Type of gas to use for 1974 XS650

[Jakethesnake1994]

Hey guys,

Just a quick question for you, I bought a 1974 XS650 and I’m wondering if the 94 octane gas is safe to use?

I overheard someone saying that the 94 burns hotter then the 87 or 89 octane and it might blow the engine?

What do you guys think?

Cheers,

Jake

 

[rsor]

I believe that these motors call for higher octane fuel like that. I use 94 octane, and they run a lot better than any octane less than that. We are lucky here in Canada to find that I think, Around here you can only get that 94 octane at certain Petro Canada stations.

 

[Mailman]

I run mid grade gas in both of my 650’s no problemo.

 

[Kevin Werner]

All, please remember, an octane rating indicates the fuels resistance to compression combustion (detonation). Octane, 8 carbons- and heptane, 7 carbons, have the (virtually) same BTU per CC.
IIRC longer carbon chains resist detonation. In the old days it was easy for refineries to produce a lot of gasoline with lots of 7 carbon chain mixtures, heptane. There was a more expensive or difficult or longer process to produce octane (8 carbon chain fuels). Military and/or aviation engines with superchargers and the resultant higher combustion pressures suffered detonation problems with low octane fuels. Understandably this was in the Model A/ Ford flathead era when compression ratios for the transportation sector was 6.5:1 and octane ratings did not matter much EXCEPT for supercharged radial engined aircraft.

 

[Mailman]

All, please remember, an octane rating indicates the fuels resistance to compression combustion (detonation). Octane, 8 carbons- and heptane, 7 carbons, have the (virtually) same BTU per CC.

Yeah that’s always been my understanding, if you are not having a pre ignition problem , there’s really no benefit to higher octane ratings. My bikes don’t ping.

 

[Kevin Werner]

One advantage of higher octane fuels IN MY AREA is that they have no ethanol added. I believe my carbs have modern gaskets, seals and o rings, but, why take a chance when I will run a 1000 or so miles a year.

 

[JesseeS]

These bikes are hardly top tier performance machines. They are reliable tanks. You won't find a lot of these engines blowing, and surely not from fuel choice. Hit any button besides diesel and fillerup.

 

[grizld1]

If you've bought a few nonrunning XS650 parts bikes you'll have seen plenty of holed pistons, usually due to mistimed breaker point ignition or defective advance governor, though I have seen exactly one TCI model with a holed piston over the years. Holed pistons are caused by detonation, and high octane fuel inhibits detonation by slowing flame travel; it's cheap insurance. (The cheapest insurance, of course, is preventive maintenance.) Also, premium (high octane) gas tends to stay good longer than 87 octane.

 

[Jan_P]

One advantage of higher octane fuels IN MY AREA is that they have no ethanol added. I believe my carbs have modern gaskets, seals and o rings, but, why take a chance when I will run a 1000 or so miles a year.

That is what I am thinking also If I could I would buy without ethanol .. What do the higher ups care if old vehicles are getting scrapped.

 

[grizld1]

BTW a higher octane rating doesn't mean that the fuel produces higher energy; it means that the fuel produces slower flame travel than fuel with a lower octane rating. Years ago, AMA rules allowed 45 ci (750 cc.) flat head engines to race against 30.5 ci. (500 cc.) OHV engines in the Expert class. Team Harley ran the lowest octane fuel they could find as race gas. One performance factor with flat head motors was getting flame travel fast enough.

 

[bosco659]

I’ve always used 92 octane and better in my bikes and all small engines. One of the main reasons for buying this grade of fuel, is they are ethanol free. My small engines like weed whacker, chainsaw and 2 stroke lawnmower perform well with the higher octane and the “shelf life” of the fuel is better - perhaps due to the absence of ethanol. Sure it’s costs quite a bit more, but with the low volume I buy in a year, the peace of mind it buys me is worth it. If it was for my daily driver that I’d fill up every week or so, the increased visit would hurt. Cheaper 87 octane “regular” fuel for my 4Runner.

 

[REPETE]

I run 89 octane non-ethanol which is available at numerous gas stations here in Florida. Apparently it's widely used by boaters, which we have a lot of.
Before sticking with the non-ethanol I... like many others... believed the higher the octane the better. I've noticed absolutely no difference in performance between the higher octane and the mid-range 89 octane non-ethanol.

