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Recently my bike cutout. I was riding along and then it just seemed to fizzle out the more I pulled the throttle back. After I got it started again it ticked over in idle but when I pulled the throttle it would gradually die on me. Eventually, it didn't start at all. I managed to get it to the garage via a carrier. The guy who fixed it said, as did two other mechanics, that it was probably clogged up from the use of supermarket fuel. He drained and flushed the carb, flushed the tank, and filled it with a higher octane fuel. It seems to run ok now (only had it back a day so far).

His parting advice was to use higher octane fuel to prevent this from happening. I don't get it. Help me understand. The idea that the bike doesn't like to run on standard fuel seems like a poor explanation. The bike was produced to run on 91 RON upward. I have always used 95 i.e. the standard fuel you get at petrol stations. The current bike is old (2003) but has had a service every year of its life and only has 6k on the clock. I have run it with standard fuel as did the first owner who never had the issue.
 

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For starters when your bike's manual was written, there was no such thing as ethanol added to regular gasoline.
Ethanol is to be avoided as much as possible. I don't know about the UK, but in my area, high octane fuel does not contain ethanol, and if you buy Top Tier certified fuel, you are getting a formula of additives that will clean your engine and keep it running better.

Was cheap fuel the sole cause of your problems? Maybe, and maybe not. But fuel is one thing I would not cheap out on. I pay the extra few cents and get ethanol-free, Top Tier fuel.
 

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For starters when your bike's manual was written, there was no such thing as ethanol added to regular gasoline.
Ethanol is to be avoided as much as possible. I don't know about the UK, but in my area, high octane fuel does not contain ethanol, and if you buy Top Tier certified fuel, you are getting a formula of additives that will clean your engine and keep it running better.

Was cheap fuel the sole cause of your problems? Maybe, and maybe not. But fuel is one thing I would not cheap out on. I pay the extra few cents and get ethanol-free, Top Tier fuel.
According to the esso website 5% is added to standard unleaded fuel for renewable energy efforts "The majority of unleaded 95 Octane petrol sold in the UK contains up to 5% ethanol as required under the Government's Renewable Transport Fuels Obligation (RTFO). There is currently no requirement for renewable fuel (such as ethanol) to be present in super unleaded (97 and 99 grade petrol)."

Fuel in UK is expensive (Gasoline prices around the world, 29-Mar-2021 | GlobalPetrolPrices.com) and high-grade fuel is well... more :) .... it's about managing money, and if it is not the reason for blockage then I don't want to spend it...

I doubt the reason given but it is undeniable that once it was cleaned out it worked - the reason itself is based on conjecture not solid evidence - I suppose I was hoping for a magical answer :p
 

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1st, octane rating is a measurement of how hard a fuel is to ignite, the higher the number, the harder it is to ignite. hi-compression engines need this (or a computer and knock sensor) to help prevent pre-ignition pinging/detonation. (where the fuel ignites too early from the hi compression itself or possibly hotspots in the combustion chamber.) The stock spark plugs in my 2004 Nomad were a range too hot, it pinged practically all the time on the high octane, simply dropping the plug heat range one step pretty much cured it. Probably should have gone 2 steps in hindsight and switched to the lower octane...

The old hot-rodder rule of thumb here with carbs was usually you need premium if your compression ratio was 10:1 or higher. And if it's not pinging, try dropping the octane level every tank or 2 until it does, then go back up one grade. As for the ethanol. avoid it if at all possible. if not, try to burn it as soon as possible and don't let it sit in the carbs. Maybe shut the petcock and drain the carbs if it's going to sit more than a week? I always opt for the ethanol free regardless of octane rating.
 

