Mercury 20 hp Stalling at full throttle

[matt73]

My 20 horse 2 stroke just started stalling out a 3/4 to full throttle.


all info I have:

1. it runs great a idle to slow
2. It will run at full speed if I pull the choke out
3. the Ball in the gas line seems to stay firm

Thanks for any help, it is very much appreciated..

[PITBULL]

Check the vent on the tank and make sure it is open and not plugged.
Also check the fuel filter. Mine is a 115 on that one the filter is a screen that is in the fuel pump housing. Im not sure about the 20 hp.
Check the fuel lines from the tank see is any are soft (they could become pinched shut on wide open throttle)
This may be a longshot but I had the fuel pump replaced and all three carbs rebuilt and had problem afterwards what happened was some debris from the fuel pump gasket had worked its way threw the fuel line and into the needle and seat on the middle carb blocking the inlet. you could accelerate fine for a minuite or so then it would bog down and almost quit. That I would think would be quite rare. And it was only after rebuilding the carbs and fuel pump.

The last thing could be a bad crank seal allowing a vacuume leak at full rpm this would affect the fuel pump since it operates off of crank case vacuume/pressure.

If you suspect the seal I would take it in and have them diagnose it to make sure it is not something else.
Try to PM Tonga.

[Burksee]

By closing the choke your increasing the vacume within the engine and also reducing the air intake.

The way your describing your condition a couple of things come to mind. All having to do with some sort of restriction somewhere after the fuel tank. And although a leaky/bad crank seal can cause this there are usually other symptom that go along with that type of failure.

I would first check:
1) Fuel Filter.
2) Float needle sticking/binding or has something stuck in it causing a restriction. Anything in the float bowl will cause problems.

Other things to check/look at:
1) Weak fuel pump.
2) Lack of vacume to fuel pump. Cracked or collapsed vacume line/hose to the fuel pump.

If it were a problem with the vent on the tank, or a problem inside the tank causing a restriction you would normally see the pump ball colapse. Another thought would be to check the fuel line after the bulb, between the ball and the engine. I have seen internal break downs of that hose (*fuel line is sometimes made from layers.) thats not visable by looking at the outside of the hose. Take it off and see if you can blow through it clearly and effortlessly. I dont think what you have is going to be anything serious but could play heck trying to find.

Good luck!

[matt73]

I think I got it fixed guys thanks a ton. I cleaned the carb, replaced the connection from the gas line to the motor and cleaned the fuel filter. Took it out yesterday morning and it ran great.


Thanks again for help.

[wildcoy73]

hey matt the problem you described is in the carb the carb works on sevral system one for idle, acceleration; and running. run some carb cleaner threw it and should fix the problem