I got an '03 z400 and I took it out riding today with a few hiccups. Firstly here is what I know is done to the bike:

-Stage 1 dyno-jet
-K&N air filter with holes drilled in box lid
-Stock muffler with baffle removed

I bought the quad used, so I don't know what it has been through.

Here is what happened,

It would only run right on prime, I checked all the vacuum hoses, and the petcock, so I don't really know what would cause this. When I had it set to ON, it stalled out when RPMs lowered.

But here is what really bothers me, I rode around on my buddy's '05 stock z400, and just goosing the throttle in 2nd gear was enough to get the bike to wheelie. If I did the same on mine, not only did the response of the throttle seem slower, the bike didn't even come close to rearing up. In fact, popping the clutch in 1st gear renders a very weak wheelie. But besides low end, it seems to go pretty good in top end.

Help and insight is much appreciated.

 

It may be running a little rich.Or It could need a valve adjustment. Just a suggestion.

 

Yeah the jetting could be off, did the previous owner change the gearing?

 

no, I am pretty sure the sprockets are the same 14/30 I think. If the jetting was off, how would I fix it?

 

sprockets 14/40 and if you want it jetted right find somebody with a dyno and have it jetted, IMO

 

if you could maybe find out what jets it has in it and what turn out the fuel screw is at then i'm sure we can help you . its no big deal to run on prime but you will not have a
reserve and if the float needle sticks gas will run through your carb,so shut off the fuelcock when not riding.
when mine was setup the way yours is a 142 main worked very well, but i also had the airbox lid off

 

mabey the clutch is blown you should replace the clutch

 

mabey the clutch is blown you should replace the clutch, i wouldn't bother with the pressure plate

 

i am about 95% sure this has nothing to do with the clutch

 

You need to open that carb up!!!!! Take a looky at the jets and see if it has the adjustable needle.