Hello, i recently picked up an 87 baja 240 with a carb'd 454 that im having some problems with. Just the other day out of the blue it starting missing bad under a load. While either taking off or at WOT in the water it misses, sometimes causing the engine to die out. It runs great at idle, or running on the hose out of the water. Another thing i noticed is that while running it in the ranges it misses, if i adjust the trim or trim tabs it feels like the whole boat is coming to a stop. The engine almost cuts all the way out. Both batteries are new and at idle they show to be charging around 13.4 volts. Engine off the test 12.5 volts.

I have replaced the stock mercury distributor cap and rotor, installed new AC plugs, and MSD plug wires. This made no difference!

If you leave the boat idle for a while and go to take off, its worse than if your running mid throttle and opening it up.

Any help is GREATLY APPRECIATED!!!!!!!!!!!!!!!!!!!!!!!!!!!

Thank you
Justin

IF you already changed plugs, wires, rotor and cap along with checking the timing, I would check the gas, (maybe old or have water in it) and carb. You should have a fuelfilter/water separater, (looks like an oil filter) remove it and pour the contents into a glass jar and look to see the condition of it. Good luck

Changed the fuel filter/separator. Fuel is not that old. Poured out the old filter and was clear as can be. Also smelled fine.

Just doesnt feel like a fuel problem to me really, its kind of weird. There is no backfiring either, just flat out misses.

Have you checked the ground on the block to make sure it is tight

And with the engine dieing out when anything electric(trim, trim tabs, etc...) is used when its missing keeps leading me more into the electrical side of things...

Have you checked the alt. with a meter you can pick one up pretty cheap at wally world think mine was $12

Good alt. will put out 14v

The ground seemed to be tight and fine on the engine. That was my initial thought with an alternator. But running it tonight in the driveway, it is charging somewhat. Again it would go to about 13.4 volts. My theory was its not quite putting out enough for the ignition side of things, and when any other current is needed its totally killing out the ignition? I may be totally wrong here, but again any help is Greatly appreciated.

Thank you!

MIne was doing almost the same thing. On plane above 3500 it wounld cut out labor then die. If i stopped it would fire right back up like nothing happend.

Fuel pump!

Sounds like you need to check fuel pressure under load. Anti-syphon valve on the gas tank may cause a problem.
Check cylinder compression.

Also inspect the possibility of the spark jumping from the high voltage tower (on the coil) to the small negative terminal on the coil. You can see this best in the dark.

Check the spark between the dist cap and the coil with a simple spark checker. You can watch it while the boat is being tested.

Dennis Moore