70 hp Johnson power loss

[wasteman]

Motor (#39481170MX2DJ, only number I can find)has had new rings, new water pump, rebuilt the carbs, new fuel filter, new spark plugs, and new plug wires. Motor starts & idles great. After 5-10 minutes at full throttle, motor will slowly start slowing down to where it has little power. Wait awhile and motor will take off again. Do not know the year or model of this motor. Any ideas as to what could be causing this problem?

 

[Steve135]

Re: 70 hp Johnson power loss

Have you checked the ball in the fuel hose when this happens? It sounds to me as if there is lack of venting at your fuel tank and its sucking the tank till it can't suck any more fuel! Then after waiting its able to redraw fuel. Try to run with the fill either open or nearly open and see if it still happens.<br />steve

 

[Bass Runner]

Re: 70 hp Johnson power loss

Welcome to the forum, like stinky2 says check the vent on the tank, if you are using a cheap primer bulb it might be going south on you, what fuel mix are you using? If it's a new overhaul you need to run extra oil in the mix, try with two in the boat when it trys to die or loose power pumping the primer bulb if it takes off its the fuel pump giving up, check the filter on the fuel pump, it might have trash in it also check fuel lines and the tank might have trash in it. Look on the motor mount it should have a plate on it with the ser. and mod. no on it. My 70hp model no. is 70ESL74M

 

[wasteman]

Re: 70 hp Johnson power loss

The fuel pump is brand new also using a 50-1 mix i plan to try and take boat out this weekend and try your suggestions get back with after the test