I custom made a new air filter for my Baja SC50, 4 stroke 50 cc Chinaped. After I put it on, it ran really sluggish and I couldn't get it above 25. I thought it would improve my power, which I need since I live on a steep hill, but it made it worse! I figured it was running too lean with all the air it was getting, but I have no idea what size jet I should go up to. Right now the main jet is a 138 I think? Also do I need to replace any other jets. Can anyone help me with this? I really want to get out and ride!