125 issues

[turddirter]

Hey guys, first post.
I have a brand new Lifan 125cc motorcycle engine with a mikuni 22mm carb. Whats happening is I can get it up to about 45mph in 3rd and I shift into 4th it boggs down. It looses a lot of speed, itll take me down to about 25-30mph and then it starts acting right and will catch back up to 45mph but it has a hard time getting past that but wont go above about 50. I know I probably need to tune the jets in it but I dont know if I need a new main or pilot jet because when it's happening it's at the beginning of the gear so I don't know if that is considered in the high rpms or low.
Btw this is on my jialing gl-50

 

[Rodney68]

I think that you will find it maybe the main jet and/or the needle clip position. For a 125 i would say that you need a 95 or 97 main jet and start with the needle clip in the middle groove of the needle. Its just takes a bit of time trial and error to find that sweet spot by moving the clip down for more fuel and up from the middle for less fuel. Your pilot jet should be 15 or 17.5 and set the air screw under the carby near the inlet manifold 11/2 turns out from fully in. I hope this helps you out.