81 GS850G fuel tank looks like a sewer pipe

[Guest]

I just bought a couple of GS850s the other day and the G model fuel tank is really nasty looking inside. Doesn't really look like rust to me, although I'm sure there is some rust in there. It looks more like dried varnished gasoline. I've never had too much luck with using electrolysis on rusty tanks. Was thinking of trying muriatic acid this time to see if that will clean the varnish.

Chemicals available to me are lacquer thinner, kerosene, white vinegar and muriatic acid.

Any suggestions?

[mikerophone]

I've used vinegar and Evaporust in the past with good success, and one of my tanks sat with gas in it for 23 years.

Once you get down to metal the electrolysis will be more effective.

[jdvorchak]

Thought I'd post a couple of pics of the tank. Notice that it doesn't really look like rust. It almost looks like wrinkle finish paint and that's why I think it's varnished gas.





I hope these pics aren't too big. I can post a thumbnail of I need to.

[gustovh]

Try putting a bit of gas in it ans slosh it a round a see what happens, cap it and leave it over night, just might work.

V

[Nessism]

Looks like a tank liner. Not a very good one at that because it's chipping off.

To clean varnish you need something like carb dip. Not acid. POR-15 sells a variety of products with which to refurbish fuel tanks. You might want to check them out.

[jdvorchak]

Looks like a tank liner. Not a very good one at that because it's chipping off.

To clean varnish you need something like carb dip. Not acid. POR-15 sells a variety of products with which to refurbish fuel tanks. You might want to check them out.

I didn't think about a "liner". Never used one so I'm not familiar with it. At least where the liner is chipped off it's shiny underneath. That is why I thought it was just dried gas. Note the difference between the surface rust around the filler cap and the brown stuff in the tank. It is quit different. I'll experiment with some different chemicals on cotton swabs on the area I can see through the filler. Might just be varnish and paint thinner or gasoline will dissolve it. Anyway not in too big of a hurry right now. Still limping bad from my pulled muscle so for now just taking it easy and still evaluating what next. Well I know what next. Pull the tank and the carbs and rebuild them. If the tank looks like that imagine what the carb bowls look like...

[Buffalo Bill]

I would not put acid in there, it will eat through the exposed steel and may not effect the tank liner.

[Grimly]

I suspect it's a failed old tank coating; some of them weren't very good and didn't stand the test of time. For sure, if that wrinkly mess isn't removed it will just cause endless amounts of hassle when it flakes off in the future.
In the absence of knowing what solvent would actually work, it might be an idea to try mechanical dislodgement first - handful of nuts (threaded type, not acorn-ish) or pebbles and rattle it around inside with some kero for a couple of hours in total. Some people have had some success with wrapping a sealed tank in blankets and putting it in the tumble drier (on no heat).
If successful in removing the dodgy coating, the question is - why was it coated? Perhaps there are old leaks that need a new tank liner treatment.

[jdvorchak]

I took the tank off today and drained what looked like about 2 gallons of very old, but liquid, fuel out. Smelled more like varnish than gasoline. Maybe even diesel fuel. Don't know what it was but it's not in there anymore. Disassembled the petcock and it's soaking in white vinegar now. I'll leave it over night. So while just messing around waiting for stuff to either soak or dry I cleaned up the fuel tank. To my surprise there is pretty nice paint for 33 year old bike. Took a little window cleaner and followed it up with spray polish and I think it cleaned up nicely.

[azr]

Man you haven't even polished it yet! that will polish up like the day it came off the factory floor.

[jdvorchak]

Next I'll pull the carbs and begin working on them. I have sprayed some silicon on the rubber boots and insulators. Should be slippery enough to pull the carbs tomorrow without tearing anything up. I'm pretty sure I'll find a nasty mess in the carbs. The good news is that petcock wasn't flowing a drop so maybe it kept what was in the tank out of the carbs. I may try to run it using an aux tank I have for doing carb sync before I pull the air box off.