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You really can not make an octane determination on cr. I understand how that theory came about as the old flat head and overhead 2 valve engines needed high octane fuel. And yes cr was a contributing factor but the bigger cause was poor combustion chamber design and inaccurate fueling. Anyone who has ever removed a cylinder head from any of the millions of old v8 engines would remember how clearly visible the poor fuel distribution and flame propagation were. The generally accepted purpose of four valve heads is to increase flow but the bigger benefit is the swirl they create. Suzuki's first four valve heads were labeled TSCC, Twin swirl combustion chamber. Many of Mazda's na Skyactive engines run 12 and even 13 to one cr on 87 octane. If memory serves in the US 87 octane is specified for the EX500. The EX has a pretty good head design. Sometimes we have little choice on octane rating. Where I live the only non ethanol fuel is 91. I use Ethanol free in everything I own.
 

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ASTM standard D2700 specifies how octane numbers are determined. In short, they run the fuel through a test engine that has a variable compression ratio. Note also that ethanol will impact octane ratings.

Here are excerpts from the standard:

"This laboratory test method covers the quantitative determination of the knock rating of liquid spark-ignition engine fuel in terms of Motor octane number, including fuels that contain up to 25 % v/v of ethanol. "

"The sample fuel is tested in a standardized single cylinder, four-stroke cycle, variable compression ratio, carbureted, CFR engine run in accordance with a defined set of operating conditions. The octane number scale is defined by the volumetric composition of primary reference fuel blends. The sample fuel knock intensity is compared to that of one or more primary reference fuel blends. The octane number of the primary reference fuel blend that matches the knock intensity of the sample fuel establishes the Motor octane number."


I had the chance to witness an octane test in process at one of the largest refineries in Canada. It was fascinating.

The general consensus is that ethanol is bad for your engine. Most motorcycle manufacturers urge owners to use pure gasoline in their motorcycles. At least one motorcycle maker, Ducati, considers ethanol to be a gas additive and its use voids the cycle’s warranty.

I will only use ethanol-free Top Tier fuel in all my vehicles. Sadly the Top Tier system has not made its way to Europe yet.

Top Tier Gasoline
 

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You really can not make an octane determination on cr. I understand how that theory came about as the old flat head and overhead 2 valve engines needed high octane fuel. And yes cr was a contributing factor but the bigger cause was poor combustion chamber design and inaccurate fueling. Anyone who has ever removed a cylinder head from any of the millions of old v8 engines would remember how clearly visible the poor fuel distribution and flame propagation were. The generally accepted purpose of four valve heads is to increase flow but the bigger benefit is the swirl they create. Suzuki's first four valve heads were labeled TSCC, Twin swirl combustion chamber. Many of Mazda's na Skyactive engines run 12 and even 13 to one cr on 87 octane. If memory serves in the US 87 octane is specified for the EX500. The EX has a pretty good head design. Sometimes we have little choice on octane rating. Where I live the only non ethanol fuel is 91. I use Ethanol free in everything I own.
That's why it's the OLD rule of thumb,,, ;) The modern engine designs with the fancy combustion chambers and variable valve timing + the computer being able to move the timing around based on the knock sensor detecting the first signs of pre-ignition and oxygen sensors to correct the mixture pretty much threw out most of those old rules. The bike in question is a 2003 with carbs, While it probably has a better head design, don't think it has a computer...

I drive a 97 Celica GT 5 speed as my daily driver, DOHC 4-valve head with relatively high compression and fuel injection runs fine on 87, but better on 91. better yet on ethanol-free 91. The best mileage on it is with the ethanol-free 91, worst is 87 with ethanol. I still fail to understand how I'm helping the environment by burning inferior fuel. using 87 with ethanol, I lose 10% of my gas mileage. by adding 10% ethanol and burning 10% more fuel to go the same distance, what exactly did I do except make the corn-grower's lobby richer?
 

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And Nimai , our 87 is your 91 RON. They calculate our octane rating differently, its R+M/2 = research octane number (RON) plus mechanical (or motor) octane number (M) divided by 2
 

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You make excellent points 9094.

A friend of mine ran a test on a VW Golf that he used to commute to work every day. Same drive every single day. He normally ran regular with ethanol and he kept track of his gas mileage and he noted exactly what you found; You get more MPG with ethanol-free fuel. In fact, he calculated that with the extra MPG, it more than paid for the extra cost of the high octane, ethanol-free fuel. So in essence you end up with better fuel at the same price as what you pay for ethanol fuels.
 

