I was thinking valve guide issue, But you said the builder checked them. How did he verify they were good? Just looking at them ?
Some people have different ways of breaking motors in. Some beat on them and some go nice and easy. I personally like to do 500 miles , with half to 3/4 throttle burst. changing freeway speed , not driving a constant 65 . Then after the 500 miles i change the oil again then anything goes.
Some people have different ways of breaking motors in. Some beat on them and some go nice and easy. I personally like to do 500 miles , with half to 3/4 throttle burst. changing freeway speed , not driving a constant 65 . Then after the 500 miles i change the oil again then anything goes.