after riding for a few hours the other day i went to take off and i gave it 1/2 throttle and it started bogging down from 1/2 to full throttle. i was wondering if it is possible for it to get to hot and not run right? i thought maybe i had some dirt in my needle valve, but when i got home it started right up and ran fine so im out of ideas.

 

The first thing you have to eliminate is how clean the fuel system is. You should take off the carb, disassemble it down as much as possible, then use compressed air to blow out all the holes in the carb. If it was sitting for a few months like for example after winter riding you should dunk it in carb cleaner solution to remove any gummed up deposits.
The other things people tend to leave out is the fuel source(tank). You need to have this clean, because as soon as you clean the carb and put everything back together, your still feeding it with dirty fuel. So I would remove the fuel tank and clean it out really good, even remove the fuel petcock and clean the screens if you can on that model. After doing so you will now know you have fresh fuel and a clean carb. If it still doesn't run right then you start messing with needle settings, main jets, mixture screws & float level.

 

what about the possibility of it getting to hot or is that out of the question.

 

If you think your running hotter than normal you might have issues like... running too lean, oil cooler and or cooler lines plugged, low on oil, oil filter or an oil passage clogged. Do you change the oil on a regular basis?

 

Does your fan ever kick on? If not, look to see if it has come loose from riding. Just follow the line down, from the fan, to connect it.

 

the 400's don't have a fan, but i have thought od tryin to put one on it

 

An engine requires 3 things - fuel, spark, and air. I always start with the most obvious or cheapest first. Change the spark plug. If that's not the problem then you may have a fuel related problem. The first time I had a plug problem the same thing happened to me. It would start fine then once I gave it a rev it died. I changed the plug and it was fine after that. Hopefully thats all it is.

 

My Rancher AT 400 has a fan. Maybe you have a EX.

 

Yea, clean ur carbs first. Put some fresh gas and a new plug in. More than likely that will fix ur prob. Prolly wouldnt hurt to change ur oil if you havnt done that in awhile.

 

well, come to find out that my 400EX is bored 20 over. well buying it used i didn't have any idea what was done to it. so i called the shop where i had some work done to it because it was smoking really bad and they told me that when they tore the top end apart it was already bored 20 over and i didn't know it. so that helps alot. also the guy i bought it off of said it hadn't been ridden in awhile it was his son-in-law's quad. so that answers a few questions, so i'm thinking it has sat to long and either got some dirt in the carb, or possibly a trace of water, so im off to buy some dry gas to get rid of the water and some carb cleaner. the plug was just changed about 3 weeks ago but i may check that again. does anyone kow if you have to take the tank off to do that? from what i was seeing you do but i don't know for sure. also, i have been running 87 because i didn't know about it being bored out so i'm gonna start running 93 octane that should help a lil to.