What is This Gunk in my Gas Tank? What's the Best Way to Clean the Tank on the Bike?

What's this crud in my gas tank? The bike has sat mostly unused for the past 10 years without gas stabilization. It's big flakes and it's gritty but doesn't have the consistency of rust. Nor does it seem to react to a magnet. The tank looks awful shiny underneath this crud. Is this just old gas varnish and precipitates?

This stuff obviously needs to come out. I'm thinking of removing the entire petcock assembly and washing out the tank through the petcock hole with water or a solvent like carb cleaner. Anyone else have advice for how to clean out a gas tank on the bike?

I found this as well: https://www.venturerider.org/forum/showthread.php?23774-Clean-a-gas-tank

Looks like a solvent is the right answer, then?

This stuff obviously needs to come out. I'm thinking of removing the entire petcock assembly and washing out the tank through the petcock hole with water or a solvent like carb cleaner.

Unfortunately, I don't believe you can remove the petcock from the tank while the tank is installed on the bike.

While the gunk LOOKS like big pieces of rust, I think it is, as you suspect, dried flakes of dislodged varnish. Fish some of the crud from the tank and experiment with different solvents. Place some of the gunk in a small container and add different solvents to determine which solvent dissolves the stuff and puts it back into a liquid solution.

Perhaps one of the most effective ways to really clean out a tank, but not an easy way, is to remove the tank and put about 5 pounds of galvanized roofing nails in it, seal it up and play shake the can with a few friends for about an hour or so. When you're done then remove the roofing nails and give the tank a good flush with some sort of solvent. Myself, I would cote the tank with red cote or cream or any of the coating products out there...

IMHE (inventing some new Code verbage here = In My Humble Experience), rust is not magnetic.. That said,, what I would do first thing is, if you can (never owned a 2nd Gen), stick my finger in the filler hole check the ceiling of the tank for actual rusting - if the ol finger thru the filler cant work = dental mirror and a flash light. If we are dealing with actual rust = sealing of the tank is mandatory..

If this is the case, you will have to remove the tank, hit it with muratic acid, neutralize and rinse out the acid real well and then seal it with Red-Kote tank liner.. Have used many other methods but Red Kote is the best of the best and I wouldnt waste my time with the other stuff,, again,, IMHE.

If that gook turns out to actually be just dried/laqured fuel and we are not talking rust here,, I would use good old cheap and safe/simple to clean up White Vinegar.. Just completely drain the tank and top the tank off with a few gallons of the vinegar and let it set a few days.. I have seen that stuff clean up some pretty nasty tanks to useable, not necessary to seal level of useage PLUS vinegar is easier on the paint so totally useable with the tank still on the bike..

Thanks, Scott! I can usually get rust to dance on a magnet because there's usually some ferrous material still mixed in with the ferrous oxide. Appreciate the comment about using white vinegar, too. I think I'll suck out what I can and then fill the tank to the tippy top with vinegar and let it sit. 7 gallons of vinegar is pretty cheap.

Be careful with the vinegar also, while it might not harm most paint it will dissolve aluminum. Google "dissolving aluminum in vinegar".

We just went thru this this week where I work, some customers thought it would be a good idea to clean their machines with vinegar and completely dissolved a critical aluminum part, it took us a while to figure out why some machines were failing until we sat down and went thru their setup use and clean up procedure and they mentioned the vinegar to get it cleaner, and then it still took a couple days for the light to go on that is was the vinegar.

After your tank is clean that will make a lot of salads..........

I decided to test different solvents on that varnish/precipitate before doing anything. I soaked the flakes in little containers for awhile. Neither vinegar nor carb cleaner nor fresh gasoline did a thing to it.

I went to Plan B:

• The entire petcock assembly does indeed come out from the bottom by snaking it to one side of the swing arm. I have the rear tire off, so that helped, too. The petcock pick-up tube filter screens were covered with the nasty gunk and had to be cleaned.
  
• I left the fuel level sensor out for several days so the tank would completely dry.
  
• The varnish turned into a dry layer of flaky scum that was easy to knock off the inner surface.
  
• I used a retrieval tool (because it's spring-like and flexible) down through the float hole to knock loose any extra thick stuff.
  
• I also used a Campbell Hausfeld air nozzle tool to reach down inside. On close contact, it easily blew the gunk loose.
  
• 
  
• Then I stuck my Shop Vac blower nozzle over the fuel filler neck and blew a ton of air down into the tank, which made all the gunk go airborne inside the tank like a dust storm. Using the air nozzle tool down through the float hole also helped keep everything swirling and airborne.
  
• I stuck another smaller Shop Vac suction nozzle down through the float hole and sucked up all the airborne particles. Worked like a charm.
  
• I expect any remaining amount over time to be stopped either by the screen filters on the petcock or by the fuel filter itself. I can pull the float valve in the future to see if more cleaning needs to take place.