i have had the carbs redone, tank cleaned, compression checked, new plugs, bulb and fuel lines and a new fuel pump. my problem is my engine is shutting off on me after a few hundred yards of running. i put the ears on the engine in the backyard and the engine runs perfect at all rpms for as long as i run it. when i put the boat in the water under normal operating conditions, it shuts off after a short time, then takes a very long time before it will start back. when i first got the boat, it would only do it every now and then and has only became worse over time. there have been some days i could run all day with no problem and then the next trip it would act up all day. any suggestion are greatly apprciated.
I would check the fuel pump/fuel supply since your problem is only hapening under load.
Last summer my fathers boat was doing something similar, up to 3/4 throttle all was fine and past that the engine would starve for gas and stall. Pump the bubble up and go again. In time it got that you could not get over 1/2 throttle.
His fuel line was colapsing on itself and closing off the fuel completely when there was to much demand for fuel.
A probleme that had me stumped for a weekend was solved by cutting off 1" of fuel line.
I hope yours is something just as simple.
edit: I just re-read your post, you have all new fuel lines?
When you say it takes a long time to restart, do you mean it has to crank a long time before it decides to fire up or do you have to let it sit for 5-10 minutes or whatever before it will start back up. If it's the later it's more likely spark related.
I would check spark related in that case.
If you do take the chance of going out with it again, be ready to check for spark when it quits.
A friend of mine had a merc that would quit after a few hours of running and it turned out being corosion in the key switch in the controls.
If he unpluged the controls wireing harness from the engine after start up it could run all day.
Any mechanic will tell you that the worst problem to solve are intermittent problems - as you are having. The first thing you need to do before you start chasing your tail is to determing if it is a fuel problem or an electrical problem. When the motor dies, does it die as if someone just shut the key off OR does it sputter, lose power, go to idle, then die. Answer that and you are half way there. (electrical or fuel)
You say that it will run all day long on the muffs, only run a few hundred yards on the water, and sometimes all day on the water. That tells me that something is shaking the boat either grounding out the ignition circuit or opening the ignition circuit (bad connection). A bad kill switch might be your first place to start. Look at it now before doing anything else and see if it is just partially tripped, not fully clipped in, etc. A bad key switch might be another culprit - not making connection all of the time internally. If you can get it to die, have a test light / volt meter handy and see if you have voltage to and from the key switch when it won't start.
You said that "i try to start it and it just turns over but no start up. and it also takes quiet a while before it will turn over and run again" A little confused here.... Will it crank without starting or when you turn the key... nothing?? If it won't crank, then look again at your key switch OR starter solenoid.
Try starting it on muffs and physically moving every wire you can in the electrical circuit. My guess it is just a bad connection somewhere - open or ground.
Probably an ignition issue. Weak ignition components tend to fail once the engine heats up to normal operating temps. The engine may not heat up to normal temps when running on a supply of cold household water. Next time you take the engine to the lake, take an inductive timing light with you. Run the engine till it craps out, then check each spark plug wire for spark. The flashes from the gun will show misfires, weak firing and nofires.
the last time i took it out, it started and i ran about 300 yards and it died. it dies as if the key was suddenly turned off. then when i turn the key to start again it turns over but wont kick in and start up. then it took about 3 hrs before it started again but then died.