Best octane to use in xs400

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firemanbob

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Hey folks! I have an 82 xs400 Special, with nothing aftermarket on it. I've tried my google-fu and haven't found a concise answer. Would you all recomend regular unleaded or high octane? Also does ethanol affect performance in any way? Thanks in advance!
 
Regular unleaded should be fine unless you have seriously retarded the timing or you are running higher than stock compression.

Ethanol is more of a problem with rubber and plastic parts and dislodging sludge than performance, but a bike running E-10 will want a richer fuel/air mixture. As always, I suggest an external fuel filter, but since ethanol can dislodge varnish and sludge, it's even more important.
 
Last edited:
The bike calls for 91+ octane. I use 93 with yamaha fuel med for the ethanol and every once in a while some lucas fuel conditioner. 15yrs and no issues:)
 

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There are many gas stations now selling ethanol free 91 octane. if you find one nearby, uses it.
If not run the highest octane you can find. At least 91.
This can help prevent engine knock. And at sustained higher speeds can help prevent holed pistons.
Leo
 
HoughMade said:
Regular unleaded should be fine unless you have seriously retarded the timing or you are running higher than stock compression.

Ethanol is more of a problem with rubber and plastic parts and dislodging sludge than performance, but a bike running E-10 will want a richer fuel/air mixture. As always, I suggest an external fuel filter, but since ethanol can dislodge varnish and sludge, it's even more important.
Click to expand...

I agree, nothing special about these little motors. I run 87 that has a 10% blend during the riding season since I'm filling it up every week, however, over the winter I will put E-free in to help avoid any storage problems.
 
oddly enough the lowest octane you can buy here is 95. So I just go for that :laugh:

guess at 1.82 euro/liter you do pay for the higher octane as well :yikes:
(that's 9.52 $/gallon US or 2.78 canadian dollars/liter)
 
find a gas station that sales non-ethonal fuel. we have a few in my area you may also. its about the same price. as for ethonal it provides less power/performance.
 
IDK where you guys are finding gas stations here in the states that don't sell 10-!%% eteohanol blend,there sure isn't any around here in Michigan that I know of.:shrug:
 
everything for the most part in the states has up to 10% ethonal blend. ask the gas station about the ethonal blend content. unless michigan is different, probably not.
 
I'm pretty sure Marathon is E Free. I had a friend that had a high compression engine Acura and he always had to fill up at Marathon because of it. I have also never seen a Sticker at their tanks saying they have 10% Ethanol either.
 
they are probably not E-free. most large companies are not E-free. they are more into profit than they are the performance of your engine.
 
After googling it, it seems that you would be right although Marathon does market both. Also, the web site in the previous post, many of the E-free stations are Marathons so it is more likely that your local Marathon station would be E-free compared to other gas stations but you would still have to check.
 
willem said:
oddly enough the lowest octane you can buy here is 95. So I just go for that :laugh:

guess at 1.82 euro/liter you do pay for the higher octane as well :yikes:
(that's 9.52 $/gallon US or 2.78 canadian dollars/liter)
Click to expand...

Octane is measured differently in Europe than in North America. Your "95" is about 90 or 91 here. There's no direct equivalency chart, but that's about what it works out to.

In Europe, the "Research Octane Number" (RON) is used and displayed on pumps. It is determined in a lab with a test engine that has variable compression.

A second method is the "Motor Octane Number" (MON). It too uses a test engine, but the testing conditions are different to try to measure knock resistance under load more accurately. There is no direct formula to convert between RON and MON, but MON is usually 8 to 10 points lower than RON.

In North America, the number displayed on gas pumps is and average between RON and MON: RON+MON/2. This means that a gasoline with an RON in Europe of 95 may have an MON of 85. 95+85/2= 90 which is what will be displayed on pumps in the U.S.

So, overall, Europe isn't really getting "the good stuff"....their governments are just making their people pay for it as if it was.
 
willem said:
oddly enough the lowest octane you can buy here is 95 ...
Click to expand...
Europe supposedly uses the "RON" rating scale.
North America uses an averaged rating called "AKI" which is supposed to be a better measure of how the fuel performs when the engine is under load. So naturally, numeric values don't match.
 

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