I bought a 2001 400ex, previous owner messed with everything, and didn't know what he was doing. I have gone through the whole quad, the quad is runs great until I put the air box on with NO air filter. When I put the air box on it pops when I am shifting through the gears and does not run as smooth. I put a stock carb re-build kit in it, and changed the jets, to a main 152 and pilot 40, bc it has a full white brothers exaust.
ANY SUGGESTIONS????
Thanks

Bob
deansremodeling@yahoo.com

 

Take the air mixture screw out a 1/2 a turn to 1 turn.
You may have to richen up the main jet also.

 

i am at 2 1/4 turns out now should i go another 1/2 turn

 

i was thinking tonight that right now i am set at the 3 grove on the needle, if i lowered the needle and restricked the fuel would that be right. right now with the air box out it runs good ( no restriction). put air box in witch ads restictiong ( less air less fuel) Dose this sould right or am i way off.

 

Pull the choke on about 1/4 of the way on and take it for a ride. If the symptoms stop you need to fatten up the mixture.

 

there is no choke on the bike yhe prio owner removed it. also what dose fatten up the mixture mean. and thanks for all your help.

 

If the carb is that messed up it's probably best to buy a new one or a good used one. Who knows what the old owner did to it?

If means you need to give the engine more fuel with a bigger main jet.

 

actually removing the choke is a very common mod...it helps throttle response to be faster. However, you need to run a 42 pilot jet in order to avoid hard starting with this mod. Also depending on your elevation, if you have this fully piped and are running without an airbox you should be running at least a 155(probably more) for a main jet(needle on the third groove)...i'm running 160 right now as I just went to Florence and that is at sea level, but I will switch it back to 158 for my normal trail riding at 3000 to 6000 feet. I have a 2004 400ex with the choke removed, a lexx slip on(not a full pipe), and a k&n with no airbox so I know what your dealing with here. Good luck

 

thanks for the help, im going to try this tomarrow. i have a 158 main so i will try that and see if it makes a difference.

 

Ok i've tried a 158 main and the bike ran real bad so i got a 155 main and tried all the setting on the needle and played with the screw on all of them as well. The best i can get it to run is the 152 main on the 3rd grove with the screw at 3 1/4.what is happening is when you go through the gears at high rpms right before you shift, its almost like you run out of gas for a second then theres gas then no gas agin. my flote has no adjustment or i would think that was it. i've never seen a 4 stroke this sensitive, is this common with keaon carbs