I have a pirahna 140 engine. I had to jet it to a 125 main before it ran correctly. Since you have a 125 try a smaller jet. I went down with the jets by two sizes at at a time until it stopped bogging. Now it runs perfect. Run the bike in top gear while giving full throttle and Kill the engine, then check the plug. If its black it's too rich, so clean the plug off reinstall and go a jet smaller and repeat until you get it running right. If it runs poorly a idle try changing your pilot jet.