Mercury 650 with fuel pump or Carb issues

[Telemanblue]

Hello my name is Rod and I have an Mercury 650 outboard that I am having issues with the fuel delivery on. About the motor.... it is an older I think pre 70 65 hp long shaft. 4 Cyl and the sn is 2999744. It spent the previous 5 years on its side in a field and I have done very little to it to this point. I put it on my old boat, made sure the cylinders were oiled hooked it to a battery and fuel and it ran like a dream. I had taken the boat out about 6 times when the motor would run great then run out of fuel. I could prime the primer bulb and it would run great again until the primed fuel would run out. So I assumed it was the fuel pump. I purchased a fuel pump kit and rebuilt the pump and test ran it at home. The motor once again was running like a dream. I took it to the river and went fishing and was in love with this old motor again. Then on the second trip out since the rebuild the problem started again. It will run when I prime it then runs out of gas. In fact the other day I had to have one hand on the primer bulb and one on the wheel to get back in. Now that I have rebuilt the pump I feel that I have to turn my attention to the carbs but before I do I wanted to check with all you experts on here. The tank is a new tank so I know that part is good. The fuel lines on the motor could stand to be replace as they are old and appear to be cracked however they do not leak fuel. My thought is this... that the floats are the older style and once subjected to fuel they simply dont work right. But this is where my confusion is... if they are saturated with fuel and not floating like they should.. .shouldnt the motor actually get too much fuel?

I dont want to waste time or money trying to chase this problem down and hope to get some good advise on this old gem. The only thing that makes any sense to me is the floats but that in itself is playing with my mind. Any ideas?

 

[moorecomp]

Re: Mercury 650 with fuel pump or Carb issues

I would replace all of the rubber lines on the motor. There are 2 fuel pumps on this motor, did you rebuild both of them?. Also did you replace the check valves in the fuel pumps or just the diaphrams? A bad check valve in a fuel pump would give symptoms like this.

Craig Moore
Mancelona, MI

 

[Fuzzytbay]

Re: Mercury 650 with fuel pump or Carb issues

There is a leak, or a bad check valve somewhere. I'd be looking at the fuel pumps first,hard to belive the carbs are ok after sitting, yet seeming to lose prime would not be an expected problem (I'd rebuild them while your there). If the pumps are ok, double check the primer bulb, cheap ones can bugger up even brand new. IF the bulb is good,and the pumps are, then all thats left, is a leak. Look hard at those fuel lines, if there is a crack there maybe a leak, check the fittings too. Last but not least, the lines coming out of the crankcase, make sure they are not cracked either. These repairs are relativly inexpensive, I'd guess the motor runs good enough to invest a 100 bucks, thats about all it should cost. If you really want to know, do a compression test. If its bad, then skip it, and part the old girl out.

 

[Telemanblue]

Re: Mercury 650 with fuel pump or Carb issues

I believe I found it. I checked through the old posts on here and found one about air in the lines. Upon investigating last night I could see that there was a very loose connection on the hose and tightened it up. Seems to be fixed but only a river test will tell the truth. I did however let it run with the fast idle adjustment last night and seemed to work great! Thanks for all the help and insight. I will post a follow up on this issue and let you all know what I found out.

Yes I agree its hard to believe that the carbs are ok after setting like this but seem to be great. This winter I plan to rebuild the carbs and find a new internal wiring harness as the wires are pretty rough. Any Ideas out ther where to find a wiring harness?

 

[Telemanblue]

Re: Mercury 650 with fuel pump or Carb issues

P.S. Just a follow up... I see that there is a place for a second fuel pump but this motor actually only has one. Doesnt seem to bother the old girl though.

 

[redoakdude357]

Re: Mercury 650 with fuel pump or Carb issues

I believe I found it. I checked through the old posts on here and found one about air in the lines. Upon investigating last night I could see that there was a very loose connection on the hose and tightened it up. Seems to be fixed but only a river test will tell the truth. I did however let it run with the fast idle adjustment last night and seemed to work great! Thanks for all the help and insight. I will post a follow up on this issue and let you all know what I found out.

Yes I agree its hard to believe that the carbs are ok after setting like this but seem to be great. This winter I plan to rebuild the carbs and find a new internal wiring harness as the wires are pretty rough. Any Ideas out ther where to find a wiring harness?

I have a 1971 model 650 and I got my wiring harness from BOATS.net. Hope that helps!

 

[redoakdude357]

Re: Mercury 650 with fuel pump or Carb issues

On the wiring harness you are trying to find I have a 1971 650 and I got my harness plus a bunch of other parts from BOATS.net not much money and quick shipping.