Howdy Folks. Great forum!
I have a 2009 250/351, top done by Bill himself about 1000 miles ago..13,500 miles on it.
When warm and idling, if I hit the throttle moderately hard and rev it there is a loud clack that comes from? Sounds like the bottom of the jugs or lower end? It doesn't do it if I goose it from a about 1750 or above, just from idle when set at about 1250 or lower. Thoughts?

 

My thought is you paid $500+ for a 351 kit, I'd call B&B and ask Bill.

 

Piston slap, it's an engine, it's going to make noise.

 

I was thinking the same, but think getting the answer "from the horse's mouth" might be best.

Don't rev the bike hard from that low idle and in addition don't lug the bike down below the good power, another good reason for talking to Bill Blue. Get his thoughts on how to work the engine. Clearly he knows his product and how it should perform. Avoid hard throttle below 2000 rpm, definitely if actually rolling along at that low rpm. The big bore may pull stronger down lower, but not that low.