2002 Yamaha 50 2 stroke

[Sussky77]

I have recently pruchased a 2002 triumph with a 50 HP Yamaha 2 stroke. The motor cranks and idles fine. When I first take off I will revceive full power and get up to 5400 RPM. All of the sudden it is like I loose fuel supply and the motor bogs down and I can only idle and cannot get any power. I first replaced the fuel line on this boat and placed an inline filter in the line. I also replaced the spark plugs after finding the ones in the motor were loose and only hand tight yet I am still experiencing the same problems. Any ideas on the root cause? Thanks Sussky77

[99yam40]

check to make sure your alarm system is working, maybe going into RPM reduction due to oil level or overheat and buzzer is not working

[a387673]

Fuel Supply

I had a problem with similar symptoms on a 40 HP 2 stroke. Turned out to be crud in the fuel tank from a rusted sending unit, lodging against the anti-syphon ball/spring/valve in the fuel supply line coming from the under-floor fuel tank. I used a portable tank to aid in the diagnosis. Problem went away when using the portable.

Solution was to remove the anti-syphon ball/spring, but also placed a fuel/water separator filter in the line to the engine as some of this crud was making it to the filter on the engine. Initially replaced the fuel/water separator filters at short intervals to help clean the tank. Alternative was to cut the tank out of the floor to replace.

If you can temporarily hook to and run from a portable, you can at least determine which side of the fuel connector the problem is on, engine or tank.

[a387673]

Fuel Supply

I had a problem with similar symptoms on a 40 HP 2 stroke. Turned out to be crud in the fuel tank from a rusted sending unit, lodging against the anti-syphon ball/spring/valve in the fuel supply line coming from the under-floor fuel tank. I used a portable tank to aid in the diagnosis. Problem went away when using the portable.

Solution was to remove the anti-syphon ball/spring, but also placed a fuel/water separator filter in the line to the engine as some of this crud was making it to the filter on the engine. Initially replaced the fuel/water separator filters at short intervals to help clean the tank. Alternative was to cut the tank out of the floor to replace.

If you can temporarily hook to and run from a portable, you can at least determine which side of the fuel connector the problem is on, engine or tank.

[Bilge Rat]

Start at the tank, Check for crud, old fuel, and water. The anti siphon valve in the jag that the fuel line goes on and new fuel line all the way from tank to motor.

Did you replace any filters on the motor?
Clean the carbs or injection system?

Check the alarms.

The boat is new to you, was the water pump replaced recently? Overheat can throw the motor into low RPM mode.

[robert graham]

Check your fuel tank vent....if it's turned off or plugged up, it will starve your engine for fuel and do what you describe....

[Sussky77]

This motor has a new water pump and alot of pressure through the tattle tail. I am not sure if the alarm is working or not. How would I verify if the alarm is working? Fuel tank had been emptied and cleaned by the previous owner. I did install an inline filter and new fuel line. The way it behaves and from what I have read I believe it may be ther fuel pump or carbs junked up.

[robert graham]

"Running 5400 RPM's then bogging" says fuel starvation...possibly caused by weak pump, fuel restriction or insufficient tank venting....are you sure of your tank vent?....

[robert graham]

What kind/size "in-line filter" did you add?....if your problem started After the addition of the filter, then the filter may not have sufficient flow-rate for wide open throttle....

[Bilge Rat]

If the PO cleaned the tank there was a reason. With no inline fuel filter on it before whatever was in the tank that needed cleaning out is in the motor.

Start at the tank, vent, antiisiphon, line, filters, pumps, carbs and verify they are all clean and in working order.
Check for air leaks. What gauges are installed on the boat?

Premix or oil injection?
Has the t-stats and poppit valve been checked?
Was the motor running good when you bought it?

Vent, antiisiphon, bad pumps and old fuel lines can cause your issue.

[99yam40]

This motor has a new water pump and alot of pressure through the tattle tail. I am not sure if the alarm is working or not. How would I verify if the alarm is working? Fuel tank had been emptied and cleaned by the previous owner. I did install an inline filter and new fuel line. The way it behaves and from what I have read I believe it may be ther fuel pump or carbs junked up.

Pull the clip off of the kill switch and then turn the key to start.
The motor will turn over but will not fire spark pugs so it will not start, but the buzzer should sound if it is working.

You can also ground the pink wire at the over heat temperature switch on the motor with the key in the on position that also should sound the buzzer.

If the low oil or overheat is coming in and causing RPM reduction you should be able to see the timing retarded as that is how it reduces RPM.
no power if timing is not advancing to specs

Post the full model # so we can be sure what motor you are talking about