92 unleaded really?

[Jakeyracer]

I went out riding a long while back w a friend who had a yfz. she noticed that my ex has almost like a small gear whine sound at idle and I noticed it long ago when I had first rode it but figured it must be normal because it ran fine and still does, but she claimed if I ran the highest pump octane insted of basic unleaded that the noise would go away

now she's not ordinary... she's a licsensed mechanic but well let's put it this way if she would stick to "if it ain't broke, don't fix it" she would still have a toyota pick-up and that yfz so this gives me reason to question her theorys

so is this true highest octane will rid me of the noise or is my ex gonna wind up like her yfz if I listen to her

[slightlybent47]

Well thats easy. buy a gallon of 93 and try it out.

[CarGuy7a]

IMO the book recomends 92 or higher for a reason. My buddy ran regular 87 in his and it ran like crap.

As for the whinning sound. Mine does the same thing. I believe it's the sound from the oil pump. Mine's done it since brand new so I'm not worried about it.

[TRXRacer1]

Originally posted by slightlybent47
Well thats easy. buy a gallon of 93 and try it out. Agreed, it's not going to hurt anything to try.

[CJM]

I usually run 89 or better.

87 Octane has to much ethanol in it apparently and can cause issues.

[Ryan'07400ex]

I went to harlan and had 93 octane in it the first day ran good didn't hear much ticking... then the next day filled it with 87, I felt like it was ticking much more and much louder. Im guessing thats what it was from or it could be it was just the second day of being rode hard idk.

[katch26]

Originally posted by Ryan'07400ex
I went to harlan and had 93 octane in it the first day ran good didn't hear much ticking... then the next day filled it with 87, I felt like it was ticking much more and much louder. Im guessing thats what it was from or it could be it was just the second day of being rode hard idk.

well that answers my question

[Jakeyracer]

Originally posted by CarGuy7a
IMO the book recomends 92 or higher for a reason. My buddy ran regular 87 in his and it ran like crap.

As for the whinning sound. Mine does the same thing. I believe it's the sound from the oil pump. Mine's done it since brand new so I'm not worried about it.

well i dont have the manual so i wouldnt know but the oil pump sounds like a good explanation... and my all the quads and trikes weve had run just perfect on 87 oct and were talking over a span of 13 years so i dont think its to harmful considering weve never rebuilt any of our quads and never had jetting issues. but if i ran 93 would i have to monkey around w jetting at all?

and also these dial a jet kits... how easy are these to install and would it be a good idea on a stock ex?

[CarGuy7a]

Na you shouldn't have to mess with the Jetting. Really the only time you need to mess with jetting is either extreme altitude changes or when you start adding exhaust systems, higher flow air filters, cams, and stuff like that.

Really what determines what octane you should run is the compression. Lower compression you run lower octane and vise versa with higher.

I think the 400EX has like 9.5:1 compression (someone correct me if I'm wrong it's been a while since I've looked it up) and I remember reading in the book it said to run 92 or higher.

The reason is if you run too low an octane your engine can actually have pre det or pinging and possibly ticking sound (not to be confused with the normal 400EX valve tick). It's when the low octane fuel ignites under compression and before it's supposed to be ignited by the spark plug.

[Jakeyracer]

so quite possibly i could be burning up my piston... maybe i should check it out just to be sure... :ermm: but theres no ticking just a whining noise at idle its really slight and consistent

[miles Machine]

that slight whining noise is common in the ex's if its the same noise that your describing mine did it and alot of them ive herd do it...its kind of a cam chain whine

[grovesbm]

use 93 like they say in them books where all the real important stuff is

[grovesbm]

burns cleaner unless u leave them books in the jug after honing/boring

[riotact]

Originally posted by grovesbm
burns cleaner unless u leave them books in the jug after honing/boring :huh

Your piston is fine.Just run some 92 in her and see if it changes anything.There's no point in rebuilding it if it still has power and doesnt smoke.

[TRXRacer1]

Originally posted by Jakeyracer
so quite possibly i could be burning up my piston... maybe i should check it out just to be sure... :ermm: but theres no ticking just a whining noise at idle its really slight and consistent What's so difficult about selecting a different octane when your already at the pump? Just do it.