I just bought a Keihen 42mm carb off a 03 450r for my 03 z400. I put it on and it runs horible. It rides like a really, really slow 300ex. It also backfires alot. The jets are stock, the gas hose is connected fine. I have no idea whats wrong. Any ideas??

 

sounds like you need to rejet it. does it fall on its face if you get on it, maybe to lean?

 

I really dont see how it coul be lean when it is off a 450r? Some pople told me that I would have to jet down after gettin his carb. It doesnt really fall on its face as much as it has no acceleration and no power whatsoever throughout the entire throttle.

 

you have to big of a carb on there for a stock motor
when you hit the throttle you get to much air and the motor boggs
the 03z400 came with a 36mm carb.
with all the motor work i've done I run a 41mm carb and its all the motor can handle
toget it to work right your going to have to do a major rejet on it to get it to run right

 

i agree with mucky

 

should have known you'd know mucky,stewbing, how do you like your athena kit? i think thats what i'm prob. go with.

 

I do know alittle about carbs and motors. I was a auto mechanic for 9 years and now all I work on is diesels
and I'm learning about my quad one day at a time

 

Like others have said, it sounds like a jetting issue.
Do you have any other mods?
Try removing/installing the airbox lid and see if it runs better.

 

Ok so I threw a 160 main jet on there and it runs alot better. I still dont think its up to its full potential yet. What main jet do you all suggest with an HMF slip on and a K&N filter.?

 

Put a 165-170 in it. i have a 175 in mine and I have a few more things done to mine. about 2.5-3 turns out on the mix screw. Make sure you block off the hot start.