Octane

[XS1100_OEM4ME]

I have seen a few post on here about holes in pistons and bike's running hot and so on. 1st, if the carbs are lean, that is the #1 prob IMHO. A cheap insurance though is to run high Octane fuel, the higher the Octane the cooler the motor runs and less pre ign. Both cause motor failure over time. It also can help with the burnt and dropped valve's JIMHO, it is your bike and your $$$

[bikerphil]

I run low test and today riding the SF, I had to goose it in 2nd to get out of the way of a cage and guess what, ping...ping...ping. I think it is due to carbon build up and running the timing slightly advanced.

[natemoen]

But higher octane fuel (when not needed) also helps contribute to carbon buildup.

[XS1100_OEM4ME]

?????

But higher octane fuel (when not needed) also helps contribute to carbon buildup.

??????, never heard that one, High Octane fuels have more cleaning and and build-up reduction adidtives then cheap low octane fuels, JIMHO

[bikerphil]

Well I'm gonna put super in tomorrow and see if that helps, I don't like that ping sound but I do like the static timing advanced a little bit, the bike is much more peppier off the line that way.

[crazy steve]

Running higher-than-needed octane fuel is a double-edged sword. Yes, it can reduce engine temps and pre-ignition. But if you're having issues with pre-ignition on these motors, that simply masks the problem, it doesn't fix it.

Generally, pre-ignition won't burn holes in pistons; it can fracture the piston tops and/or destroy the ring lands from the shock (also bad for rod/main bearings), but won't reach the temps needed to melt stuff as a rule. You'll usually break something before melting anything.

All grades of gasoline burn at roughly the same temp; the difference is the rate of burn, with higher octanes burning slower. Any of these motors in proper tune and good, OEM mechanical condition will run on most regular fuels, although depending on your local/brand 'blends' you may need a mid-grade in some cases. Running a higher-than-needed octane can reduce mileage, and will definitely promote carbon build-up in the combustion chamber and on the valves. Get enough carbon build-up and you'll have to run high octane, but you may get to the point where even premium won't be high enough.

Another point is these motors aren't low-speed torque monsters. If you're getting knocking below 3K rpm, you're in too high a gear. They're not V-twins, with big torque off-idle; you need to get some rpms.

[XS1100_OEM4ME]

Compression

the compression ratio on most of these is 9.2 to 1. Today's fuel has changed and most car's with a 9 to1 or higher compression ratio recomend or "require" higher octane My bike has 4 pistons, no holes, no dropped valves and no bad carbon on plugs, I run super or primium, must just be luck

[Bonz]

This has been batted around in more threads/posts than i can remember, and the collective says a resounding "use the lowest octane you can that keeps the ping at bay".

Unless it is just an old wives tale/urban legend that too much octane when not needed carbons up exhaust valves... Or if it feels better to fill up with more expensive fuel than needed, then that works too.

If it pings, go up a grade by all means. Otherwise i don't see the point.

[XS1100_OEM4ME]

Ping

This has been batted around in more threads/posts than i can remember, and the collective says a resounding "use the lowest octane you can that keeps the ping at bay".

Unless it is just an old wives tale/urban legend that too much octane when not needed carbons up exhaust valves... Or if it feels better to fill up with more expensive fuel than needed, then that works too.

If it pings, go up a grade by all means. Otherwise i don't see the point.

Ping is only "ONE" indacator, many motors melt the pistons without "ping" as is clear from so many members having holes in their pistons, most never mentioned "ping" Ping will crush bearings and warp valves till they drop. Learned this crap the hard way in my drag racing days. Heat is the big deal, it is most likely from lean mix, but add that to, too hot low octane gas and, well it's your motor, and what do the manufacturer's know anyway

[crazy steve]

the compression ratio on most of these is 9.2 to 1. Today's fuel has changed and most car's with a 9 to1 or higher compression ratio recomend or "require" higher octane

The '78-79 bikes had a 9.2:1 ratio, the later bikes dropped to 9:1. But even the '78 (the higher compression and more static timing than the later bikes) runs fine on 'regular' fuel as long as the pump octane is 87 or more. 86 octane may be marginal, 85 definitely is. 'Back in the day', 9.5:1 or less was a 'regular' fuel motor, you only needed premium if you got over 10:1. Again, some local/brand blends may not be up to the task, so YMMV.

