1990 250DA Mercruiser Single 5.7

[Curtis Macdonald]

I recently bought this boat and have taken it out a couple of times with no issues at low to medium throttle. When I applied full power, the engine began to bog down and stumble, just like it had a timing issue. It ran extremely smooth at lower speeds, but was difficult plane out the boat.
So I took a friend out and asked him to drive while I loosened the distributor and made a slight adjustment while in motion. It helped considerably, but I would say it still wasn't perfect.
As we were headed back to the marina, running about 85% throttle, I immediately lost about half power and the engine stumbled until it died. It would not restart and made a very erratic attempt to restart. Very "jerky" when the key was turned, but wouldn't even think about running.
Considering the way it was running before I moved the timing, I have a suspicion that it has jumped time or possibly broken the timing chain or cam. A simple look for distributor rotation will determine if the cam is broken, first step.
NOW, the question......is it safe to remove the water pump on the engine while the boat is in the water?

 

[boatman37]

Can't answer the question about the water pump but the distributor runs off the camshaft so if the distributor is spinning then the timing chain is not broke. Possibility it jumped time but I would check other things first. Get a timing light and set it accurately. There should be a timing tab on the front. Set it to TDC on the compression stroke and see if the rotor is pointing at (or very close to) #1. If it is way off then it is possible it jumped.

I suspect you just got the timing too far out of whack by tuning 'by ear'. Also not a good idea because of the threat of detonation and the possibility of blowing a hole in the piston or breaking ring lands.

Check the easy things first and rule those out.

 

[Curtis Macdonald]

I'll know more when I return to Texas and have a chance to take a glance at it a little closer. I only moved the timing ever so slightly while running, I would say no more than 4 to 6 degrees max. So yes, I will check the easy things first. My biggest concern is, can I safely remove the water pump from the motor while it's in the slip in the event that I have to replace the chain set? Thanks for the advise!

 

[dlvwill]

Put locking hose pinch pliers or disconnect and plug the raw water supply hose coming from the transom plate and you can safely disconnect the rest of the cooling system.

 

[Curtis Macdonald]

Put locking hose pinch pliers or disconnect and plug the raw water supply hose coming from the transom plate and you can safely disconnect the rest of the cooling system.

Great idea. Thanks for the advise. All I have to do is locate it now. I'll use a set of needle nose vise grips and lightly apply the clamp!

 

[dlvwill]

Top of transom plate just to the starboard of centerline, about 1" diameter.

 

[BillK2632]

If you tried to time it while it was running at speed, the timing is probably all mess up. You were trying to time the engine based on the advance and not the base timing. I would guess the timing is severely retarded at this point. You need to go through the timing process for that motor. You can use an old fashion timing light, but if you put the light on it with out it in base timing mode, you will see the timing jumping all over the place, this is the advance and knock sensor adjusting the timing.

Read this: http://www.boatfix.com/merc/servmanl/16/16b4r2.pdf

 

[Curtis Macdonald]

If you tried to time it while it was running at speed, the timing is probably all mess up. You were trying to time the engine based on the advance and not the base timing. I would guess the timing is severely retarded at this point. You need to go through the timing process for that motor. You can use an old fashion timing light, but if you put the light on it with out it in base timing mode, you will see the timing jumping all over the place, this is the advance and knock sensor adjusting the timing.

Read this: http://www.boatfix.com/merc/servmanl/16/16b4r2.pdf

Got it! Thanks!!