If it's running premix , just close the petcock and top off the tank , tighten the cap in place .
If straight gas , add oil and do the same as with premix .
If you want to get rid of some rust :
( I should just boiler plate this )
I rec'd my order of wood bleach ( Oxalic Acid ) and thought it best to test it before I subjected my fuel tank for rust removal .
I mixed a rather mild solution for the test . Here are some before and after pics :
The parts looked almost this good after just a couple of hours bath , but I left them in over night to see if the deep reaches would be 'taken care of ' . The pulley was totally rusted .
I pulled the parts and rinsed them in a bath of hot water , then let them dry . The Oxalic acid seems to eat rust and leave a protective coating . I wiped some of that coating off the rear brake plate . Also note that the acid does not effect painted parts ( a big plus ) .
This was an experiment for me . My Simplex had a bit of rust forming in the gas tank . Not too bad considering the bike is 55 years old . I'd read that different acids worked for removing rust .
I used muriatic acid to clean my XT350 tank with decent results . That tank did flash rust and I retreated it and then neutralized the acid ASAP . It still formed a small amount of flash rust . I'm running it with an in line paper fuel filter and haven't had any problems .
The Simplex tank is a bit more rare and harder to find . I was reluctant to use muriatic acid in it for those reasons . Through research , I read about oxalic acid , sold as wood bleach . Oxalic acid is a lot safer to work with , but still requires due caution ( READ THE LABEL ) . It's not nearly as toxic as muriatic acid . It does NOT harm painted surfaces . It just eats rust and leaves a protective coating on the steel after being thoroughly rinsed with water .
I used a diluted mixture from what is suggested , which is 12 ounces to 1 gallon of water . I used 12 ounces to 2 gallons of water . Being as the solution was weaker , I left the mixture in the tank twice as long and the results are shown below .
This is what I used :
Here's the rusted tank :
And, here's the tank after being filled with oxalic acid for a couple of days :
This stuff really does work great .