[Hillbilly Monster]

I have a 96 900M that is tuned nicely...It's runs without pinging on 91 octane non ethanol fuel sold around here...I prefer the non ethanol for stuff that may sit around......Now I notice the non ethanol in this area is 90 octane as they rate it R+M/2....The weather still sucks but any day now the bike will go out......You all think 90 octane is adequate? I don't lug the engine or ride two up ....

 

[Strega]

Your Owners Manual specifies the recommended minimum octane.

 

[duc96cr]

I think the non ethanol they sell in Florida is 89 octane and my bikes run fine on it.

 

[PhilBoncer]

87 octane (R+M)/2 is fine for these engines. The owners manual gives a higher number due to the different way they measure it in Europe.

I bought an M900 new in 1993, and ran it on 91 octane "to be safe". The first time we had the heads off, at 122K miles, there was a fair bit of carbon buildup from incomplete burning, due to running too high an octane rating. My mechanic scrubbed it all up, and told me to stop running premium -- fo to regular. So I did that, and it stayed cleaner inside for the next 140K.

So, just run regular 87 (or the lowest octane rating you can get ethanol-free, if that's available where you are), unless you have high-compression pistons or something like that.

PhilB

 

[DesmoDog]

I bought an M900 new in 1993, and ran it on 91 octane "to be safe". The first time we had the heads off, at 122K miles, there was a fair bit of carbon buildup from incomplete burning, due to running too high an octane rating. My mechanic scrubbed it all up, and told me to stop running premium -- fo to regular. So I did that, and it stayed cleaner inside for the next 140K.

So, just run regular 87 (or the lowest octane rating you can get ethanol-free, if that's available where you are), unless you have high-compression pistons or something like that.

Did your mechanic do anything to the engine other than clean it up? I ask because I've read comments like this before and they don't make sense.

Detonation is not due to the flame moving too fast, and higher octane gasoline does not control knock by burning slower. Detonation is caused by the mix autoigniting/exploding indpendent of any flame front. Dual plugs, MSD ignitions, swirl in the intake, all of that makes the mix burn faster. Why slow the gas down? Detonation is time related - burn the mix before it has a chance to explode (dual plugs, etc) or extend the time the mix can withstand high pressure/temp (raise the octane rating).

Anywhos, no flame (or pun) intended, but the theory that higher octane gas burns slower and has "incomplete combustion" goes against what is needed to prevent knock. And, numerous fuel companies have info stating high and low octane pump gas do not have significantly different flame front speeds.

All THAT said, I agree higher octane gas doesn't buy you anything if the engine doesn't knock without it.

 

[PhilBoncer]

Did your mechanic do anything to the engine other than clean it up? ...

Not to the top end. The main task was replacing the bearing in the alternator.

... or extend the time the mix can withstand high pressure/temp (raise the octane rating). ...

That's the key point -- doing that is what makes it burn less completely.

PhilB

 

[Charlie98]

Just for fun, I filled my 796 up with 107 octane racing fuel once... and it ran like crap. Granted, I wasn't taching it out every time I came off a stop, but it started hard and didn't run well. Back to normal with 91 octane.

Having said that... I have to buy non-ethanol fuel for my plastic tank Monster, unfortunately, I have to drive an hour to get it. I was somewhere they only had 87 octane non-eth... so I filled up on it... and within 5 miles my bike was knocking. Again... back to normal with 91 octane.

That's just my experience, YMMV. The rule of thumb has always been to run the lowest octane rating you can... without knocking. For my air-cooled 796... that's 91.

 

[MTScott2]

Brand name fuels from a brand name gas station.
Some gas stations may get cheap fuel from their supplier? Some stations may have contaminated underground storage tanks. A one time fill up should not be a deciding factor. Different areas have different fuels and seasonal additives... so many variables.

Up here many oil companies (Shell ESSO and Sunoco) use the same pipeline (hundreds of miles ) to transport their regular and hightest to the Fuel depot that MANY different tanker trucks use to supply many different brands.
They will ship cubic meters of hightest fuel from the refinery thru the pipelines to the depots huge cylindrical storage tanks (above ground) then switch to regular fuel without a barrier between the 2 grades, regular may have some hightest mixed into it , As long as it meets minimum specs, it is regular. Mid grade is a mixture of hightest and regular usually mixed at your gas station from the underground storage tanks. Hightest is hightest and sub spec hightest gets dumped into the regular above ground depot storage tanks.

Ethanol can be added at the fuel depots before or when the tanker trucks load.
I run tanks of regular every so often just because some say it is ok to use it and may have some benefits.

 

[haloguy628]

Brand name fuels from a brand name gas station.
Some gas stations may get cheap fuel from their supplier? Some stations may have contaminated underground storage tanks. A one time fill up should not be a deciding factor. Different areas have different fuels and seasonal additives... so many variables.

