i have a yfz450 with an esr airbox eliminator stock exhaust and a 160 jet.
It bogs whe the choke is fully out and fully in but runs like a champ at 1/2 choke.

whats the cause of this??? and no air leaks as far as i coule tell

 

a 160 jet sounds a little small to me. You might be running a little lean. Not sure where your at (altitude) but if you have more air than stock you need to rejet your carb.

 

i live in oklahoma.. but rejetting willnt be a problem how big should i go??

 

I run a after market exhaust, pro-flo kit with lid off. Have a dyno-jet 165 in mine. dyno jet recommends a 160. Not sure the equivalent in Keihien but would'nt think you were far off. Explain this bogging. Does it just cut out or is it a lack of power? I'm guessing it does the same thing with the choke in?

 

I am running a similar setup to yours, with a 170 main and 45 pilot at sea level.

 

it acts like its going to die then i let off the throttle a bit and then it goes it does it choke all the way out and all the way in but at half choke it doesnt do it

 

When one runs rich it usually don't cut out like that. It will seem sluggish and not have power but will run ok. If its trying to die its a diff issue.

Mine had an issue where it would cut out when I was at high rpm's. My plug was failing. Put in a new plug and fixed the issue. I know that would'nt explain your 1/2 throttle thing but, plugs are cheap and easy to install.

Early yfz's had stator issue's not supplying power I've heard. Hope thats not the issue. I'd start with a plug change.

 

i went down to brians atv here in oklahoma and talked to them about it and they said i need to hollow out the stock muffler with a 1 3/4 hole saw and we put a 178 main jet in it and the 3 passes down the street seemed like that did the trick so far but the road is wet so it gotta lot of tire spin..

 

with a 160main you would be a little rich, your choke leans it out, which is why at 1/2 choke that would correct your richness a little bit, i would think that around a 170-175 and you should be good.

 

<div class="FTQUOTE"><begin quote>Originally posted by: DesertYFZ450

with a 160main you would be a little rich, your choke leans it out, which is why at 1/2 choke that would correct your richness a little bit, i would think that around a 170-175 and you should be good.</end quote></div>

The choke adds gas, there guy.