Been fighting this thing for a year now. 260 Mercruiser with old alpha drive. 350 chevy with comp marine cam (460 lift), edlebrock performer intake, 650 spreadbore marine holley, roller tip rockers, stock exhaust. Thing runs like a dream until the back barrels open then it overheats, it is almost as if the throttle is connected to the temp gauge. Even with the changes I cant get anymore rpm or speed using the exact same prop. Also, end of last summer, stopped and picked up 3 friends, so its 4 adults, 1 kid and my cooler with refreshment and could not get it on plane, it was a dog and overheated. Tore it down again this winter, nothing to explain it. Cam degreed perfectly, no visible leaks in any gaskets. Only thing funny I found was the intake, the runners off the right side of the manifold had soot at the heads, the runners off the left side were clean. I'm starting to believe this brand new Holley carb is crap. Talked to Holley about it, basically there is nothing I can do to it. I think now it is leaning out when the back barrels open. Now I think I will replace it with an Edelbrock marine carb but I'm confused here too. Edelbrock says use the 600 cfm, Crockett from the mag says use a 750, (there was a question a couple of months ago and I thought the guy was describing my engine). Any thoughts?