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Fuel octane rating for Husky TX300


Toby_
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G’day everyone...

I was chatting with a mechanic today and we got talking about fuel and octane ratings. To my surprise, he said that for my bike (2017 Husky TX300) - it would  run better with 91 octane fuel, compared with 98 octane  

His reasoning was that 2 strokes are generally low compression ratio, so having higher octane is not needed because pre-ignition isn’t a factor, and in his experience 91 octane fuel will make most 2 strokes run better and that it’s all marketing hype that 98 octane fuels are cleaner and better quality compared with 91.

So I wanted to see what other members thought about this?  I’d like to get restponses from members who have personally tested different fuels on recent model 2 strokes - preferably husky’s or ktm’s.

Also note- I always use BP fuel  

Thanks very much, Toby

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Toby I ran my 2008 wr250 husky on 91 from new right up till I had the squish done which changed the compression.

The bike then ran better on 95. It would run on 98. But it didnt make any noticable difference so in my mind wasnt necssary.

This bike did over 14000 hard ks using lower octane fuels.

 

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Hey Toby, go 95 as it is a slightly more controlled burn/flame front and seems best for 2 strokes from my experience. Not sure if I am imagining it but Shell fuels seem to perform poorly for some reason so I dont use there fuel in any of my bikes. 

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Thanks for the replies guys. I will try 95 and see if there’s any noticeable difference. 


95 gives you a bit of protection from a bad batch of lower then advertised octane fuel and will run better then 98 on a stock 300.
Also switching to 91 to stop plugs fouling is a bandaid for an another problem. Plugs foul from a number of things like riding to slow,incorrect oil type or ratio for terrain or riders pace,float height to high,sticking or leaking float assembly but mostly from poor jetting.
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95 gives you a bit of protection from a bad batch of lower then advertised octane fuel and will run better then 98 on a stock 300.
Also switching to 91 to stop plugs fouling is a bandaid for an another problem. Plugs foul from a number of things like riding to slow,incorrect oil type or ratio for terrain or riders pace,float height to high,sticking or leaking float assembly but mostly from poor jetting.


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Yeh I agree Cluffie about the carby issues. I’ve had it into 2 shops trying to tune it correctly cause I’m no good at it. Second shop eventually improved it and put me onto a different plug but still a lot of spooge. The octane change came later and has also helped. Now only replacing plug every third or fourth ride instead of three every ride.

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Yeh I agree Cluffie about the carby issues. I’ve had it into 2 shops trying to tune it correctly cause I’m no good at it. Second shop eventually improved it and put me onto a different plug but still a lot of spooge. The octane change came later and has also helped. Now only replacing plug every third or fourth ride instead of three every ride.

 

Most bike shops are hopeless at jetting and have no idea. You need the expertise of a good engine tuner that has experience with the said bike you have and the carby it runs.

3 plugs a ride would be a nightmare. I'd be pissed fouling any. Those small ktm's are problematic though,i see it all the time at our local track and i'm regulary helping the kids trying to start them and pushing their bikes off the track once they stop. Stators are another nightmare,keep one in the toolbox.

Once the kids are on a 65 or 85 there's a sigh of relief from the parents,lol.

 

 

 

 

 

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8 hours ago, MrNoodle said:

I have always run 98, so 95 is the go for my 250 exc then? Running motorex at 50:1

if running the stock head 95 (91 is a bit hit and miss) .

sx or high comp head run 98

for sand/desert trips run 98 for extra detonation protection, richen the jetting on needle and main jet and up the oil ratio to 40 to 1 for 250/300. (this is important and could save your motor)

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Nah, not yet. I’m not sure if I need to? The bike has plenty of power. I’ve actually started riding it with map switch on the number   2 setting (Less aggressive) – seems to hook up a bit better in loose stuff. Might be placebo though?  So by doing the head, it might have more power, but will actually get it to the ground? 

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4 hours ago, cluffie said:

if running the stock head 95 (91 is a bit hit and miss) .

sx or high comp head run 98

for sand/desert trips run 98 for extra detonation protection, richen the jetting on needle and main jet and up the oil ratio to 40 to 1 for 250/300. (this is important and could save your motor)

I'm happy to run 98 as that is what goes in everything, the cost isn't a factor when it comes to dirtbikes. I just want whats best for the bike going forward

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28 minutes ago, MrNoodle said:

I'm happy to run 98 as that is what goes in everything, the cost isn't a factor when it comes to dirtbikes. I just want whats best for the bike going forward

Yeah, but if 95 makes your engine run better for what ever reason, then surely you would run 95 instead of 98?  From what 1 or 2 people have mentioned here, 95 might be the better choice for certain two strokes 

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my 2c

Its important to note that the return wave from the expansion chamber will affect the pressure level inside a cylinder, so while compression ratio's are lower on a 2t, its operation will result in more mix being ignited in a smaller area, just like higher compression. 

So it stands to reason that in some circumstances, the configuration of porting, ignition timing, rate of burn and temperature can all make noticeable differences in performance depending on the burn rate of fuel, or changes in temp (thus the speed of the expansion chamber return wave) caused by it.

I'm not an expert in fuel blends though, someone else will have to chime in as to which blends burn at what rate, and which additives cause this if at all.  It may be something is added to the higher octane fuels that affect something in this department, if not, the change in octane is just causing placebo benefits unless it addresses knocking. 

All of the above may be negated if you don't adjust your A/F screw each ride, I'm pretty sure that would make a bigger difference to performance.

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