froot - 18-2-2007 at 08:56
My dilemma: I have a translucent plastic fuel tank for a 2stroke engine that has been standing with mixed fuel in it for some time. Now I have noticed
some 'sediment' that has settled in the draining sump of the tank and wish to clean it. I then noticed that the copper suction tube which descends
directly above the draining sump is covered in a green mass. The sediment turns out to be a dirty oily liquid that's immiscible with the fuel. I am
becoming very suspicious of certain 2-stroke oils.
Feel free to have a stab at the chemistry of this mess and I would appreciate any recommendations on how to clean it up properly.
ps, I can't get my hand inside so scrubbing is not an option. 
12AX7 - 18-2-2007 at 12:51
Oh...hmm well, KMnO4 and a bit of acid to kick it along?
Maybe not. 
Surely you've tried solvents already, things ranging from alcohol to alkane to ethers and such?
Tim
Rosco Bodine - 18-2-2007 at 14:06
Xylene knocks the crap out of engine sludge , valve crud , and fuel deposits better than anything I have seen .
For an aerosol , throttle body cleaner ....
and for a fuel additive ...Methanol and/or Chevron Techroline injector cleaner .
On a 2 stroke you want to use a fuel stabilizer or
a 2 stroke oil that already contains it ...and drain
any unused fuel , then run the thing dry before storage .
If it gums up anyway ....try to clean it out with straight methanol , use ether starting fluid to save a lot of rope
pulling and blisters , leave the choke open after a shot
of ether , fire it off and gradually close the choke to
keep it running a few seconds and get the fresh fuel flowing . Usually the problems are bad fuel lines ,
plugged filter screens , gummed jets , bad fuel pump
diaphragm , or a dirty , wet , or fouled plug , or flooded
engine which can be from a dirty air filter .
If it is a metal based corrosion in a location where you
can hose it off , the hydrochloric acid 10% toilet bowl
cleaning liquid gels or a spray on NaOH based oven cleaner ....along with a bit of wire brushing or an old toothbrush should get the crud off right
down to the metal . Best to neutralize and rinse throughly afterwards
or otherwise you can set up or aggravate corrosion problems .
Levi - 18-2-2007 at 14:17
The green sludge is copper carbonate, you can neutralize it will hydrochloric acid to make it soluble and then wash it away with water. The copper
tube will be unaffected by HCl unless you mix it with a strong oxidizer also. You should rinse away any excess fuel/oil before you try the acid
treatment to avoid any reaction.
froot - 19-2-2007 at 02:39
Thanks for the replies.
This is probably ass about face but I cleaned the carbs first. They are side draughts with the throttle actuated from above and these were stuck! The
solvents I tried were acetone and methylene chloride which had little or no effect on the residue stuck to the brass needles and jets. What I did then
would probably raise a few eyebrows, but I dipped each fitting in a glass of dilute nitric acid. As soon as it fizzed I'd immediatly place them under
running water and only stop when that metallic acidic taste was no more. They came out spotless, cleaner than you can buy them! This is a once off
quick clean, not to be done again on the same parts.
I havn't tried ether because that bottle of ether in my garage hasn't been opened in a couple of years and this makes me a bit nervous, but being
recommended I'll give it a try. It hasn't been contaminated or in contact with much oxygen at all so, yes, maybe safe to open. I'll definitely give
xylene a bash as well.
Rosco Bodine - 20-2-2007 at 10:25
Yeah definitely try xylene . After you try it one time ,
especially on those stubborn gummy carbonized
sludge like deposits under valve covers on 4-strokes ,
or combustion / exhaust deposits on 2-strokes .....
you won't ever be without it for cutting oil based varnishes . You have to brush it on and let it soak ,
maybe even make more than one pass . But it will work
where nothing else works at all .
Straight methanol works better on fuel based varnishes ,
and its solvent action is virtually instantaneous . It is way better than acetone or methylene chloride .
I always look at the contents for aerosol throttle body cleaners for both xylene and methanol , and if they aren't in it ....don't buy it .