I just finished breaking in and tuning my Spec 3, no problems, insane torque and power. I will have to adjust the shift point on the 3 speed to take advantage of the power curve. Easy to tune as well. It does come out of the box a bit too rich even for break in, I adjusted it 1/2 turn to the lean just to keep it running with the stock glow plug, even then it would not go over 180 degrees. Once broken in I ended up about 1 1/2 turns from factory and temps run very stable (about 230) with fantastic power. The price was easy on the wallet as well. I have heard nothing but good things about the other engines as well though. Good luck with your choice.