what octane should i run? ive been running 87 because of the HIGH prices but i want to run what i should be. would higher like 93 give me anything noticeable?

 

Not unless you raise the compression.

 

I don't know about your owners manual, but on page 84 of mine, it specs 92 OCTANE OR HIGHER! Around here, 91 pump gas is all that is available, so I add enough Klotz Octane Booster to get it to 93, for a little extra margin.

Your EX is air cooled (maybe sometimes paryer cooled), and air cooled engines run hotter than water cooled. Therefore, you are more prone to detonation, hence you need a higher octane, even though your compression isn't at all outrageous.

 

Thats funny, I've never seen any production ATV from the big 4 require anything more than 91 octane and thats only on some two stroke and high perfromance 4 strokes. I understand the concerns about air cooling, but I wouldn't think it would require race gas on a stock bike just because its a hot day. If you're running that hot all of the time there's mostl likely a problem.

 

Considering it is only a three gallon tank I would run the minimum 91 octane. Even if the prices are high it would only be $0.60 difference per full tank!

 

But even 91 isn't enough, especially in hot Nevada summers. You are also going to need a little bit octane booser.

 

ok i am not honda man buti know for a fact any fourwheeler will run fine on medium grade. Yes it is better with 91 but medium is fine and oh yea p.s. YAMAHA ROCKS

 

well... my tank was about 1/4 full with regular but i put the rest premimum. When i fill it up fully with premimum.. i will see how it runs.

 

guy i no runs 87 in his 400ex with pipe no problem runs just as good as one with 91 octane....87 actually prob more power

 

Play it safe and run 92, no matter what anybody says. Detonation is BAD for your engine!