86' 90hp Power loss at full throttle after 5mins

[imported_Rosey]

HI Guys,

I'm having a problem with my engine where it starts, ideals very well. When I open it up it responds as expected and remains responsive for approximately 5mins. Then all of a sudden I loose around half the power. I can hold the throttle fully open and the boat barely gets up on the plain. I still have response in the lower rev range but can not get full power to return. This has happened the last two times the boat has been on the water. Each time it runs great for around 5mins of full throttle then goes bad.

The engine is running a newish simple fuel pump (ie.VRO removed) and appears to be feeding fuel though the clear filter under the cowling without any issues.

Can anyone shed any light on what could be happening?


Thanks

 

[Joe Reeves]

Re: 86' 90hp Power loss at full throttle after 5mins

If the fuel primer bulb looks like it may be collapsing somewhat, that would indicate that a fuel restriction exists. In this case, fuel would be applied normally to the engine properly for a short time, BUT as that restriction lingers the fuel pump can no longer overcome the restriction and the engine runs lean of fuel.

Check the fuel bulb itself as one of the valves may have seperated and would be drawn back into its casing backwards which would act as a shut off valve, then check the following:

(Fuel Anti Siphon Valve)
(J. Reeves)

Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vaccum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.

NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models.

The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.

The above procedure will cure a restriction problem with the anti siphon valve as stated. BUT, it may also allow fuel to drain backwards to the fuel tank when the engine is not running (siphoning backwards) due to the fact that the carburetors/fuel pump etc are higher than the fuel tank. This condition is not an absolute as the valves in the fuel primer bulb usually prevent this backwards siphoning problem. However.... if this does take place, the cure would be to install a new anti siphon valve.

http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store

 

[emdsapmgr]

Re: 86' 90hp Power loss at full throttle after 5mins

I agree with Joe, look for a fuel restriction first. Try squeezing the primer bulb when it is not running well, see if it will run normally with constant squeezing. This will overcome any problems with the fuel pump. It is not uncommon for electrical problems to surface when the engine comes up to operating temperature. You could have an electrical component failing, causing loss of one or more cylinders. Try taking a timing light out on your next trip. When it misfires, connect your timing light to each plug wire. See if you get sharp, strong, constant flashes fro the light. Check your plugs by pulling them and see they all look the same: if any are wet, vs dry.

 

[imported_Rosey]

Re: 86' 90hp Power loss at full throttle after 5mins

ok will try above, thanks guys