Up here many oil companies (Shell ESSO and Sunoco) use the same pipeline (hundreds of miles ) to transport their regular and hightest to the Fuel depot that MANY different tanker trucks use to supply many different brands.

Gasoline going out of a refinery sold to all companies is the same. The difference is additives. Those are mixed in the gas according to each company specs at the site in those above ground tanks you mention.

So no, the big brand gas is not the same. Independent non affiliated stations may have the same gas because they compete on price and therefore only add minimum amount of additives if any. It's always better to get branded gas because the additives it contains helps with preventing carbon buildup, has always at least the minimum octane rating and will not have contaminants, be it water or rust from storage tanks.

 

[Hillbilly Monster]

Did your mechanic do anything to the engine other than clean it up? I ask because I've read comments like this before and they don't make sense.

Detonation is not due to the flame moving too fast, and higher octane gasoline does not control knock by burning slower. Detonation is caused by the mix autoigniting/exploding indpendent of any flame front. Dual plugs, MSD ignitions, swirl in the intake, all of that makes the mix burn faster. Why slow the gas down? Detonation is time related - burn the mix before it has a chance to explode (dual plugs, etc) or extend the time the mix can withstand high pressure/temp (raise the octane rating).

Anywhos, no flame (or pun) intended, but the theory that higher octane gas burns slower and has "incomplete combustion" goes against what is needed to prevent knock. And, numerous fuel companies have info stating high and low octane pump gas do not have significantly different flame front speeds.

All THAT said, I agree higher octane gas doesn't buy you anything if the engine doesn't knock without it.

Yes,that's correct about detonation......The only non ethanol available is 90 octane so I'll just use that..Thanks

 

[DaveK]

Did your mechanic do anything to the engine other than clean it up? I ask because I've read comments like this before and they don't make sense.

Detonation is not due to the flame moving too fast, and higher octane gasoline does not control knock by burning slower. Detonation is caused by the mix autoigniting/exploding indpendent of any flame front. Dual plugs, MSD ignitions, swirl in the intake, all of that makes the mix burn faster. Why slow the gas down? Detonation is time related - burn the mix before it has a chance to explode (dual plugs, etc) or extend the time the mix can withstand high pressure/temp (raise the octane rating).

Anywhos, no flame (or pun) intended, but the theory that higher octane gas burns slower and has "incomplete combustion" goes against what is needed to prevent knock. And, numerous fuel companies have info stating high and low octane pump gas do not have significantly different flame front speeds.

All THAT said, I agree higher octane gas doesn't buy you anything if the engine doesn't knock without it.

Exactly, I think we've had this octane discussion before... easy way to think about it is "higher octane fuels have high resistance to pre-ignition and more uniform response under compression", and that lets manufacturers increase the compression to just below the point where the fuel will pre-ignite. If you have a lower octane fuel, that means some parts of it are more sensitive to compression than others... so manufacturers need to set the compression ratio of the motor to the LOWEST compression that the more variable fuel can tolerate, and that means less power. However... if the motor is designed for low octane then adding high octane does nothing because you're not compressing the air/fuel mixture beyond what the lower octane fuels can handle.

 

[ducvet]

The key here is what the motor wants.

All stock motors from the 90's were low enough to run 87 octane without a problem, if any need higher octane it would only be non-street legal bikes. Now carbon build up itself can cause detonation as it creates hot spots and yes added compression. Any aftermarket pistons are higher compression and will likely need higher octane but oem is not a problem if clean.

When my customers ask about this this is my method I recommend.

1. Run the tank down as low as you safely can and add 1 gallon of the next lower grade preferably from the same brand.

2. ride the bike somewhere you may be able to load the engine say climbing a hill in a taller gear.

3. listen carefully for detonation ( kind of like marbles in a tin can sound).
**** now some people cannot hear this for whatever reason if you are NOT sure have someone else do the test for you it is important to get this right ****

4. If there is none then run this gas for a bit and then repeat the test next time with another step down.

5. If there is detonation heard then go top the tank up with higher octane fuel.

6. since we know the bike SHOULD in most cases tolerate the lower octane we kneed to know why, start by running a diet of carbon cleaner through the system, Chevron techtron or OMC carbon guard work well.

7. after a few tanks of carbon cleaning , return to step 1 and repeat the test.

It was common to see bikes at the first service having intake valves that looked caked with carbon by 1000 miles, the pistons and combustion chamber were likely no different. Low rpms and high test fuels were usually the culprit as the new owner read the manual and as Phil mentioned the rating in the manual is NOT what is on our pumps in the usa so this was bad information. Usually once the customer was no longer babying the motor for break in and switched to lower octane fuel the valves cleaned up and life was good.

