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Hey Tom,
It's been a long time since I rebuilt my 81 in 2000. I rode it in essentially OEM configuration from '83 to 92, some estimated 50k miles...estimated because my actual odometer broke at ~970 miles, just used the tripometer for fuel fillups. I remember reading it requiring 92 octane, and therefore used Premium. I grew up when octanes were 100+ before they took the lead out. I didn't realize that they had recalculated how they determined the octane levels.
When I rebuilt my bike in 2000 after a 8 year corrosive nap outdoors
, I put in new pistons due to rust exposure of the cylinders, and this site wasn't up and running then so I didn't know that I possibly could have reconditioned the cylinders instead of boring it out. But I did, putting in the 1179cc kit. And since it was supposed to boost the compression to around 10.5:1 I opted to continue running premium for fear of burning holes in my new pistons. My valves were in decent shape, only required a lapping to get them to seal well, and just installed new oil seals with the head work. I vaguely remember using a wire brush on a drill to scrub off some of the carbon from the valve shafts...but it didn't seem like there was much there.
I have just recently dropped my fuel choice down to the medium grade. Part of my concerns were that with both the slightly louder exhausts, and full face helmet, earplugs, that it would be difficult for me to be able to hear the pinging of preignition/knocking. I've been told that unless I was running compressions in the 11+ range, that higher octanes are needed to prevent preignition/knocking. I may eventually go to regular, but will have to ensure that I run it locally WITHOUT earplugs so that I can check/listen to make sure I'm not hearing any pinging before I can feel confident in continuing to run the regular stuff!
Octane S-L-O-W-S down the speed that the fuel burns, so helps keep a single flame front explosion wave that pushes the piston down evenly. Too low octane causes the fuel/air mixture to ignite in more than one location within the combustion chamber due to a variety of factors...but this creates multiple flame fronts that then push down on the piston in different places which can cause it to rock/knock side to side.
Oil is going to burn slower that gasoline, and so I would expect putting MMO in the fuel would increase the octane, not lower it. Too low of octane is more likely to "blow" your engine with preignition, and possibly burning holes in pistons compared to premium.
I'm not too worried about the affects of E-10, but if I were to get 100 % pure gasoline, I wouldn't worry too much about it being premium. And IF you have updated your ignition with newer coils, then you're getting a much stronger spark than the early 78-80 1.5 ohm coils ever could provide. And if you run the bike in the lower rpms, then you're giving it more time per cycle to burn more completely than if you are running in the 7k range.
T.C.
It's been a long time since I rebuilt my 81 in 2000. I rode it in essentially OEM configuration from '83 to 92, some estimated 50k miles...estimated because my actual odometer broke at ~970 miles, just used the tripometer for fuel fillups. I remember reading it requiring 92 octane, and therefore used Premium. I grew up when octanes were 100+ before they took the lead out. I didn't realize that they had recalculated how they determined the octane levels.
When I rebuilt my bike in 2000 after a 8 year corrosive nap outdoors
, I put in new pistons due to rust exposure of the cylinders, and this site wasn't up and running then so I didn't know that I possibly could have reconditioned the cylinders instead of boring it out. But I did, putting in the 1179cc kit. And since it was supposed to boost the compression to around 10.5:1 I opted to continue running premium for fear of burning holes in my new pistons. My valves were in decent shape, only required a lapping to get them to seal well, and just installed new oil seals with the head work. I vaguely remember using a wire brush on a drill to scrub off some of the carbon from the valve shafts...but it didn't seem like there was much there. I have just recently dropped my fuel choice down to the medium grade. Part of my concerns were that with both the slightly louder exhausts, and full face helmet, earplugs, that it would be difficult for me to be able to hear the pinging of preignition/knocking. I've been told that unless I was running compressions in the 11+ range, that higher octanes are needed to prevent preignition/knocking. I may eventually go to regular, but will have to ensure that I run it locally WITHOUT earplugs so that I can check/listen to make sure I'm not hearing any pinging before I can feel confident in continuing to run the regular stuff!
Octane S-L-O-W-S down the speed that the fuel burns, so helps keep a single flame front explosion wave that pushes the piston down evenly. Too low octane causes the fuel/air mixture to ignite in more than one location within the combustion chamber due to a variety of factors...but this creates multiple flame fronts that then push down on the piston in different places which can cause it to rock/knock side to side.
Oil is going to burn slower that gasoline, and so I would expect putting MMO in the fuel would increase the octane, not lower it. Too low of octane is more likely to "blow" your engine with preignition, and possibly burning holes in pistons compared to premium.
I'm not too worried about the affects of E-10, but if I were to get 100 % pure gasoline, I wouldn't worry too much about it being premium. And IF you have updated your ignition with newer coils, then you're getting a much stronger spark than the early 78-80 1.5 ohm coils ever could provide. And if you run the bike in the lower rpms, then you're giving it more time per cycle to burn more completely than if you are running in the 7k range.
T.C.
.
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