Hello Bill,
Welcome to the forum! We’re going to find the problems with your boat, it’s just a matter of time.
Whatever the issue, it appears to be ancillary in nature and not "main mehcanical". Many old boat owners are so rattled at ancillary malfunctions, they end up getting hooked for tens of thousands of dollars worth of repowering, when all it really is may be the need for attention to detail and careful troubleshooting.
On one of my 427s, I got a zero compression in one cylinder, because the prev owner had set the valves so poorly. He didn't know what the heck he was doing, quite frankly. Once set properly, compression came up and the motor is still running great ten (10) years later. A 427 does not like to run if the valves are set too tight. Too loose, it will run, and make lots of valve noise, without developing full power. Set right, they're just beautiful.
Sooner or later you'll want to upgrade to the PERTRONIX ignition modules, there is a dedicated thread on this, and it's simple and cheap, and the benefits over running a 427 with ignition points are immense. Many 427 owners have done this.
You’ve got a lot of issues with an engine that has not been run since 1999. Many times, we’ll see more than one gremlin working at the same time. Don’t assume it’s just one thing.
In your last comment, you said the engine overheated, missed, and died again. Question that needs to be outlined for me and the others who will want to comment, “is the overheating a normal thing, does it overheat and then stall out, or did it just overheat this particular time”? Also, what was the nature of the overheating, how hot did it get, did it make any special noises, etc.?
Also, have there been any mods to your motors? Are you running stock PCV valves, ballast resistors, and carbs? Did the boat once run well, and now is it acting up? Is this a raw water cooled motor, or do you have heat exchangers with antifreeze in the reservoir?
Are you running ballast resistors and the proper coils? If not, the coils may well be overheating and getting so hot they’re losing their ability to generate a spark and then fail. Changing to a new improper coil may just replicate the old problem. I think Dave had a good comment, when you lose power, do you actually “have” any spark? Need to know this (good comment Dave!).
Dave had another good comment, and that’s the heat induced vacuum change. It’s possible that the hot engine causes something to loosen up and admit more air below the carb somewhere in the intake system. The carb may be loose, the gasket may be admitting air under the carb.
My first guess, however, is obstruction within the fuel lines. It sounds like the engines run long enough to draw debris into an obstruction and then they choke out. Curt Hill had similar issues to yours and he found he had a lot of junk in his tanks. I have a buddy here in Nashville with a much newer boat, and he would run down the river several miles and every trip (when the engines got hot) he would stall out at the same general location. He thought it was the “Bermuda Triangle of the Cumberland”. He tried everything, but found eventually after changing out lots of parts, it was an obstruction that occurred at an anti-siphon valve in his fuel line. We old boat owners don’t have anti siphon valves, but we do have shut off valves with 90-degree bends, etc. He finally found out he could run down the river for a while until particles finally built up enough to stall out his motor. Sounds just like yours.
Someone on the forum suggested hooking a temporary test fuel line to an outboard motor fuel tank, running off it to be sure your main tanks were not the issue. Doing so would guarantee you were getting a clean and unobstructed fuel supply. I suggested to Curt, that he hook up a suction to his fuel lines and pull out whatever it was down there, to test if it was a continual fuel supply. He changed out filters, etc., but finally found lots of debris was clogging his main flow to his fuel pumps. He pulled his pick-up tubes, and siphoned out lots of debris.
I would hope Tim Toth, Mark Weller, and Curt Hill, among others, Tom, Dave, Howard, Wes, would offer their comments too to help diagnose your issues. What we need are as many symptoms as possible.
For instance, when you tried to restart, did you look into the carb (with the motor off), and pump the throttle to see if you were getting jets of fuel squirted into the carb? If so, fuel starvation probably is not the issue. If you can see fuel squirting when you run the throttles all the way forward and back, and if you’re getting a spark as Dave noted, then we’re ready to solve the problem, as there’s not a whole lot of issues left.
I would wonder if when your engine stalls out, if it would restart and run if it was given a boost with starter fluid. This is not normally such a good idea, but starter fluid will make a motor start under just about any condition, vapor lock or not. I wouldn’t recommend this, because I would satisfy my curiosity by checking for spark when the motor cuts off (as Dave recommended) and then I’d look into the carb and see if it was overly wet (over choked) and also have someone pump throttles to see if you are able to see fuel being squirted into the carb. If you see fuel being squirted, I doubt if starvation is the issue.
Fuel pumps may be suspect. Malfunctioning choke may be suspect too. When you stall out, pull the flame arrestor off, look inside, and if you see the choke butterfly closed, the heat activated choke mechanism may be malfunctioning.
Here is a thread to Curt Hill’s “sawdust in the tanks” thread.
http://www.network54.com/Forum/424840/message/1146731677
Regards, all the best, gimme some help here fellas!
Paul