5hp 2-stroke won't idle, runs at 4000 rpm and dies if I try to throttle down or idle

[Bote Man]

My Mercury ME 5M 2-stroke starts easily, but the "start indicator" throttle position runs it at what sounds like 4000 rpm to my ears. If I throttle down, it begins to die. I don't know the engine's history much, but it was running prior to me getting it ... it has set for about a year.

1. I began with a new spark plug, NGK BPR7HS-10 as the book recommends.
2. First start was crazy high rpm, sort of got me very concerned.
3. Redid lots of stuff in the fuel system: cleaned tank out, new pickup tube.
4. The vent is open on the tank.
5. Cleaned the carb twice. Both jets removed and cleaned, cleaned all ports.
6. I tried draining the fuel bow while running.
7. I tried a test of running with fuel tank disconnected. It revved higher after a minute, so I discontinued my test.

Maybe it's the float valve or the little "fuel pump" thing that sits against the fuel bowl.

 

[Bote Man]

Here's the video for this crazy thing.

Engine won't idle

 

[Sea Rider]

Some issues :

Is it a salt or fresh water motor use ?

-Quite possible to rev at 4 K at the start indicator position which it's a very bad idea testing said motor revving that high without load, test it while running powering anything that floats at full throttle.

-Have you checked the fuel pump's diaphgram condition ? Probably in bad shape ?

-The peeing tube seems to be having prostatic issues, insert a stiff wire severel times up/down to clean it, if still with issues, the impeller is shot or the motor has internal accumulations being salt, scale whatever has collected while being run at sea, or fresh lakes, rivers, etc, or a combo of both situations.

-Has that nice small motor ever been sprayed decarbonized before through the carb with any carbon remover product ?

Happy Boating​

 

[drenzer]

My Mercury ME 5M 2-stroke starts easily, but the "start indicator" throttle position runs it at what sounds like 4000 rpm to my ears. If I throttle down, it begins to die. I don't know the engine's history much, but it was running prior to me getting it ... it has set for about a year.

1. I began with a new spark plug, NGK BPR7HS-10 as the book recommends.
2. First start was crazy high rpm, sort of got me very concerned.
3. Redid lots of stuff in the fuel system: cleaned tank out, new pickup tube.
4. The vent is open on the tank.
5. Cleaned the carb twice. Both jets removed and cleaned, cleaned all ports.
6. I tried draining the fuel bow while running.
7. I tried a test of running with fuel tank disconnected. It revved higher after a minute, so I discontinued my test.

Maybe it's the float valve or the little "fuel pump" thing that sits against the fuel bowl.

Possible vacuum leak at intake?

 

[Bote Man]

I tried an aftermarket carb kit, but didn't greatly improve. I found a cheap carb on Amazon, and it works great.