Fuel/oil mixture ratio for 31cc weed wacker?

What fuel/oil mixture ratio should i use for my 31cc Ryobi weed wackers?

At the moment i have been using 40:1. Is that ok?

Yeh dude from what i've read about current 2 stroke oils 40:1 sounds fine, Some guy's here use the opti 2 oil at 100:1!

100:1!!, that must be some pretty damn good oil!!

yeh i dunno but im sure its good stuff, i cannot find it here anywhere yet. I have mates with gokarts and they use a synthetic Oil (Motul) At 20:1 ? my bike runs crap on it

Just did a lil search and cannot find any retailer or a distributor that sells opti 2 in australia.
I did find this. 48 x 1.8oz pouches $160 aud
NEW BRIGGS 1.8OZ 2-CYCLE OPTI OIL 20096DIB - eBay, Other, Yard, Garden Outdoor Living, Home Garden. (end time 09-Oct-09 06:35:01 AEDST)

It does really depend on the oil. 40:1 is fine with many oils.

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stihl dealers in victoria carry opti-2 - mebbe worth a try in NSW...
but you're right, it's hard to track the stuff down in aus.

I am using Castrol 2T Self Mix 2 Stroke Oil. Is this good enough quality?

There is a stihl dealer like 4km away from my house. But i think the oil i have now is good enough.

Yeah i also use Motul synthetic oil in my motorbike and go-kart. Motul is by far the best i have used. Before i started using Motul i was using shell in my motorbike and it kept fouling my spark plugs.