Re: how much rust is too much for inside your gas tank?
If you use WD-40 get a rust fuel proventitive to rince through it afterwards. It will mix badly with hot water and will never fully leave the tank and leave pockets of water and WD-40 in the tank. WD-40 was made in the 50's for use with missiles and rockets ready for the war. The name WD-40 came from the product itself. Water displacement #40 (because their first 39 attempts failed) and the main ingredient is fish oil. Have a look on the web what CAN happen when fish oil and water in small amounts mixed with 2 stroke oil and fuel can do to a bike. Fish oil wont dilute with petrol and sits on top so if you run your tank dry it can be all your engine will get. Had dramas with my yamaha yz80 from doing the same thing. Sorry for the trivia lol. Bdu