To fix of not to fix!

[Inyourdraft2000]

I was always taught that if it aint broke dont fix it. I have a 2000 400EX(stock) and It has never ran any gas other then 93 or 103 octane through it.
I read all the time in here where you guys are getting valve jobs done and differant things like that so I am curious do I wait till its broke or should I be taking this to an engine shop and have themm go through it.

Just curious because other then the stupid Carb dumping fuel out of the over flow tube it runs like a scalded dog.

[TRX450R_Racer]

If anything I would just check the valve clearance.

http://www.atvriders.com/articles/valveadjustment400ex.html

[qt314nfla]

IMO I wouldn't touch it till it breaks.  Two reasons no sence in messing w/ something that's already running fine.  The other reason is no sence in spending money on it till you need to.

[xr100racer]

adjusting the valves is easy. you should be able to hear ticking from the rocker box if you need to adjust them  if they have never been adjusted and its a 2000 model then you mine as well check them out. dont stress about it though if its running fine. you would be able to hear it if it got bad

and anything above 87 octane on a stock 400ex is a waste of money. it wont make it run better at all, higher octane is only required when you increase the compression to avoid detonation

[xr100racer]

and about fuel coming out of your overflow tubes - you could possibly check the float levels

[Inyourdraft2000]

Well I replaced the float and valve pin. If I wheelie or ride wild through the woods or jump it dumps fuel out pretty good.
As for the fuel being a waste I dont really run it for the performance as much as I do for cleanliness.
I have had the carb off several times and it looks brand new inside.
My dad has always ran 93 octane in his 95 f150 and he has obviously kept up on the oil but he has 340k miles on it. Lower octane fuel does not burn as efficient and will gum up inside your carb and even your Injectors.
Well reading the instructions on the adjustment looks pretty easy......

[KB]

On air cooled, 4 strokes you should only run 87 octane.
Actually a higher octane will run hotter.(not good)
On car's /truck's it's different 'cause there water cooled.