwing I’m talking to you) Be sure to cap off the lines to the carbs, I’m not sure what it would do but it is water based and water doesn’t burn so well.
The Evapo-rust that I used was about $20 a gallon so if you have a three gallon tank you can do the math. You can reuse the stuff a few times before it becomes ineffective. If you are in economy mode and don't want to buy enough to fill the tank then the tank will have to come out so you can move it around. All the interior surfaces need to be wet with the fluid for while to be cleaned. I just look at the inside with a penlight every few hours and it's easy to see what has been cleaned and what has not.
This is not a real fast process. It will take a day or so to clean a tank that is completely filled. Plan on longer if you are using the economy method. The product also works slower as the temperature goes down so if you’re in a cold garage you can double the time. Also this product dissolves the rust but does not coat the tank so it can re-rust if don’t keep the tank full and use some fuel stabilizer during the off riding season.
If your tank is rusted clear through and leaking the Evapo-rust will remove the rust and the leak will be worse. If your tank is that bad a coating system is about the only option.
Muriatic Acid worked for me and I did it while the tank was still mounted on the bike. I used an 80/20 solution and let it soak for about 1 hour or so. Used baking soda and water afterwards to neutralize the acid.
Also, my intake screen was rotted, mashed in, and was restricting the flow of fuel thru the intake tube. I took one of those little PVC saws and cut that screen filter off. Also, I put some magnets on the lowest areas on the tank exterior to catch any little rusty bits that I may have missed when vacuuming the tank.
I did electrolosis on one tank and rustelco on other.Tried white vinagar it was slow but worked for the time i used it.Finished the job with electrolosis.That was fun and worked great.Downside is you need a protective coating to put in it if u want a lasting rust free tank.
Oh yes! i tried the bbs too.thought i could bounce them around with shop vac in blow mode.Didnt work well really.
I thought Rustelco was the greatest of all so far.Expensive!