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US spec EX500 has a cr of 10.8 to one and calls for 87 octane. Carbureted, not achieved by fuel injection or sensors. Liquid cooling and sound head design. Most aircraft engines have 6.5 to 8.0 cr but require 100LL fuel. My 77 302 Mustang two had I believe a cr of 8.5 to one and pinged on even high octane. Absolutely for test purposes if you take a dedicated test chamber and keep upping compression it will knock but that is a test chamber not being constantly redesigned to alter flow. Everyone has had to abandon the head design we used for decades. I agree ethanol is not engine friendly. Stores poorly and returns lower mileage. For any old Ducati or boat owners it also dissolves fiberglass.
 

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That is interesting about the Golf. I have always seen an improvement using non eth. but never enough to cover the additional cost. In my case paying extra even if the mileage was the same is worth it to not have that stuff in the tank. Modern cars run fine on the ethanol blend as they were designed for it but I admit to a strong bias against it both due to all the damage to small engines I have seen and the political boondoggle as energy in to energy out using corn is 1 to 1.
 

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I totally agree that modern engines with computers can adapt to run on almost anything, but performance and fuel economy will suffer. There was a very interesting petrol test done in England where they used a Golf and they bought various fuels from various suppliers to try to prove if HP was affected. If I recall correctly, the differential between best and worst power was more than 5 HP. The worst of course was ethanol blend regular and best IIRC was Shell V-Power.
 

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I went looking for the Golf HP test and found this instead. If you have a spare 6.5 minutes, it's a great vid. Apologies to Nimai for hijacking his thread.

 

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I totally agree with the lower gas mileage and performance when ethanol is used. My comment was poorly phrased. By run fine I meant no damage to gaskets, o rings, hoses and such which often happens with older engines. Also with the closed evap systems in modern cars moisture absorption does not seem to be a problem. In a system with direct venting such as most older motorcycles have with both the fuel tank and carb atmospheric vents open, absorption is much more likely.
 

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Apologies to Nimai for hijacking his thread.

No, this is great, I have learnt a lot by reading the conversation - it is very enlightening - I feel confident that spending the extra money on fuel will increase performance, save me money on future garage costs that may arise from this issue, extend mileage slightly (perhaps), and give me peace of mind. In addition, all the other interrelated topics...
 

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Interesting. From the article "...it takes 1.6 gallons of ethanol to do the same work as a gallon of gas".

Now we understand why fuel WITHOUT ethanol will contain more energy and yield higher horsepower and better fuel economy.

As far as I know, the format of ethanol subsidies may have changed but they still exist. One estimate was that it amounts to 6 Billion dollars per year for the USA.
 

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Recently my bike cutout. I was riding along and then it just seemed to fizzle out the more I pulled the throttle back. After I got it started again it ticked over in idle but when I pulled the throttle it would gradually die on me. Eventually, it didn't start at all. I managed to get it to the garage via a carrier. The guy who fixed it said, as did two other mechanics, that it was probably clogged up from the use of supermarket fuel. He drained and flushed the carb, flushed the tank, and filled it with a higher octane fuel. It seems to run ok now (only had it back a day so far).

His parting advice was to use higher octane fuel to prevent this from happening. I don't get it. Help me understand. The idea that the bike doesn't like to run on standard fuel seems like a poor explanation. The bike was produced to run on 91 RON upward. I have always used 95 i.e. the standard fuel you get at petrol stations. The current bike is old (2003) but has had a service every year of its life and only has 6k on the clock. I have run it with standard fuel as did the first owner who never had the issue.
Sounds to me like you had some water in the bottom of the float bowl. When this happens, the bike will idle fine, but when you transition to the main jet, the fuel is pulled from the bottom of the bowl. This causes the symptom you describe. Ethanol in fuel will cause water to form more readily than non-ethanol fuels.
 
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