94/95 Force 120 - bogs down at full throttle

[kingstretch]

I've got a 94/95 Force 120 that starts up well, idles well and runs at full throttle well... for a few minutes at least. I think I could probably idle it around all day and it would be fine, but when I run it full throttle, it runs well for about 200-300 yards and then I can feel the engine start to lose power and slow down, it will eventually just come back down off the plane and for the most part be idling again. I recently replaced the fuel pump, and I was thinking it might be bad again, but I can see the fuel level in the fuel filter (between the pump and the carbs) and it is completely full of fuel.

Not sure where to look next, any advice?

 

[bentle]

Re: 94/95 Force 120 - bogs down at full throttle

Start at the tank. Check fuel pick up tube in the tank and screen if any. Replace fuel
lines from tank to carbs. If you have a primer bulb then replace it as well. It needs to stay firm after primming. Is there any fuel leaking out of carbs? Could be the pump but try the others first and see what you get. Let us know what you find.

 

[kingstretch]

Re: 94/95 Force 120 - bogs down at full throttle

Start at the tank. Check fuel pick up tube in the tank and screen if any. Replace fuel
lines from tank to carbs. If you have a primer bulb then replace it as well. It needs to stay firm after primming. Is there any fuel leaking out of carbs? Could be the pump but try the others first and see what you get. Let us know what you find.

Thanks bentle - I probably should have included more of the maintenance I've done...

* Fuel line is new from hull fitting all the way to fuel pump - only original line is from tank to hull fitting
* Primer bulb is new (beginning of this season)
* Fuel pump has been rebuilt (beginning of this season) and screen in pump was cleaned out
* New fuel filter (see-through kind) was installed so I can see the fuel level and filter condition
* Fuel was drained and filled with fresh fuel/oil at beginning of season

The fact that the filter stays full of fuel makes me feel like the pump is doing its job and sucking fuel from the tank and pushing it through at least to the point of the filter, so I feel like I should be able to rule everything out between the tank and the filter (this may not be correct). The only thing left after the filter is fuel line, a T fitting, and the carbs. How can I tell if fuel is leaking out of the carbs? Would I literally see fuel dripping out of the mouth of the carbs?

 

[Jiggz]

Re: 94/95 Force 120 - bogs down at full throttle

A full fuel filter doesn't discount a faulty fuel pump since carbs do not suck fuel per se instead are fed with fuel by the pump. Unless, the fuel filter is located above the carb bowls where gravity will will feed the carbs. It could be the fuel pump is under-delivering fuel (due to leaks in the fuel lines) or it could be the carb floats needs to be checked for proper operation. And finally the float needle valve. After the engine slows down to a minimum, stop engine and try opening one of the carb bowls and check for fuel. Is it empty or half empty? If it is, check the float operation and also the needle valve using the primer bulb. If float and needle valve operation is OK then it's time to focus on the fuel pump. For this you will use a fuel pressure gauge, a T-fitting and a clear hose (or since you have a see-through fuel filter you can skip the clear hose). Install a T- fitting between the fuel pump outlet and the carbs. Install the fuel pressure gauge. Replace the rubber hose from the fuel pump outlet to the T-fitting with a clear hose. Now run the boat in the water without the cowl cover and go through high speed slowly while watching the fuel pressure and the clear hose. If fuel pressure is below specs, the fuel pump needs repair or replace. If fuel pressure is within specs and you see bubbles in the clear hose (or fuel filter), check for leaks in the fuel lines between the pick up tube to the fuel pump inlet.

 

[bentle]

Re: 94/95 Force 120 - bogs down at full throttle

Yes you would see fuel leaking from carbs. Replace any fuel lines left and check the fuel pickup tube in the tank. Most have a pre screen at the end and can get clogged and making it very difficult for the pump to maintain proper fuel supply to the motor. Don't use primer bulbs from walmart. I purchased 3 and they were all defective.
Make sure that primer bulb stays firm after priming . While priming and after priming there shouldn't be any full coming out of the tiny pressure relief holes on top left
Sides of carbs. If so then you need to pull fuel bowls and adjust your floats. There really is no way to see how full they are because of how they are mounted up to carbs.

 

[TwoFish]

Re: 94/95 Force 120 - bogs down at full throttle

I have just finished helping someone with a similar problem. They had a new clear style inline fuel filter. It didn?t allow enough fuel flow. He switched to a standard white Mercury inline filter and it fixed the problem.