Even today, 9:1 is nearly always a 'regular' motor. Yes, with all the electronic controls sometimes you can see a power/mileage increase on a given vehicle, what with knock sensors and continually adjusted timing and mixture. But the reverse is also true; there's motors out there with 10:1 ratios that are rated for regular. Even my new Mustang GT will run on regular, and that's with a 11.5:1 compression ratio! You take a 20hp hit on power (supposedly), but otherwise I can't tell (I do run premium though.. ).

[XS1100_OEM4ME]

My bike

My bike didn't come with "ping' sencers, or vanos timming adjust, or an on board computer to adjust timming to fuel raito. It is just an old dog from a day gone by when all fuel had lead in it to cushin valves and quiet pinging and cool parts, just an old dog that can't learn new tricks, but no holes in my piston's and no dropped valves on prem gas, just lucky I guess, me and my old dog, just lucky

[TADracer]

Running higher-than-needed octane fuel is a double-edged sword. Yes, it can reduce engine temps and pre-ignition. But if you're having issues with pre-ignition on these motors, that simply masks the problem, it doesn't fix it.

Plus 1 on this.

Its not just fuel grade or timing or plugs or compression ratio. It is all these and a host of other things. You must find a balance of all these things and more. Alot has to do with the combustion chamber temp. Get that in the 1,200 degree range and your pinging will most likely go away. There is the rub. Finding that sweet spot is not always easy.

JMHO, Reducing engine temp is not always the ticket. All I can speak of is my experience. My 79SF has a bit of head work, some cam timing, 4-1 header, pods and some of the other things we all seem to reach for. I had a pinging and carbon problem and after a bunch of tinkering I found that my particular motor likes one heat range hotter on the plugs. A switch to NGK BP5ES plugs did the trick. No pings and regular octane works great.

[bikerphil]

Update: Put some mid grade 89 in there, no ping anymore.

[Bonz]

Good info, guys. Glad the 89 octane did the trick. You are at the low of the low when it comes to elevation for sure!

Here in Colorado (5000-7000+ feet elevation) 85 octane does the trick very nicely in my 80SG and 2001 ZRX 1200. Plugs are nice tan color, engines run spot on even in the hottest temps of summer (100 deg). Of course, the elevation allows the lower octane. But again, I run what the bike dicates. And I run 107.5 mains in the carbs with the high elevation as well.

I didn't make mention of holes in pistons, rather exhaust valve carbon was my point in running higher octane than needed or specified.

It was said "so many members having holes in their pistons". I searched past threads and found one holey piston thread from yesterday, attributed to lean mixutre and then couldn't find anything more recent than middle of last year, and each time it was a lean condition/heat.

When race cars burn a piston, they are running too lean/too hot, and the grade of gas is a known quantity in those cases with the engines tuned around the gas, per se.

Would it be correct to say that when an engine is tuned too lean, it runs hot, and then (more or less) no octane rating is going to save that motor (pistons), as any gas would be asked to do something outside the scope of what gas is supposed to do.

[motoman]

Hmmmm........wonder how many of those bikes showing lean cond. or worse, ventilated pistons are also "upgraded" to hotter coils and Irid. plugs. Definitely something if thrown in the mix that's gonna affect burn rate and temps. Basicly why I've stayed with the stock secondary ignition system even though it is on the 'wimpy' side by todays standards. These motors were already a lean burn motor by design, in order to better meet emmission regulations. IMO, any ignition improvements would likely warrant a bit richened up mixture, especially the main circuit if majority of bikes time running is spent on the 'slab' at a constant, steady higher RPM.