Xr 400 cc motor on go kart

[marcg]

i had a xr 400 cc motor bike motor on a go kart i had it upgraded this with a 600 and now it doesnt want to run it has the same wiring setup as the other motor?

 

[Kaptain Krunch]

your being very vague, does it have spark?

You need three main things to run, fuel spark, and compression. which one is missing?