If your not getting full advance until nearly 4000 rpm I would suggest getting an assortment of advance springs and try to get full advance by 3000. If I remember correctly You'll need to have someone with a distributor machine adjust the total mechanical advance. 18 initial is a little high and 18 mechanical is a little low.
Damn, it needs a machine for that?

I'll stick with it the way it is until I can get that MSD 6AL fixed.
Rod
If it ran fine at first, that brown crap came from one of your tanks! Go to a parts store or your garage and get one of those clear glass or clear plastic fuel filters, hook it up to the fuel line that fed the carb than run a piece of hose from the filter back into one of the tanks through the filler cap. Turn on the fuel pump and let it run while you watch the filter for anymore of that brown crap. Also lift the front of the trailer a few times to slosh the fuel around a little than leave it slightly high (like the boat was in the water) and let it sit for a while first, that should put any more crap at the tanks pickups.
If you find more of it, I would pull the tanks out and flush them out realy good ! Its better than being stuck in the middle of the lake in a low profile boat that wont run because the carb is half full of brown crap!!
Been there, Done that! 
There's no way to explain it short version, so here it goes...
When I first used the carb, directly after it got rebuilt by a carb guy, I put it in my Rogers. I used it for 23 minutes in that boat. I hooked it up with used fuel line, used fuel filter, a new fuel pump, and a new fuel regulator. The sequence was: gas tanks, a "T", fuel pump, fuel filter, fuel regulator, carb. When BKPlesh was installing my fuel system in the Mach 1 (2 1/2 months later) he, and others, were giving me shit for putting the fuel filter
after the fuel pump so he switched it and made it right. We used the same filter and lines. More than likely, the fuel filter was bad from it's used begining, also likely is there was crap stuck in the fuel pump since there was no fuel filter before it. Now, the sequence is: gas tanks, a "T", a new fuel filter (glass), fuel pump, fuel regulator, and carb. I'm going to waiste some gas and flush the crap out of what's in there. The old fuel filter was a semi-clear plastic one with what looks like paper inside, the paer probably deteriorated from sitting around dry several times after it got fuel to it several times, dried out again, etc... Whew...
It's a damn good thing I saved that 3 bucks on a new fuel filter because now all I have to do is rebuild the carb, again.