If you are buying a used bike you do need to be careful that it does not have oem pistons as there are plenty out there that we have modded and these bikes will need high test. If you are not sure or if you are buying high test for other reasons such a non-ethanol to protect no good,crappy useless plastic gas tanks then simply know you will likely be carboning up your motor and should make de-carboning a regular part of your maintenance. I would run a carbon cleaner through a few times a year at first and then if it is keeping clean you can reduce this to once or twice. Ever notice that when you buy "SUPER, PREMIUM" They include more cleaners , ever wonder why?

 

[DaveK]

Knock sensors are a wonderful thing... not sure why some bikes still don't have them (I think the Multi didn't get one until 2015). I also don't know why performance machines don't have user feedback when the ECU is retarding timing due to knock.

Back in the day I had a Turbo car that was the most efficient detector of stations that used cheap gas I've ever owned... it would kick timing back within 15 minutes of filling up at the wrong station. It taught me not to blindly believe that all 91 octane was created equal.

 

[Cowens726]

Ok so I've seen this discussion many times on many other forums but what I haven't seen is what consideration should be made if all you can get is ethanol laced fuel. Here in lovely "green" Oregon as a general rule you cannot get non-ethanol at the mainstream gas stations (there are limited hard to find stations that carry it but I was told by an attendant that they were not supposed to directly fill an on road vehicle, only gas cans and boats etc. it has to do with road emissions.) So I guess my question is would say 87 octane ethanol blend be the equivalent of 87 clear? I've only had my bike for a year and ran high test last riding season (mainly commuting and leisurely twisty trips) but I was planning on doing some testing and stepping down octane ratings this year. Since I have a steel tank should I worry about the ethanol other than during winter storage?

 

[duc96cr]

I have a friend who hauls gasoline to gas stations for a living. He explained to me that the normal procedure is to first put ethanol in the to 10% of the tank capacity, then find out how many gallons you are delivering and fill the tank with gasoline to that level.the result, of course, is that the least ethanol you will receive in your tank is 10%, but it could be much higher. This is done because ethanol is cheaper, but the excuse is that the ethanol must be mixed into the gasoline.
The ethanol free gasoline I have purchased in various States , according to the label on the pump, has been rated at a various octanes. I have no idea why. All of it has run fine in my S4RS, as does Premium ethanol diluted gasoline , which I’ve used out of necessity. Obviously I end up burning a mixture of ethanol and non ethanol fuel. Assuming 1 gallon left when the fuel light comes on, and I add $5 worth to get me home, I’m running about 5% ethanol or less. This has still resulted in the tank swelling if not burned off quickly.
My 900SS runs noticeably better at low rpm on non ethanol fuel. At higher rpm or throttle openings, I can’t tell a lot of difference.
My SuperGlide or Hayabusa do not care what I put in them, they run fine on any premium fuel.
My 77 Bonny is susceptible to carb problems on ethanol fuel, but runs fine on it.
I use SeaFoam additive in all my motorcycles, based on the recommendation of others.

 

[RockAZ]

Use as low an octane as you can without pinging.

 

[Charlie98]

I have a friend who hauls gasoline to gas stations for a living. He explained to me that the normal procedure is to first put ethanol in the to 10% of the tank capacity, then find out how many gallons you are delivering and fill the tank with gasoline to that level.the result, of course, is that the least ethanol you will receive in your tank is 10%, but it could be much higher. This is done because ethanol is cheaper, but the excuse is that the ethanol must be mixed into the gasoline.

I used to work not only as a gas delivery driver, but as a dispatcher for gas trucks... I am intimately familiar with ethanol-blended fuel... in some areas.

Most metro areas the loading racks are up to date... the ethanol is blended into the fuel as it's loaded, this is the only way they can certify the blend. All hell breaks loose if the rack shuts down and the blend is incorrect. Every state has their own requirements, and loading facilities in rural areas may not be up to modern standards.

Gas is not stored already blended with ethanol... it will separate in a fairly short time, that's why it has to be loaded as a blend and delivered promptly.

Gas is gas in most cases, it's the additive package that makes the difference.

 

[RockAZ]

Charlie98 has it nailed, here in the SW, you get these odd-job suppliers (especially out in the Reservations), that have scary mixes - If you have an old carb bike you have to be prepared to be thrown for a loop sometimes.

 

[duc96cr]

So why would it be bad to use fuel with a better additive package if I don’t mind paying for it ?

 

[Charlie98]

Charlie98 has it nailed, here in the SW, you get these odd-job suppliers (especially out in the Reservations), that have scary mixes - If you have an old carb bike you have to be prepared to be thrown for a loop sometimes.

That's also another issue... if you have to run ethanol-blend fuel, buy it from either a branded store, or a store with a lot of volume. Ethanol-blended fuel that just sets goes bad in 3-4 weeks... it's called phase separation and turns the fuel into junk.

So why would it be bad to use fuel with a better additive package if I don’t mind paying for it ?

It isn't. I think the OP's question was about octane. No-name stations rarely have additives, name brand stations usually (but not always) do, although sometimes the low-grade gas may not (Chevron does this.)