1 st off running 4-5 min wot is going to be rough on parts !! period, so you better make sure you have some good parts in there..valves better some real quality race types, also you timing is fine..what is fine ? working on a simular set-up in my boat...timing should be 28 total, about 15-18 initial, so you need a distributor that you can limit the advance curve, I run a mallory unilite and it's very easy to adj. also have you ever done a plug ck for jetting ?? could have leaned out, and yes the carb needs to be boost referenced if running a power valve(which you should) need to run a plug ck about a 3000 rpm 1 min run, ck new plugs, jet primary to you get it right, then wide open runs to ck secondary, lots of work, but there is no plug and play on this setup...Rob

Looks like valve seat was enough (about .090). ALso, rebuilt carbs were done with same jetting as previous and blower was rebuilt for the seals and still is same pulleys and about 6 lbs boost. MSD is ignition and it is/was 28 degrees total. After taking both heads off and checking them, it looks like the problem is excessive rust in the exhaust side water jackets. They were almost closed up. The engine was supposed to have been rebuilt the year before I got it, but it looks like they re-used the same heads. I probably run 50% in salt and 50% fresh and flush after every outing, or at the worst the next day. The mechanic told me that ammount of rust isn't from a 1-2 year old head.

Also, existing valves looked like they were Manley severe duty.

I'm taking the heads to a shop on Monday. I plan to replace all exhaust valves. Anyone have a good, cheap source for Inconel valves?

[QUOTE=rb79rb79rb79;2583165 the power valve which could represent 10 jet size reduction,