So I have a 2007 YZ450f I use just for the dunes. While away on a dual sport trip I had a new top-end put in because it was burning some oil. They put in new pistion,rings, gaskets, and stainless valves since my titanium ones were shot. Took it out today, fires up 1 kick but after idleing in the garage for just 2 minutes it starts to piss coolant out the overflow??? Never did this before, you could leave it running for an hour with no boil over. So I check the coolant and its still above the fins so I ride. Everytime I stop and give it a few revs within seconds out comes coolant. Its also popping upon decel like a machine gun, so its gotta be running super lean right? Only thing is last season I had it jetted and it was running great. I checked to make sure the choke and hot start are not stuck open. They didn't touch the carb so why now is there an issue. I guess my question is two fold. First is there anything they could have screwed up not including the carb to make it run the way it is? and is my engine being very lean leading to the coolant issue? or is that another problem altogether? When riding the bike pulls and seemsto have no fuel/jetting issues at all except for the popping. Please something to look for?