What Octane does your bike need?

[Bonz]

Bonz,
C14's have a factory warning sticker on their gas tanks that advise using a minimum of 90 octane.

I have, at times, ran 87 ethanol. If the temps are cool, I haven't noticed any pinging. But, temps ranging from the 90's or higher will cause it to ping under heavy acceleration. Doesn't do it using 91-92 octane.

I've also ran the 85 octane in Colorado with no ill effects. But, higher altitudes there, too.

Lots of variables can affect the result. Compression ratio, temp, altitude...
.... heavy right hand... Lol!

I'd think you need higher octane for that ZRX now...even at higher altitudes?
Bob

In talking with guys that have more experience than me (specifically a fellow who makes and sells the +2 and +4 advancers for the ZRX and has done lots of experimenting) 11.0:1 is the highest CR based on the ZZR piston and combustion chamber design to use regular gas. And that is only if it doesn't knock/ping. I cleaned the combustion chamber when the head was off and the pistons were shiny like new, so initially it has the best chance to do fine with lower octane gas. In reality, it is on the edge and as I haven't had temps over the low 70's yet out here since the CR increase, I am sure warmer temps will dictate moving up to the next level.

However, given the approx 25% thinner air at 7000', that is a lot less O2 to worry about in leading to pre-ignition. Which gives more margin for increasing CR from 10.0-1 to 11.0-1 and not having issues that you flat landers would.

And man, does the bike ever like the increased compression with the ZZR cams I had already put in there!

[XJkid]

Carbon buildup?

I read in a thread on here that using premium would buildup excess carbon. I had been running premium in mine, so I checked. Sure enough, I had buildup that I could scrape off with a screwdriver through the spark plug hole. I put regular in it and rode it hard, carbon gone!

[Bonz]

Thanks Xjkid. That is real proof as to what I have heard and been talking about as well with regard to running higher octane than what the engine tells the rider it needs.

I would venture to guess bikes that have been running High Octane and pinging when a rider puts in lower octane, could have carbon buildup in the combustion chamber for some of the same reason as build up on the exhaust valves therefore leading the owner to believe it won't run properly on lower octane.

Carbon, no matter the cause of it, takes up space in the combustion chamber raising compression ratio and promoting hotspots that lead to pre ignition. By eliminating the carbon you have shown the bike can run properly on regular octane.

[MPittma100]

Carbon?

I read in a thread on here that using premium would buildup excess carbon. I had been running premium in mine, so I checked. Sure enough, I had buildup that I could scrape off with a screwdriver through the spark plug hole. I put regular in it and rode it hard, carbon gone!

Is it possible that if you "rode it hard" with the higher octane that the carbon might also be gone?

[willem.deboer]

I'm with you Mike...corn should be on my plate or in my moonshine ...not in my gas tank...I avoid using ethanol gas as much as is possible...Theres a non ethanol station 4 miles from me...

There's a lot of discussion on this subject. But my 2004 Mitsubishi Spacestar started producing errors in its engine's computer when using E15. Lambda Sonde producing values outside factory tolerances. No warning lights, but still. I love my OBD2 dongle :-)

[XJkid]

Is it possible that if you "rode it hard" with the higher octane that the carbon might also be gone?

Possible, but the fact that the carbon was there to begin with makes me suspect premium fuel.Time will tell for sure.

[SS Clift]

Ethanol can be a real "pain in the ass" since it eats carb diaphram rubber on older bikes and some fuel tank sealers (ie Kreme ) . It absorbes moisture ( water vapour ) which can rot out fuel tanks, if stored for long periods , make gas " skunky" and plug up those tiny jets in your carbs. My recommendation is to buy the lowest octane fuel ( octane is a "knock" inhibitor....not a power booster ) that contains NO ethanol .
Check out www.pure_gas .org for listings of gas stations in Canada & USA that sell ethanol free gas.

[Bonz]

Possible, but the fact that the carbon was there to begin with makes me suspect premium fuel.Time will tell for sure.

I think what you are saying is the carbon was there, in what you think to be an excessive amount, and was a result of burning premium fuel. For the same reasons exhaust valves can carbon up with premium fuel in a lower compression motor like the XS.

It is very possible running it hard regardless of the octane might have or would have done the same thing. However again, this shows burning premium fuel were not specified or needed could have contributed to or been responsible for the carbon buildup that was there. The fact that it is gone now is a good thing, however the root reason it was there in the first place potentially leads back to the octane component.

