Check for airleaks. The intake may need an o ring, or use rtv sealant. Make sure the head is on good and tight. and try loosening your gas cap and take it for a spin and see if that helps. These gas caps tend to not vent. My old one didn't, but the one that came with my one gallon tank does. Same type caps but one i had to drill a hole in to get it to vent, the other i didn't.