Ok thans for all the help. I started with the easy stuff first. I mover the needle down a notch and a/f screw in a half turn and it got worse. I moved the needle up 2 notches and the a/f screw to 4.0 turns and it runs like a champ now.

[ a/f is on tight, and choke o-rings are good.

Great information Mars!!!

Littlebus: Are you saying the the air flow screw is turned in all the way tight? if so then you adjust it outat least 1.5 turns depending on how the bike runs. ensure that each jetting change you make you are using a clean spark plug. Something you might consider it the Jet4Power system. I have a link of the system in the tech section. scope it out, I run it on my YFZ 

When I say a/f is tight it means Air Filter. Air fuel screw is 3.5 turns.

If I am getting a little to much fuel at an idle but not at wot how would I fix that? a/f screw is 3.5 turns.

Littlebus,
 Back up a few steps.
1. Your air filter and intake must have a good seal. Go there first.

2.Make sure your "choke" plunger has a good seal.(o-rings)

3.Pull your spark plug see what it looks like.

4.You need a 150~165 main for a Yoshi. But you must know who made the jet you installed. Some brands use hole size and some use flow rate for sizing. Your air screw only affects idle.
I have yet to see a stock bore/cam/carb 400 need a larger low speed jet.
 It is possible you got some trash in the idle/low speed carb circiuts when you replaced the main hance the poor idle/low speed performance.

PS. ASE double master and EVT cert. I still get stumped once in a while.
 

I am running a dyno jet kit, I cleaned the carb out very well when I had it off the bike so im sure there is no crap in it, a/f is on tight, and choke o-rings are good.

A 160 is richer right? If it is falling on its face at low rpm's wouldnt that indicate that it is to rich or are 4 wheelers diff? What should i adjust the a/f screw to? Thanks for all the help guys.

It was breaking up and poping out of the intake. I am an ase certified mechanic and I couldnt even tell if it was rich or lean. I think it is rich but im not sure. If I move my pin down a notch what will that do?

Ok I just got done messin with it for the first time in a few days and I took it for a ride. It idles like sh*t at first but then I kept reving it up till it sounded like it cleared out and i dumped the clutch and off we went. This thing was like a whole diff machine but then when i slowed down to turn it ran like sh*t and had no power at low rpm's. As soon as I took off and got up in the rpm's it was like a raped ape again. Maybe it is flooding itself? Should I change the a/f screw adjustment. I got it at 3.5 turns now.I just need some low end on this thing now and ill be golden.

I got a 03 LTZ 400 and recently I put a k&n filter on it and it ran like sh*t after I installed it. I talked to a few people and they told me I need a jet kit. I got a jet kit and put in a 150 main jet. Now the bike runs like complete sh*t. Before I did the jet kit I could ride it but when I floored it it would break up in high rpm's. Now it is unrideable. For my mods and elevation I am pretty sure I have the right jet in there. I have a yoshimira slip on, Homemade K&N filter, cut up air box with no lid. If I posted this in the wrong section im sorry but didnt know where else to put it. Thanks for any help you guys can give.

I ride in the marshy mud in the hollylands and dont have any problem getting through it. Actualy I get through better then most of my freinds cause mine is so light and when i get stuck all I got to do is hit the reverse knob and back out while they are getting down in the mudd to pull there tanks out. The bombader (sp?) is a tank. It is fast but when it gets stuck that pregnant dog sinks. What is my hp stock? I dont know if any of you know him but the shee is Ronnie Wilsons. He drive a renegade mustang that runs 7's. The banshee went 7.60 in the 8th and the bomb went 8.20. What I like about mine is I have reverse and electric start and after rideing all day in the mud im not about to split my fingers open pullin some cord or kick start this pregnant dog everytime I stall. I was right next to a stock shee with just a slip on but I need to go faster. My bike is like new and has about 5 hours on it but I may sell it for a better bike if I have to.

I am wondering how fast I can get this bike or if I should sell it and buy a diff 1. I have a few freinds with banshees and some other bikes that are pretty fast but im not sure what mine will take. I found a 455 big boar kit I am looking at. A few thing I was thinking of doing are Big boar kit, Edelbrock carb, CDI box, K&N, and the hot cam kit all at once. I have a yosh slip on and have to but the header but I am not sure if all this is worth it. I am looking for a fast 4 stroke cause I ride in the dirt at the hollylands and every 2 stroke I see there is blowing up or over heating. My freind Johns bombader? made 49 hp at the rear wheels on the dyno yesterday and ronnies banshee made 75. Is there any way to keep up with that banshe? Thanks for any info.

Nevermind. I just read in another thread it is not allowed but ride at ur own risk.

I went out to the corner of Jog and Belvedere and it was awsome. I had a blast and there were like 40 other bikes and quads there. Killer whoops and trails and jumps. I am told that florida wildlife officers come out and thell ya to leave and may give a warning and tell you never to come back but all the guys out there said no1 has ever been areested. I am trying to find the owner of the land to get permission to go there. If i get ahold of him and get an ok I will let u all know. If u want to go there before that when u get to Jog and Belvedere you have to enter at the top of the bridge on Jog. U will see 2 open spots in the guard rail and i use the north opening.