[L.Holman]

So you have a YX 160 cylinder head on a 143cc big bore kit? If this is correct, then you may have issues. I did a 55mm stroker on my 2003 DR-z 110 with the YX 160 cylinder sleeve and head with a VM26 Mukuni carburetor. Try using a comp piston with the build. that fixed some issues with mine. Another issue could be the carburetor, if you're using a cheap Chinese VM26 then that is more than likely the problem. I started my build with a cheap VM26mm E-Bay special and had nothing but performance issues till I ordered the Mukuni VM 26mm from TBoltusa.com. I also had to use a comp piston for the higher combustion. The YX160 cylinder head is the same as the V1 rase head.