I have a 07 yfz 450.  I am having a few problems out of it and its getting aggravatin.  First off my fan is wired to run anytime the quad is running. Well I just bought a new battery and it is already run down. The thign is so hard to start. I have a curtis sparks exhuast and the guy said he jetted it and everything.  I have no clue as to why it is so hard to start though cause it has a brand new battery and i just put a new spark plug in it.  The other day I had to hold my hand over the exhaust hole on the muffler to get the quad to start.  not sure why that did it but it did.  I let it warm up for awhile and took it for a ride i putted around the yard for a few minutes then took it down the road and it ran fine.  Well on the back I took it up to 4th gear and when i started letting out it started back firiing.  I kept it rev. up and then just as soon as i didn't it quit on me and wouldn't start back up.  I tried so much to start it it ran the battery down and I had to jump start it with cables and it ran fine.  I road it around the yard and brought it back in and it wouldn't start again.  If anyone has suggestions on what might be wrong and what I could do my ears are open.    

what did you do to wire the fan to run at all times and why? My yfz is jetted and piped and mine doesn't get so hot that I need the fan the whole time. My fan actually kicked on for the first time last weekend when I was riding at the coast. I ask because I think that the wireing is just sucking up all of the juices in that battery along with starting it so much. This is just my thoughts from reading your info. Sorry if this doesn't help.  

not for sure why it is wired up like that the guy that i bought it off of did it.  I have no clue as to how to wire it back the way it is suppose to be.  I would have just put a colder plug in myself but oh well.  Has yours ever had problems starting at all or the battery running down at all?  

No I haven't. Not yet at least.