I don't know all this is starting scare me. I ran a STS last year and it worked great til I threw a rod. I thought I would give them another try this year with the new D5 but it doesn't sound much better. My friend and I both got the D5 and he said his carb was also gritty and didn't run fer S@$t! Now I'm going to run my old carb or a different motor. I didn't even break it in yet and don't want to if I have to fix it after.