1989 Johnson 90 hp v4 vro

[BlueFin1700]

I have a 90 hp Johnson v4 vro. I just recently had it serviced: new head gaskets, rebuilt carbs, plugs and wires, water pump. This is an after market motor for the boat I have and the boat does have a built in fuel tank (not sure if that has anything to do with it) I made sure air was getting thru the tank which it is and fuel pump working and it is. But seems to go thru fuel very quickly and I do get some fuel in the bottom of the motor. The issue I am having is it is bogging down at wot after its a little warm then at wot it goes in and out from full power to low end with out touching the throttle. Runs perfect for about a minute when cold after that it's back and forth at wot. Does anyone know what may be causing this? The shop I had fix it doesn't has time to come to the lake with me and test it. Anything would be much appreciated and many thanks in advance!!

 

[schematic]

Re: 1989 Johnson 90 hp v4 vro

sounds like fuel starvation. try assisting the fuel pump by squeezing the primer bulb while its surging. If it improves when doing so, its fuel supply/pump related....

 

[HenryB]

Re: 1989 Johnson 90 hp v4 vro

Try an auxiliary tank if you can get your hands on one. It does sound like a starvation problem. If it runs fine on another fuel tank then your problem is with your tank.

 

[BlueFin1700]

Re: 1989 Johnson 90 hp v4 vro

Awesome thanks a lot guys! I do have a portable tank I will try that today and let you know how it goes