70 hp Yamaha wont open up at full throttle

[SalmonSlayerr]

Hello, Yesterday I took the boat out and after I lunched her and warmed her up for about 3 mins i left the dock and headed out gradually bringing her up to full throttle. we cruised at full throttle about 30 seconds and she just rapidly slowed t almost a complete stop. the motor did not die but at full open throttle the boat would only go about 10 mph if that. the rpms were around 2000. does anyone know what could cause this? also I only had 1/8 of a tank of gas in a 18 gallon tank. It was not back firing and idled fine. Could i have beeen sucking air? the tank is only 3 months old, the gas was also about 3 months old but i added stabil to it.

 

[Monte1961]

Re: 70 hp Yamaha wont open up at full throttle

What comes to mind is weak fuel pump or plugged high speed jet/s!

 

[99yam40]

Re: 70 hp Yamaha wont open up at full throttle

Yes it could have been sucking air,
do you know how far you can run the tank down before you run out of fuel?

3 month old fuel sitting in an all most empty tank will suck up lots of air along with moisture with it and contaminate the fuel as it breaths with temperature changes. I would look at some of it to see what it looks and smells like before adding more to it

 

[SalmonSlayerr]

Re: 70 hp Yamaha wont open up at full throttle

It is a new tank and I never ran it this low b4 but I do know Iwill never again. I plan on siphoning out the remaining gas and putting fresh gas in. I do have a fuel/water seperator... I will keep you guys posted on my prgress. thanks for anyone and everyones help.

 

[SalmonSlayerr]

Re: 70 hp Yamaha wont open up at full throttle

Hello, Yesterday I took the boat out and after I lunched her and warmed her up for about 3 mins i left the dock and headed out gradually bringing her up to full throttle. we cruised at full throttle about 30 seconds and she just rapidly slowed t almost a complete stop. the motor did not die but at full open throttle the boat would only go about 10 mph if that. the rpms were around 2000. does anyone know what could cause this? also I only had 1/8 of a tank of gas in a 18 gallon tank. It was not back firing and idled fine. Could i have beeen sucking air? the tank is only 3 months old, the gas was also about 3 months old but i added stabil to it.

I got it running perfect again. I rebuilt my carbs and bought a new fuel pump and also replaced the primer bulb & hose. Thanks for everyones help and hope this will help anyone else with similar issues.