RE: Do 4stroke engines need to use 4stroke fuel?
Check out the manual or instruction sheet that comes with the engine. It will generally contain the fuel requirements for the engine. The fuel I use (S&W 12.5 % nitro and 20% lubricant) satisfies the requirements for both my 4 stroke and 2 stroke engines. Like RCKen, I use the same fuel for both.
DaveB