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Won’t run on full throttle, Mercury 40 hp 2-stroke

K

K_man

New member
Hi,
I have a problem that is killing me and I will give a short background.
One day going full throttle my engine bogged down and just ran on half throttle.
I found a a hole in the fuel hose and fixed it.
I thought everything was fine until a few days later when it happened again.
I have never got the engine to run good again after that.

This is how it behaves.
Runs smooth on idle and up to half throttle.
If I give it more than half throttle it will work for 5-10 s and then it starts to lose power and runs really bad and dies after about 15s.
It can be restarted and behavies the same over and over again.

Does anyone have any suggestions on what to rule out and what to look for more?
Because I am out of ideas.
  • I have cleaned the carburator (really dissembled etc)
  • I have replaced the membranes in the fuel pump.
  • I have replaced the connections and hoses to the tank.
  • Tried pressing the primer bulb to make sure it got fuel when it dies.
  • New spark plugs.
  • Tried every tips on Youtube I could find.
  • Exact model and year is unknown.
 
Check your fuel line for an obstruction and the primer bulb for fuel flow. Some times on an old hose the inner lining breaks down and collapses when the suction of the fuel pump gets higher with increased speed
 
K_man said:
Hi,
I have a problem that is killing me and I will give a short background.
One day going full throttle my engine bogged down and just ran on half throttle.
I found a a hole in the fuel hose and fixed it.
I thought everything was fine until a few days later when it happened again.
I have never got the engine to run good again after that.

This is how it behaves.
Runs smooth on idle and up to half throttle.
If I give it more than half throttle it will work for 5-10 s and then it starts to lose power and runs really bad and dies after about 15s.
It can be restarted and behavies the same over and over again.

Does anyone have any suggestions on what to rule out and what to look for more?
Because I am out of ideas.
  • I have cleaned the carburator (really dissembled etc)
  • I have replaced the membranes in the fuel pump.
  • I have replaced the connections and hoses to the tank.
  • Tried pressing the primer bulb to make sure it got fuel when it dies.
  • New spark plugs.
  • Tried every tips on Youtube I could find.
  • Exact model and year is unknown.
Click to expand...
I had a similar problem on my Mercury 60/45 jet and did similar repairs. finally after more time than I want to admit I stumbled on to a forum that recommended disconnecting the black/yellow wire from the rev limiter and try running it but not wot because it could damage the engine. Viola it ran like a champ and needs a rev limiter. In your case it could be a cdi or switchbox depending on your motor but this may just put you on the right track.
 
Motors need a new water pump impeller about every 5 years.-----May have overheated.---Sounds like fuel sypply issue.-----Perhaps test run with another tank and hose.-----Start with posting the compression numbers here.----Exhaust tuner could be partially blocked.----Post pictures of this motor ?-----A 2 cylinder or 4 cylinder ?
 
Thorny----Start a new thread and post information on your motor.-------Either solved or they bought a new motor.----Very typical.--------New motors are a good way to solve issues with older motors.----Repair shops are few and far between that work on older motors.
 
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