2001 yamaha kodiak 400 4x4 runs fin cdi box is good spark plug is good but will only run about 20 mph doesent spit or sputter runs perfect any solutions

Could be a weak spark, since a weak spark will break down under load conditions. Pull the spark plug and make sure their is a fat purple spark. It could also be an air leak between the carb and the intake manifold causing a very weak gas to air ratio, running too lean.

check conections on new parts just had that deal new cdi had one wire that pushed out just enough to lose contact. sounds strange but it happens.

Sounds like a frailed throttle cable, or that it might be rusted or mucked up with something. Would undo it on carb and see if it has full throttle movement on the cable. If you have not done this yourself before best to have it done professionally or do some read up good luck hope this helps

look for loose wires and check the resistance of the plug cap

1998 Yamaha Kodiak 400 Wiring Diagrams 2001 yamaha kodiak wiring diagram... This might help you to find the problem

It is most likely gonna be the cdi inside the motor. Those are famous for going out. It's not a bad change tho. The part is about 250 dollars and you'll need a new gasket and oil. And really that's all.

It is most likely not the stator
it is most likely the CDI box (black box) however to check the stator there are two or three yellow wires comming out of the stator check each of the wires with a ohm meter for continuity if any goes to ground the stator is bad but most likely it is the CDI box

check supp lie electricity to coil, if ok. but no spark. check ur ignite r in ur cdi box

check your pickup coil?

Yamaha ignition coils never go bad. It is probably the Stator/ Pulser coil (very common). You can check them with a ohm meter. You'll need the readings from a Yamaha dealership. The CDI box is very seldom bad But there is no checks that can be done on it. If everything else is fine ---than Yamaha says it must be the CDI box.(Rare)