I have a buddy who has a 2004 (I think) ltz400. It will idle fine and rev up like normal in neutral. When you put it in gear and start to take off, it will run, but it loses a lot of power and seems to bog down. He seems to think maybe it's his CDI box. It has a Big Gun pipe on it, but no aftermarket CDI. Could this be the problem or does it sound more air/fuel related?

 

Ask him if he re-jetted

 

yea, he has. The bike was running fine at one point. This is one of those issues that seemingly popped up "over night."

 

more than likely your going to have to ajust the fuel screw ,turning it out , you did not say what the new jetting is or what mods there are so its hard to say much more

 

Not sure about the jetting and other mods, I believe the only other thing he has is a KandN air filter. The thing is, with his pipe, etc, the pipe used to run fine. His problem didn't start occuring after the mods.

To explain the problem a bit more...in neutral the thing runs like a champ...idles...revs up...sounds great! Put it in gear and all of a sudden all that power dwindles. It will run, just not good...seems to be flooding itself out.

 

Not sure about the jetting and other mods, I believe the only other thing he has is a KandN air filter. The thing is, with his pipe, etc, the pipe used to run fine. His problem didn't start occuring after the mods.

To explain the problem a bit more...in neutral the thing runs like a champ...idles...revs up...sounds great! Put it in gear and all of a sudden all that power dwindles. It will run, just not good...seems to be flooding itself out.

 

dirty air filter will do that so will a plugged up spark arrester,engine valves can go out of adjustment to

 

He needs to take the carb out take it apart and clean it and make sure the float level adjustment is to spec, replace the jets, get rid of that dirt sucking K&N filter and replace it with a good quality sponge oiled filter, clean all the vent lines clogged with dirt, empty his gas tank out with fresh 91oc gas, install a ne spark plug. Then put it all back together and it should run fine.

 

my 05kfx400 did that same thinig last week or so. no power over half throttle in gears. i put new kn fitler i had layin around. i put carb cleaner an ran that through for an hour or so at idle then it still had a problem. i then emptied the gas an put fresh in it. i added oil cuz i was about half quart low. still acted up. then i put it away for night an when i took it out next day, shee ran fine no problems. i also took off the tps and oiiled that cuz i thought it was an electronic proib. after all those little tinkerings it worked fine next day. maybe the gunk in carb mighta got pushed through. idkk. good luck thoguh an try all the stuff i did.

 

Could also be bad gas. Is he running without the airbox lid? He's main jet should be at leat between a 165 and 170 OEM jets, not this junk jet kit. Get the OEM from the dealer for $3 a jet. make sure there is no air being sucked in from the boots on both sides of the carb. My next guess is a clogg in the carb, take her apart and blow her out! Good luck.