Found a good explanation here:

"Fuel octane and the quality or type of fuel used in an engine can also be an area of concern. Driveability Index (DI) is a measure of gasoline’s total volatility, or tendency to vaporize completely. A high DI number is less volatile than a low number. Premium grade gasoline is rated at a higher DI (less volatile) than regular or midgrade gasoline. Since fuels with a higher DI number or octane burn more slowly, higher compression ratio engines typically use higher octane fuels to avoid heat-induced preignition. Conversely, when using a high-octane (less volatile) fuel than an engine was designed for, fuel will burn too slowly, resulting in incomplete combustion, increased carbon deposits and driveability concerns such as increased cold start, warm-up sags, hesitations and stalling at moderate ambient temperatures"

[MPittma100]

Not One

Not sure what all this concern about carbon has to do with anything. Every engine's combustion chambers/piston domes always have carbon on them.

[Bonz]

I agree with you 100%. It's when excess carbon begins to accumulate the issue rears its head. To my thinking, if the carbon was there and then run hard to clear it, excess carbon had accumulated.

[willem.deboer]

Ethanol can be a real "pain in the ass" since it eats carb diaphram rubber on older bikes and some fuel tank sealers (ie Kreme ) . It absorbes moisture ( water vapour ) which can rot out fuel tanks, if stored for long periods , make gas " skunky" and plug up those tiny jets in your carbs. My recommendation is to buy the lowest octane fuel ( octane is a "knock" inhibitor....not a power booster ) that contains NO ethanol .
Check out www.pure_gas .org for listings of gas stations in Canada & USA that sell ethanol free gas.

Soon, in Holland we won't be able to buy fuel without ethanol. In Belgium they have already taken this step. Only 95 (RON) unleaded available there is E10. Would I then have to start filling up with 98 (RON)?

[Bonz]

The octane will be the same, it's just the ethanol potentially can cause issues that has been brought up already.

My feeling is ethanol is more of a problem in hot and humid climates versus cooler climates. I live in Colorado, E10 is pretty much all we get in every grade. While it gets really hot, the humidity is low. I simply keep fresh fuel in the tank by riding the bike and add Stabil stabilizer over the winter months when the bike is ridden once a month or so. Zero issues on any bike, carburetor or fuel injection, in Colorado for the past 12 years.

[TopCatGr58]

Hey Bonz,

This carboning up problem, and the discussion about running it "HARD" to burn/blow it out made me think a bit. Many times I have encountered XS11 owners and riders at the rallies, and they want to ride their bikes like they are H-D's and are AFRAID to run the rpms much over 5K, and they want to LUG the engines at 2K rpms. I know the engines have power and torque and can run at that speed, but it's detrimental to the bike both with regards to the tendency for carbon buildup as well as draining the charging system since doesn't reach it's full voltage/amp capacity until at least 2500 rpm or more.

After my big bore rebuild in 2000 I ran 93 Premium in it exclusively for some 15 years but never had carboned up or fouled spark plugs. I do run a HI POWER/OUTPUT set of coils that help to provide a strong spark. I also habitually run mine at 3500 rpm or more and have no problems running it at 5K+ on the highway for hours.

SO...I postulate that part of folks excessive carbon buildup comes from running their engines at too low of rpms when putting around town and such. JAT!

T.C.

[MPittma100]

Carbon

"SO...I postulate that part of folks excessive carbon buildup comes from running their engines at too low of rpms when putting around town and such. JAT!"

You are 100% correct T.C. And that goes for cars and trucks as well. Any engine, any fuel will yield carbon from combustion. The amount in an engine is determined by how it is driven. Ever hear the term "I need to blow out the carbon"?

T.C.[/QUOTE]

[Bonz]

I agree wholeheartedly that running a lower RPM in higher gears can introduce carburetion and ignition dynamics that are not optimal for a clean burn. A lifetime of that oils sure build up deposits over the long haul. Running the proper grade fuel will keep that at bay as much as possible. I would guess running too high of an octane and babying the bike would exacerbate what we have been talking about.

I talk a lot about the work I have done on my ZRX 1200. When I pulled the head to do higher compression pistons this winter, The combustion chamber had normal carbon, the exhaust valves had no carbon however the intake valves were thick as thieves with carbon on the back of the valves and stems. For the past 4 or 5 years, I have been running a bit of TCW3 two-stroke oil in most every tank as I read much about how it helps with minimizing effects of ethanol on a fuel system. I was guilty of "if a little is good, a bit more won't hurt" and attribute the carbon buildup to overuse.

With your big bore TC, can you recall the advertised compression ratio that came with the pistons?