Mercury 25 s/n 0T452701 stalling out - have to use primer bulb to keep running

[natecollins1]

Hi,

I have seen were several people on this forum have had similar problems with Mercury 25 hp 2 strokes having trouble stalling out after several minutes of running unless the primer bulb is pumped. I am having similar problems. I have cleaned and rebuit the carburetor and fuel pump. I checked all carb passages and they are clear. I rebuilt the fuel pump first with just a new gasket and diaphragm and then again with a new pump body (valves). I have changed hoses, fuel tank and fittings with no cure.

Has anyone been successful at finding a solution to this problem? It appears that the fuel pump is not pumping enough fuel, but unfortunately this fuel pump is cast into the carb and does not have a pulse line coming off the crank case to help move the diaphragm. Any answers from someone who overcame this problem would be greatly appreciated.

 

[will941s]

Re: Mercury 25 s/n 0T452701 stalling out - have to use primer bulb to keep running

Usually thats caused by air in the system somewhere. There is a pulse hole, when you took the carb off; the little hole that ran through the intake plate, through the intake gasket to the carb is the pulse hole that works the fuel pump. Did you replace the primer bulb? Make sure that the o-ring on the engine fuel filter bowl is intact, the lines are not leaking, no leaks on the carb anywhere. Also make sure the vent on your gas tank is open, and the pick up tube in the tank isnt leaking. Make sure you have the right connectors (Yamaha connections fit, but too loose). Somewhere in your system you are losing a prime and sucking air. Its like poking a hole in a straw while your drinking. Also make sure you have the carb assembled correctly and the intake to carb gasket is installed in the right position.

 

[natecollins1]

Re: Mercury 25 s/n 0T452701 stalling out - have to use primer bulb to keep running

Thanks for the tips. I inspected the fuel pump again and see the pulse passages you are talking about. That is clear. The intake gasket is positioned properly. I installed a brand new gas tank and directly connected it with a new fuel/primer line directly to the fuel pump fitting - no quick connects. The only way that I could keep the engine running was to prop the gas tank about 2 feet above the engine. I then installed a fuel filter in line and can see it getting sucked dry if the tank is lowered to its original location.

 

[Fuzzytbay]

Re: Mercury 25 s/n 0T452701 stalling out - have to use primer bulb to keep running

Just for clarfication, by fuel/primer line, did that include a prime ball pump?

 

[natecollins1]

Re: Mercury 25 s/n 0T452701 stalling out - have to use primer bulb to keep running

That includes the a fuel line with primer bulb assembly. I connected this directly between the fuel tank and fuel pump.

 

[Fuzzytbay]

Re: Mercury 25 s/n 0T452701 stalling out - have to use primer bulb to keep running

I am not familar with your motor, but it seems by a process of elimination your carb rebuild was not 100% correct, and I think maybe you should check if your float is set correctly, or doesn't really float......ie it has a leak


Had one last thought, the arrow on the ball points towards the motor....
correct?

 

[natecollins1]

Re: Mercury 25 s/n 0T452701 stalling out - have to use primer bulb to keep running

I have the OEM manual. The float is set correctly and the float is floating. This carb has been cleaned and rebuilt twice just to make sure there were no errors the first time. I checked all passages to make sure that they were clear. This is a very easy carb to rebuild. Also the primer bulb is pointing in the correct position.

I would like to hear from anyone who has actually had this same problem on their motor and figured out the solution. There are several people on the forum with the same issue, but no one ever wrote what it was that fixed their motor. Thanks for all your help.

 

[HawaiiMercury]

Re: Mercury 25 s/n 0T452701 stalling out - have to use primer bulb to keep running

Yhea, I also have the same problem. Mostly just dies at Idle then I pump the bulb and it runs fine. It has a new fuel pump an dfuel lines.

 

[rclindsay]

Re: Mercury 25 s/n 0T452701 stalling out - have to use primer bulb to keep running

This thread is old but needs an answer. My engine ran fine until it sat for several months, now stalls at WOT, idles fine. Spent the whole week fighting this. Gun it, die. Repeat several times, then Zoom. Its like an obstruction clears, then gets stopped up again. Always starts and idles fine. Also when it is running at high speed it may gradually or suddenly die. On my last attempt I squeezed the bulb tightly and it ran fine. Hate to remove the carb if there is a simpler solution. Fuel filter and lines are all clean and tight. Tried two different fuel tanks, lines, and bulbs. Same problem. Need a diagam of the fuel line components and carb diagram. There is a white bowl at the upper front that seems to be a fuel separator of filter that goes to the engine fuel filter. Fuel pump gaskets, a dried diaphragm, clogged high speed jet or float bowl are possiblities I suppose but I suspect there is probably something simpler. Will do the clear vinyl bubble test next to check for air leaks I may have missed. Hope to hear from others with more experience before wasting time with the carb. Thanks for any suggestions. Rick