Why does my 400ex feel weaker?
 

Today I noticed that my quad feels much weaker than before. By weak, I mean it's torque is really low. I haven't done much to the quad except fill the tank with Premium gas today and clean the air filter. Any clue what it is? This is my first time running on Premium gas so I don't know if the gas affects it.

P.S. I also noticed today that my clutch is fairly hard to pull in.

I don't think running premium gas is causing your problem. I believe the stock 400ex compression is 9.1:1 or something like that so it should run fine on premium. You may not need it, but it won't hurt.

You say the clutch feels slightly off suddenly? If the clutch is slipping that will greatly impact your torque getting to the rear wheels. I would try adjusting the clutch to see if anything changes.

Read your owner's manual! Mine says it REQUIRES 92 octane or greater!!!

Folks who base octane on compression alone are simpletons. There is way more involved in what octane you need, besides just compression. Things like is it air cooled so it runs hot, valve overlap, etc., etc.

That said, you could have gotten bad gas. Your air filter could be leaking or not installed properly, which make you run lean. Other subtle changes can make a difference as well, like air temperature, humdity, etc.

Your just used to your ATV,time for a 450R. When you get used to the 450 then get a 525 KTM powered ATV. Its the never ending story of motor sports.

Since you mentioned the clutch feeling different, there is a possiblity of some damage in the basket,or springs in the clutchpack, a bad drag in the drivetrain would defineately cause some power loss,that may need some more looking into.
I won't even comment on the gas octane, certain members on the forum are sooooo touchy about that.

What is odd is that I've seen a lot of people run regular in their 400ex....... Yes there is more to octane then compression, but that is the main driving factor as you well know. If your "simpleton" shot was at me it was misguided. I was speaking in context, based on the fact that I've run into many riders of 400ex machines who run regular, I'm not saying its right, but they will obviously run on it. I was just pointing out that suddenly running premium would not hurt.

Don't worry, ss97, ol' Recon has this thing for Honda oil and premium gas being the cure all for all the world's ills, if you don't agree with him, you are a simple minded moron for not bowing down and praising his words. I have a 440 ex with 11:1 piston, since Reconranger says the stock 9:1 NEEDS premium, my built motor must need something in the neighborhood of nitromethane or rocket fuel,yet it runs very well on 92 octane premium,and has done so for several years. But that is using compression to dictate octane requirements, oh,God, what have I done ??? now the wrath of the mighty "R" will be upon me !!!!!! (yes, I'm laying it on a bit thick, but I've just about had it with his rants and insults to anyone who won't agree with him) Oh, and by the way, if you ride a ute, you are a hillbilly in his book as well, just don't run 87 octane in your ute, or the very fabric of the universe could well unravel !!

Honda oil???? Give me a break! I have not run Honda oil for a decade since it went API SJ (vs SG) and got downgraded levels of ZDDP so it could be run in street bikes with catalytic converters.

Nothing but ester synthetic Redline or maybe Maxima Extra/Ultra/530MX for me!!!!

As far as octane goes, run what your owner's manual specs not what some hillbillies suggest!!!

idk just read their opionions and you have to suggest what to do from there, both seem to have points