NPD reckon the 100+ will last a year if stored in a sealed container  .... so not a boat tank with a vent BUT  they are probly arse covering a bit . Personally  I would be happy to stick it in the (older  low- compression )car  , a bit reluctant to put it in the  boat  mostly coz ya cant walk home if it takes a dump. I would NOT put it in a 2 stroke.....not even the chainsaw 

 I only ever took a motor to the shop twice , 1st time it came back with a big sticking point a bit off straight ahead in the steering pivot ( apparently a bush just "fell" out of place ) 2nd time they cut the o ring on the oil filter housing  and it pissed oil out ..........now that was #*cking lucky coz I ran it on earmuffs before going out to sea  and saw the oil on the drive way . Now I measured the drip rate and did a bit of rifmatik  .......it would have taken 40 mins to empty the sump and in all probability I would not have noticed untill it chundered ( no low oil warning ).....so I fix my own stuff , Oh , and it came back without the seal on the motor cover ..... beats the poo logs outa me ... the cover was rattling loose so how they didnt notice it  themselves

100 oct from NPD? biofuel

If you are worried about the octane use 1/2 and refill with 100 again. Caution though. Where did you buy the fuel? I believe the mix from Gull has methanol in it and that absorbs water over time. Also I've been told outboards don't like water suspended in the fuel. 

Octane booster will help but one thing is for sure, if toy hear the engine 'pinging' that isn't a good thing. Turn around and head back.

My mate stored his boat at my place for three years, apart from using some epoxy to reattach the transducer that the sheep busted off it was all good to go. It was a Mariner 140 and had a full tank. We went waaaaay off the west coast on that boat with no problems.

Four strokes aren't as relaxed. Personally though I'd use an octane booster or syphon half the gas out and top up with 95. Outboard engines are in a pretty low state of tune compared to a car.

Any sign of misfiring or pinking then I'd head back in and change the lot

The 'zuks are tuned for 91 octane, you're throwing money away putting the better stuff in.

It takes me 4 fishing  days out to burn 25l of fuel  and I got sick of tipping it in the car if it ( 91 ) had been sitting for a while  so for 30c more a litre I mostly get 100+.If you use enough to keep the fuel flowing , so to speak then 91 is the best value. I have had personal experience with running to lower octane in a 2 stroke outboard, melts pistons instantly .....didnt even get out of the hole  ( 70 hp johnnie,   bit of a storey if ya want it )

 Compression ratios in 2 strokes are a bit difficult   as while they may have a low static comp ratio  the effective ratio goes up a lot when at  peak torque   as with the 2/ the incoming charge is precompressed in the crankcase and is blown thru the transfer ports into the combustion chamber , where as the (na ) 4/ has to suck the incoming charge in.

2/ motors dont like low octane ....like stale fuel and will munch a piston pretty much instantly the load come on , usually melting the edge of the piston adjacent to the ex port  , sometimes just the top ring land  but I have seen rings totally unsupported  as the whole side of the piston has gone .

  Smudge , I can save you a post ..... the piston was still oily everywhere except where it had actually melted.

While most modern cars will take 91  my  Toyota recommends 95  and the difference in power is very noticeable if I use 91 . I think   the knock sensors cut in and dial back timing and fuelling more than the actual fuel makes the difference . I did try a tank of 100+ but the only difference  I could see was that it used more of it.

 I have a Capri ( 3.9 rover  efi ) which due to a miscalculation on my part when dialling in the comp ratio  clatters badly on 91  better on 96 but still had to take 4deg out of the timing and it only rattled when the boot was down . So av gas or racing fuel was the go  which was a pita coz you couldnt pump it straight into the car  , so when BP ultra 100 showed up at the Cromwell garage .....nirvana,  then 100+  got local . Whole different car . 

Makes sense Mac

what are you sayin  bro  that I blither to much or that  I made some sense 

On one hand we are being told that using stale fuel  is unwise  but  then it seems that at what point should be considered stale is a pretty grey area. On one hand we are being told  (sort of ) 3 months is it , but its hard to dismiss all the above posters that have used year + old fuel with no ill effect. I think maybe  ,as mentioned above , that our outboards are relatively low stressed motors .  The fact that they can run high-ish compression ratios is  due to having efficient combustion chambers , spark plug placement , ignition control  .......all modern tech , and  I believe that manufacturers build in a bit of leeway coz they KNOW that most of us boaties  are not going to chuck out old fuel , and that if the engine did chunder  they would be 1st to get the blame ( Im thinkin USA here ).  And there are differing scenario's , like  for instance  , I dont go much more than 1/2 hour from the ramp  and probly not more than 1-2 km's  ( Pig Island for those who know Riverton ) , where as others go bloody miles offshore .

I guess  that if you use stale fuel  your stepping into the bullring  but that dont mean your going to get gored  ( but you'd keep one eye on the bull aye )

The Jonnie 70 I mentioned above  came to me in bits ,the boat shop I found it at had rebuilt and sold the motor 3 or 4 times  as it kept melting pistons ( you should have heard some of the theories put forward ) any how I had to resleeve the block , but it chundered twice  and I didnt twig  untill I did a compression test on a fresh rebuild ( the 2nd one for me ) and it had 185psi ........90 to 100 psi would have been a pass. I pulled the head off and found that a previous owner had planed about 2mm off the head ( you could easily see it by eye when place next to an unmolested head ). So I made my own head gasket out of a bit of copper sheet . By them the Mrs had been stranded twice  and was "NOT getting back in that tub with that motor on it , and I would have to get a new one ".  Now who's going to argue that . I had to go out of town ( Nelson ) to trade that motor in as every boat shop , and the engine recon shop  all knew about it .

That 70hp johnson  would have run rings around the 90hp Yamaha I replaced it with 

 Love your bottom pic ( ooh that didnt look good as I was typing it out ) Justanotherspearo. There is something about lookin out the back of the boat at full noise , flat water  , just looking at  the wake lines, propwash  and the sound ( I used to take the cover off the motor so I could hear it better )

Obviously this does not have a profound effect for some time  , depending on many variables  mentioned in previous posts. 

I guess  with the info available  we weigh things up and make our own choices as to whether we  go boating  or lawn mowing

And the NZ government  have set  alcohol content at 10% max 

Hamish 

why bother them with an email when they publish it for all to see on their website;

http://www.npd.co.nz/100plus-high-octane-petrol/" rel="nofollow - http://www.npd.co.nz/100plus-high-octane-petrol/