Best fuel for small Two Stroke

[The Complete Angler]

Hi All

I purchased a small boat a year ago now which has a 2004 Yamaha 30hp two stroke that has always run great. I buy the best, Yamaha branded oil for it but have only put 91 unleaded fuel in. It got me think, should I be putting premium 98 or 95 in it?
I’ve been doing some research and some say absolutely, you should be running premium and some say no, you shouldn’t. I don’t have the manufacturers booklet but wanted to know if anyone else has any insight and knowledge on this at all? I would’ve thought that 98 would be better and cleaner but don’t want to have it pinging or running poorly. Cheers

[gazza2006au]

Just my two bob i run 91 in everything excep the closes garage only has 91 E10 next is 95 premium i very rarely buy 98

You engine is a really old design that goes back to the late 1970's believe it, they have been changed just ever so slightly over the years

I had a 79 mariner 30hp (yamaha rebadge) and i had a 2005 25hp yamaha there ver the very very minor differences in block castings but basically the same engine, i tried swapping my powerhead base plates the yamaha fit the mariner but the mariner didnt fit the yamaha the yamaha was a bit more beefed but i cant recall the problem i had was a couple of years ago

So pretty much the engine is a 1970's design back than im not sure if we even had premium 98?

Sent from my SM-G900I using Ausfish mobile app

[stevej]

91 without ethanol, use 95 98 when the servo cant give you 91 without ethanol

only benefit to 95/98 is higher octane which in a performance engine with high compression ratios or lots of ignition advance
or a engine that can detect fuel octane and change engine parameters to suit

98 also has cleaning agents but there's information say yes or no to it affecting the 2 stroke oils negatively

[tunaticer]

Motor is designed for 89 octane rating.......RTM

[ranmar850]

Main advantage of premium is longer shelf life. If you have something that sits around for long periods unused,like generators or boats that aren't used a lot, premium will be better.