What precautions need to be taken before welding on a fuel tank. I want to modify my tank for fuel injection, it has been empty for about 12 months would a good wash with hot water and detergent be enough?

degreaser takes the residue out, but its mainly vapours that are your problem. If you can still smell fuel, flush it some more.
Ive cut and welded a few, and no eplosions as yet!

Yes,

its the fumes that are dangerous....

I have heard of people filling the tank with water
before welding...
then No fumes...

Lee

fill with water when you can i have even when i sure it enpty i stick a oxy torch in just to kake sure i had a very good friend get really badly burnt from a empty tank he will never be the same so when you are sure its empty flame it BE SURE

Filling with water is the best idea. Also helps you see any pinprick holes or blow-throughs you've made with the welder.

This reminded me of an old story/myth............
A guy was told to use a vacum cleaner when welding a fuel tank, however he inserted the vacum hose instead of the blower nozzle
................................................ahh well, let's try again!!!!

my mates misfortune was not an explosion but while he was welding a small hole blew through making a flame througher out of the tank a big hole would have went bang scaring the s../'t out of him the welding had aused the fumes to be under pressure and he was face to face with a flamethrougher
and he had it upside down so the fumes tryed to get out the bottom

[ Edited on 18-5-2007 by greedy53 ]

[ Edited on 18-5-2007 by greedy53 ]

if it goes bang ,you didn't wash it out enough.
hold your breath and cross your fingers before starting.
it always works for me,although there was this one time at band camp,but thats another story.