Quote Originally Posted by rspears View Post
A note on Thermostats. You're in WI so I'd say you should be running at least a 160F or 170F thermostat. The reason for a 140/150F is for running in salt water, where salt starts crystallizing out at around 180F, so hot spots in the heads can lead to plugging, and 140 to 150F operating temperature is right for ocean running. You've got the biggest radiator there is, so your T-stat's job is to keep the engine warm.

You said you built this engine. Has it EVER run right when warm, or is this an initial startup issue? I like Mike's suggestion of checking voltage at the coil when it's "chugging", and 36 sedan's suggestion to check grounds. Boats are terrible for corrosion, especially galvanic from copper/brass on aluminum or steel.

Also, if it's been backfiring you've likely got a blown power valve in the carb, but find the reason for the backfiring before you change it, or else buy a dozen.
This issue began from the beginning. Thats when I had the edelbrock carb on it. I switched to the stock Rochester and it solved it until I put it in the lake. Thats also why I'm questioning if I messed up the adjustments on the rockers or something since I can't really adjust it while running because of the exhaust manifolds. Im going to take a can of stating fluid with me to spray around and see if there are vaccum leaks. I will get a different tstat for it and check the voltage at the coil when its having the issue if i have time to take it out today. And I'll clean all the ground connections. Seems like if it was bad ground it would do it whether cold or hot?