Octane?

samc

New Member
Joined
Jul 29, 2025
Total Posts
3
Total likes
0
Location
Pacific northwest
According to my shop manual (published approx 1968), the technical data for 250 and 350 bikes states the required fuel needs to be above octane 95 which is higher than even premium sold in my area. Just wondering if the way octane is measured in the last 50 years has changed or what?
 
I always run E5 fuel in my petrol engines, ranges from 97 to 99 octane.

For the bikes, it's the reduced ( or even zero ) ethanol content that I go for. The CB600 engine has a 12 to 1 compression ratio, so might benefit from the higher octane, although in practice I can't tell the difference from E10 fuel. My car has a 13.1 compression ratio ( 2.5 litre Ford hybrid ) and an ECU that I assume can adjust itself to make best use of higher octane fuel.

Also, the posh petrol allegedly has more additives in it, said to keep things squeaky clean inside. Didn't work with my previous diesel engine though, using Shell V Power diesel.
 
I hadn't thought about octane ratings for these old bikes. I would have just filled it with 87 and went on my way. If you rebuilt your carbs with those "ultimate" kits, would gas like E10 be as much of a problem?
 
sp00xe said:
I hadn't thought about octane ratings for these old bikes. I would have just filled it with 87 and went on my way. If you rebuilt your carbs with those "ultimate" kits, would gas like E10 be as much of a problem?
Click to expand...
87 octane is fine for your bike, but the only issue with E10 is if you leave it sit in the tank too long. If you can't find any fuel without ethanol, you'll have to use a little Stabil in your fuel to help with the ethanol. Hopefully you'll ride it semi-regularly and that won't be a problem, but if you let it sit for an extended time you should add more Stabil to the tank, shut the fuel off and drain the float bowls.
 
ancientdad said:
87 octane is fine for your bike, but the only issue with E10 is if you leave it sit in the tank too long. If you can't find any fuel without ethanol, you'll have to use a little Stabil in your fuel to help with the ethanol. Hopefully you'll ride it semi-regularly and that won't be a problem, but if you let it sit for an extended time you should add more Stabil to the tank, shut the fuel off and drain the float bowls.
Click to expand...
Ah, good advice thank you. Once it's running I plan on riding it probably almost every day, if not every day. I'd probably still put Stabil in it anyway however.
 
ancientdad said:
87 octane is fine for your bike, but the only issue with E10 is if you leave it sit in the tank too long. If you can't find any fuel without ethanol, you'll have to use a little Stabil in your fuel to help with the ethanol. Hopefully you'll ride it semi-regularly and that won't be a problem, but if you let it sit for an extended time you should add more Stabil to the tank, shut the fuel off and drain the float bowls.
Click to expand...

sp00xe said:
Ah, good advice thank you. Once it's running I plan on riding it probably almost every day, if not every day. I'd probably still put Stabil in it anyway however.
Click to expand...

I keep a few 5 gallon cans of ethanol free fuel around for bikes and power equipment, and always add a stabilizer (StarTron) since sometimes it gets used quickly, and other times it can sit for months before I use it all. It seems pricey, but the dosage is like one ounce for 5 gallons.
 
esh21167 said:
I keep a few 5 gallon cans of ethanol free fuel around for bikes and power equipment, and always add a stabilizer (StarTron) since sometimes it gets used quickly, and other times it can sit for months before I use it all. It seems pricey, but the dosage is like one ounce for 5 gallons.
Click to expand...
Yeah, and good non-ethanol fuel with some additive will last as long as 6 to 9 months IME, maybe even longer. With the hurricane activity we had last October, I ended up with about 7 gallons of 90 octane non-ethanol and I still have some of it left. The pressure washer, garden tractor and walk-behind mower don't care at all how old it is and it still runs fine in my 450 too.
 
In the UK don't buy E10 that's the regular unleaded, this is harmful even to new vehicles, hence many new vehicles having recalled from the dealership.
Only use E5 super unleaded if it is available, this has a maximum of 5% ethanol but in a lot of cases can contain zero ethanol, this is the one to use always.

You can also use a fuel stabiliser called Ethanolmate, we sell it here

Ethanolmate: ETHANOLMATE - Protect against the corrosive effects of fuel containing ethanol! (250ml) for Classic & Vintage Cars | Vintage Supplies | Vintage Car Parts

ETHANOLMATE is the leading product for use with ethanol-containing petrol - E10 and E5. Designed as a corrosion inhibitor, fuel stability improver and
www.vintagecarparts.co.uk www.vintagecarparts.co.uk

All the best
Warren
www.vintagecarparts.co.uk
 
Last edited by a moderator:
You must log in or register to reply here.
Back
Top Bottom