1983 Mercury 50 Carb Question

[tshelton1]

I recently purchased my first boat and have been working on it to get it running nice. I have checked the compression in all 4 cylinders and they have good even pressure. The first time I took it out it ran for a few seconds and then flooded out and I had fuel pouring out he bottom carb. I suspected my float was stuck or the needle/seat needed cleaned. I took the carb off and inspected the needle and float which seemed ok so I cleaned it and put it back on. I ran it hooked to the hose for about 3 hours straight revving it up and down. During this I ran a can of seafoam thru it to help clean it out. It ran great and did not flood. I decided to take it back out and test it on the water and it ran great but when I came back to the dock I put it in neutral to drift in and it flooded out again and I had gas pouring out of the bottom carb.

I ordered a rebuild kit and new float for the carb but I got thinking today that the previous owner had a switch on the dash for a fuel pump and I have been leaving this on thinking that's how the motor got fuel but the carbs have fuel pumps on them. The carbs are model Walbro WMA-1. I believe that he may have been using the fuel pump to help start the motor and then was turning it off and the fact that I keep it on might be overpowering the spring on the needle valve thus flooding the carb.

I am new to working on boat motors so I was wondering if this made sense. I am going to test my theory when I get home.

 

[Chris1956]

Outboard motors with carbs usually do not have electric fuel pumps. I would leave the fuel pump off and see if the carb behaves.

Merc carbs need rebuilding all the time, so don't fret about rebuilding it before it needs it. Check the float. A lot of the original ones were foam and the alcohol in today's fuel was hard on them. Newer floats are hard plastic.

 

[tshelton1]

So I went home hooked the boat up to water and turned on the fuel pump started it and then killed the fuel pump. It ran well but immediately I noticed it wasn't pumping water. You know because fixing your carbs does that haha.

Anyways I let it cool off and went out stuck the hose to the pee hole thinking it may be clogged up. I put the muffs back on and started it again same issue was not pumping water but was pumping air out pretty hard.

I took the lower unit off and took the cover off of the water pump to inspect it. The impeller had nicks but all the blades were intact so I put it all back together and started it up and after about 5 seconds boom pumping water again. I shut it off and started it and now it was pumping water and running great.

I had a couple of questions.

1. Why would it have pumped air but no water and now pumps fine?

2. There were 2 rubber grommet looking things that slid off off the shaft going up to the motor. I believe they were on it for where the case got close to the shaft in 2 spots. I could not get the lower to go back on with these on the shaft so I left them off. Is that what they were for?

3. There was a small tube coming out of the very rear of the lower unit that fished up through and out a hole half way up. It appeared to be some sort of breather line but looked like it had a cap on the end. What would this be?

 

[Chris1956]

Not sure why it would pump air. Maybe flusher was not on correctly, or water pressure was low? Nicks in the impeller are troubling. That motor likely has no thermostat, and relies on max pumping to keep it cool at high speed. You might replace impeller, wearplate and two gaskets.

Not sure about the rubber grommets. There should be a thick rubber washer above the waterpump cover, on the driveshaft. That is a slinger.

Small rubber tube out of gearcase is probably speedometer pitot.

 

[tshelton1]

I found a parts diagram online. I had the slinger on at he base of the pump correctly. The other 2 are driveshaft seals, I guess to keep water off of the splines. You were correct that the one I thought was a breather was actually for the speedometer.

I took it out last night and sitting at the dock it took a few seconds but started pumping water. I drove around the dock area and the boat ran great. I was watching the water outlet and I saw it to start to sputter so I turned the boat toward the dock and then it stopped pumping water all together so I killed the motor and drifted slowly back to the dock. It was pumping air/steam out of the outlet. I'm going to go ahead and order a water pump kit and replace the impeller and those seals. As for the pumping of air I still do not have a clue why it did that. When I had the lower off the last time I used the hose to spray up the outlet tube and water came out fine.

Is it normal for it to still pump air out if the impeller or pump are bad? It may just be a little air/steam from the heat but it seamed to come out pretty good. Anybody ever have this happen to them?

 

[Chris1956]

Normally your motor would have a plastic guide tube in the waterpump cover to make sure the water tube fits into the waterpump. There is also a seal in the base of the waterpump tube outlet.