Mercury 7.5 hp- fuel or water pump issue?

[brightize]

I've seen this addressed several times elsewhere, but here's the issue...Last time out with boat last year, older Merc 7.5 stalled at full throttle. Restart and it happens several more times. We used the trolling motor after that. A couple weeks prior, the prop hit a rock and killed motor. Restarted, and no issues that day. Can the rock incident be related to the stalling? Btw...motor runs fine at home in a can with no load.
From what I've read, some people think it's fuel/fuel pump related. I've also read of several people replacing fuel pump and having the same issues. Based on other online "experts" it's water pump.
The ice will be coming out soon and I need to diagnose and repair. Opinions please.

 

[racerone]

The bulb on the hose is nothing but a manual fuel pump.-----------If motor runs nicely when you operate that then the fuel pump on the motor is suspect.--------And on that particular motor the water pump impeller should be replaced about every 2 years.-------Most important if motor is pumping cold water !

 

[galamb]

The water pump may have it's own issues if it hasn't been regularly serviced, but unless it is totally shot and the motor stalled because of a severe overheat, which essentially stopped the pistons dead in the cylinders, then it would not cause a stall at full throttle.

A full throttle stall would be caused by either a lack of fuel or loss of spark (unless, as stated, the hard parts were stopped dead in motion due to being welded in the cylinder - which would prevent a restart).

Running fine "without" a load, but stalling later is "usually" indicative of a fuel issue - sometimes the fuel pump and sometimes blockages/issues with the carb.

Depending on your exact model year and the carb in use, a repair kit that will allow a rebuild of the carb and fuel pump is available for about 50 bucks. That kit and a Seloc's manual will walk you through the process of rehabbing both the carb/fuel pump and is probably well worth it.

These are great little motors that usually have few major issues, they just need to be cared for once in a while.

Do also, minimally, replace the impeller plus any gaskets or seals in the waterpump unit that look suspect. While a full blown water pump kit can go upwards of 75 bucks (depending on model year) that cost is insignificant in comparison to the price of a new motor.

If it has never had a "kit" as far as you know (or can't remember how far back that was) I would go that route. If it is "recent" then an impeller may be all that is in order.

I have a couple of portables that are about 30 years old and a third not far behind that run as well or better than the day they came from the factory. Spend a few bucks every few years and these will last for just about ever.

While you are at it, a pair of new spark plugs wouldn't hurt either. For the cost I don't even piddle around with them. New set every second year...