1983 Mercruiser 260 bogs after running 15 mins from 3200 rpm to 2000 rpm?

I am a Finlander here in beautiful Wisconsin! Bought an older Carver Santa Cruz 26 (1983) and restored it with care to it's original beauty! I love the style and size of the boat for two of us (me and my wife) boating the weekends. Anyway, I have had problems with the engine, from the time the SkipperBuds took it off and serviced drive and lower unit seal. The engine starts and runs perfect without load, but under load we get it up to 3200 rpm for about 15 minutes and then it starts to bog down? Eventually the rpm lowers to 2000 - 2200 and engine starts to run rough?
There has been a lot of investigation done to it, for finding out the cause, by marine technicians and nothing seems to help?
I am not looking for any obvious answers, like bad, or water in gas, vacuum in tank, siphon plugged, etc. The problem seems to be something, related to engine warming up and loosing the ignition on all 8 cylinders? Also, the trim adjustment effects the ignition, as I trim it up , or down from the fly bridge the engine sputters, every time?
Please help, as this is the most build engine (probably in the world), this problem is just getting so annoying, with two years on water, without getting it running as it should?

Click here to post comments

Join in and write your own page! It's easy to do. How? Simply click here to return to Mercury Forum.