Cap and Rotor have seen better days (ie, they look TERRIBLE). Hoping that's the problem, try to get out on it this week to see if it helps.

I had the same setup only with the 250's.
It seems the Merc Tbolt ignition would from time to time, fart and retard the crap out of the timing and backfire. I could hear a stumble below 2000RPM, but a backfire over 4000. I swapped the port module with the strbrd one and the problem went with the module, then module went into garbage.
Also, are you boost referencing the power valve or just over jetting? If not mapped right with your timing, you could get some lean popping.

I had a relative new MSD cap and wires on a motor that must have had some moisture under the cap....got corroded and acted up, took a while to find since I thought they were still new.
Let us know how it goes.

magnetic pickup in dist. moisture gets to the old style mercs all the time.

It's all MSD... Distributor, Ignition, Coil and the carb is boost referenced.

Having my shop look at the carb and hope to get out on it this week with the new cap/rotor. I'll let you know how it goes...

Thanks for all the ideas, I think we're getting there.

Roller cam or flat tappet if not roller check cam sometime exchust lobes where off..take valve cover of and see if all rocker arms are moving the same amount but look at the exchust..
chuck

Men,
I just wanted to let you know I finally got some time on the boat this past weekend. Ran it pretty hard on Saturday and Sunday with no issues. Guess it was the cap & rotor. I could not believe how bad they looked when I finally worked on it.. tracking inside the cap, o-zone build-up on most of the contact points, etc.

Thanks for the all the tips. Now I'm ready to sip a beer and watch the LOTO Shootout...

Quint

Well you must be in St. Louis because it rained in Omaha Sunday.

Glad it was nothing serious. See you guys at the Shootout.

Sip? That's a new one - but seriously, glad we got that boat running good.