Originally Posted by Fenlander
Disschord looking back at my post and the following ones I want to make sure we're not misleading you with mention of 100:1.
I believe it's unlikely your outboard would be a 100:1 model unless you find an original sticker on it or had its instruction book from new that said so.
So go with 50:1 to avoid any damage.
Even if you found concrete evidence that it was designed for 100:1 as it's looking to be over 30yrs old consider this... Max and I have the same outboard as each other (mid 2000s Mercury 15hp) and ours were designed for 100:1 with the engines clearly stickered and/or the information in their manuals. Even so we choose to use the halfway (between leisure and commercial use mixes) 75:1 mix for extra protection.
Many thanks everyone I will go with 50/1 as I would rather my engine didn't sieze.
Your also so helpful thankyou