 

[grizld1]

Alcohol free gas was made available in my area for two or three years but disappeared in 2020. Years ago Rex Blanchard (bluebikerblan) recommended marine formula Stabil as an additive with high octane gas if 10% ethanol was your only available fuel. I've followed that advice, and my chain saws and brush cutter haven't complained.

 

[bosco659]

Alcohol free gas was made available in my area for two or three years but disappeared in 2020. Years ago Rex Blanchard (bluebikerblan) recommended marine formula Stabil as an additive with high octane gas if 10% ethanol was your only available fuel. I've followed that advice, and my chain saws and brush cutter haven't complained.

Yes I use Stabil too (too cheap to buy the marine grade though lol). I know it may be a waste of money if I have ethanol free fuel, but places like the cottage where I may buy 5 gallons of fuel for the season, I still add stabilizer to the fuel. Does it do any good? Not 100% sure but I never have any fuel related issues (knock on wood) on my power equipment. For winter storage of cars I fill the tank with ethanol free fuel and a 4X dose of stabilizer. Again, is it necessary? Not proven but keeps me happy.

 

[jetmechmarty]

Option #1 for me is E0, or no ethanol. It's easy to find 87 octane E0 around here. E0 is harder to find in other octanes. When I have to use alcohol fuel, I opt for 93 octane.

 

[Jim]

BTW a higher octane rating doesn't mean that the fuel produces higher energy; it means that the fuel produces slower flame travel than fuel with a lower octane rating.

Exactly right. The higher octane content fuel burns slower... the flame front. This helps keep combustion pressure more even and progressive. A faster front speed means combustion pressure builds more rapidly. Add a little more spark advance in the mix... starting the flame front early... and we get detonation. Higher octane is good insurance, but as Dick says... good preventative maintenance is cheaper. I do both.

I can get ethanol free 93 octane here. That's the only ethanol free blend available. I can let my bike, mower, etc sit all winter with fuel in the bowls and they'll run just fine in the spring. You know... just like they did in the old pre-ethanol days.

 

[5twins]

I've never put Stabil in my bikes. Stored through one winter in my unheated garage has never given me any issues. I do, however, have to use it when storing my snowblower through the hot summer. I didn't one year and it gave me starting issues that next winter. The gas apparently went bad and I had to drain and replace it.

 

[Adamc]

All, please remember, an octane rating indicates the fuels resistance to compression combustion (detonation). Octane, 8 carbons- and heptane, 7 carbons, have the (virtually) same BTU per CC.
IIRC longer carbon chains resist detonation. In the old days it was easy for refineries to produce a lot of gasoline with lots of 7 carbon chain mixtures, heptane. There was a more expensive or difficult or longer process to produce octane (8 carbon chain fuels). Military and/or aviation engines with superchargers and the resultant higher combustion pressures suffered detonation problems with low octane fuels. Understandably this was in the Model A/ Ford flathead era when compression ratios for the transportation sector was 6.5:1 and octane ratings did not matter much EXCEPT for supercharged radial engined aircraft.

Blimey TW did you get a chemistry set for Christmas. Impressive.

 

[Kevin Werner]

Blimey TW did you get a chemistry set for Christmas. Impressive.

While I did work in R&D in the labs at a plastcs compounding company for 6 years the Octane/Heptane knowledge came from technical articles in Cycle World or Cycle Guide or Motorcyclist in the 70s and 80s. Kevin Cameron IIRC was a pretty good technical writer that I remember, but I am sure there were others, and he did a quite informative article on prewar aviation engine development and failures related to octane rating. In R&D you end up looking at all the little details when you are trying to improve a product or reduce it's cost. If I spout off about a MSDS (material safety data sheet) it is because I learned to look at those, sometimes with a jaundiced eye. Most of my chemistry sucks, I did a lot of process development, method development and sample prep and testing.

 

[Adamc]

While I did work in R&D in the labs at a plastcs compounding company for 6 years the Octane/Heptane knowledge came from technical articles in Cycle World or Cycle Guide or Motorcyclist in the 70s and 80s. Kevin Cameron IIRC was a pretty good technical writer that I remember, but I am sure there were others, and he did a quite informative article on prewar aviation engine development and failures related to octane rating. In R&D you end up looking at all the little details when you are trying to improve a product or reduce it's cost. If I spout off about a MSDS (material safety data sheet) it is because I learned to look at those, sometimes with a jaundiced eye. Most of my chemistry sucks, I did a lot of process development, method development and sample prep and testing.

Well that explains your knowledge. It's great you could recall the learning and share with us here. I'm still impressed!