Can anyone help with some advice ?

I have a 1975 70hp Johnson, would it be ok to bore all three cylinders to .30 over with no affect to the engine as to changing the carbs or any other parts ?

displacement of engine will increase,theoretically it will need a hair more fuel in there,Running lean is dangerous for engine,I am not sure of proper course of action,but i would surmise bigger fuel jets.Wait for the big guns to chime in

No need to change anything.

No need to change jets etc.... you're perfectly safe reusing the original components. Done that hundreds of times with no comebacks.

With the E10 fuel anything bored .030 and bigger need to go up a size. I up all my customers jets when rebuilt....

To each his own. JMO.

When was "E10" first introduced and used?

E10 also called gasahol fuels appeared in the early 80"s and many service bulletins was issued not to use it in 2 stroke engines....as the "green" agenda advanced it has been phased in where no lead is now rarely found. Beware E15 is coming by government mandate...

faztbullet said:

E10 fuels appeared in the early 80"s and many service bulletins was issued not to use it in 2 stroke engines, as the "green" agenda advanced it has been phased in where no lead is now rarely found. Beware E15 is coming by government mandate...

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I appreciate the speedy reply, thank you. Your forwarded information indicates that since I retired in 1991, I was faced with this E10 situation for approximately 10 years. Ten years of which not one shred of information pertaining to this crossed my desk... and back then I was pretty demanding in reading every word of bulletins etc, taking them quite seriously.

However, back then, there was someone hired as a service manager who knew nothing about the marine trade and was hired simply because he was a friend of the general manager, both of which who suffered the swelled head syndrome. This "service manager", I would assume received the bulletins and that's as far as they got. Apparently I retired at a proper time.

Most small engine manufactures recommend staying away from E10 if at all possible. I work on 2 stroke yard equipment as a hobby, which leads all my friends to me when they won't run. 95% of the problems I see is caused by E10. Stay away from using it if at all possible.

Dont get me wrong as Mercury states E10 is a really good fuel but.....engineering was done to allow for its use such as compression reliefs,lower compression,timing specs,material changes,etc.