I have a 2005 LTZ 400 equipped with a DMC Alien slip on pipe. It ran pretty good the first couple times I took it out, but lately, it runs really ratty at partial throttle openings. Pops, spits, hesitates, etc. It runs strong at anything over 1/2 throttle. I have no idea what jets are in it or what position the needle is set at. It has a K&N type air filter on it also. I assume it's carb related, these CDI's seem pretty bulletproof. I'm goimg to remove the carb this weekend to make sure it's not full of crud and to clean it. Any ideas as to where to start with the jetting / needle?

 

CDIs are not bulletproof have had one go bad on my Z. Popping and spitting are signs of vacuum leaks and that carb needs good vacuum. the slide and fuel petcock rely on vacuum to operate. spray carb or brake cleaner on hoses and carb and see if rpms raise if they do around top of carb chk the diaphram for the slider if leak is there and diaphram is ok try putting lite grease where diaphram sits. good luck

 

also would be wise to rejet carb

 

Welcome to the forums.

Easier to post the link, it will explain the throttle and which parts affect what.

 

Mine was kind of acting like that this weekend. It ended up being a clogged pilot jet. It wouldn't idle either.