1988 88hp Johnson dies after WOT

[nastyquedawg]

My 88hp Johnson dies to idle rpm after running at WOT for about 45 secs. Need some suugestions on what to check.

 

[DJ]

Re: 1988 88hp Johnson dies after WOT

Fuel restriction. Outbaord or inboard fuel tank?

 

[emdsapmgr]

Re: 1988 88hp Johnson dies after WOT

Next time you run the engine in the lake, have someone constantly prime the fuel hose primer bulb. This will force extra fuel into the carbs. If the engine runs fine at full throttle, you probably have a weak fuel pump. (the pump won't pump enough fuel to keep the carb bowls full of fuel at wide open throttle.) Those pumps are not real expensive and are easy to change.

 

[nastyquedawg]

Re: 1988 88hp Johnson dies after WOT

So I was unable to run the boat with someone pressing the primer bulb. I went ahead and installed a new fuel pump. In the event that this does no solve my problem, what else could iI check. The gas vent line seems to be clear.

 

[emdsapmgr]

Re: 1988 88hp Johnson dies after WOT

Let us know how the test with the new pump went-we can make suggestions then...

 

[nastyquedawg]

Re: 1988 88hp Johnson dies after WOT

So I took the boat out on Saturday. Hammered the throttle down and the boat ran at WOT for about 45 secs before dieing back down to idle. So I bring the boat home. Take off the carbs and used a compressor and blew in every hole there was. Put the boat in the water on Monday. Hammered it down and the boat ran for about 1 minute before dieing to idle. I tried it two or three times and it did the same thing. Brought the boat back home, took off the carbs, and used a thin wire and stuck it in every hole I could see on the carbs. Please let me know what else I can check that might be causing this problem. Can it be a power pack or a coil?

 

[emdsapmgr]

Re: 1988 88hp Johnson dies after WOT

Sounds like a fuel supply issue. The engine is consuming more fuel than the pump can provide at max rpms, draining the carb bowls-and returning the engine to idle. If this is the case, the engine should reaccelerate after the pump fills up the carb bowls again-starting the cycle over again. You could have an issue with the fuel hose, the bulb in the fuel hose, or the tank could be a problem. If running from a built in tank, make sure the anti-siphon valve ball valve is moving normally-if there is grit in the check ball valve, it may restrict it's movement and fuel supply. Make sure you have no air leaks in the fuel hose system under the cowling.

 

[nastyquedawg]

Re: 1988 88hp Johnson dies after WOT

So i replaced the anti siphon valve, the fuel hose coming from the tank, and installed an Evinrude primer bulb. The hose coming from the tank to the nipple on the boat was 7/16 fuel line. I thought that was a bit big for the boat. It appeared wet coming from the tank and the clamp was not tight. I replaced the line with 3/8 fuel line. When I took the old anti siphon valve out there was no ball. I took the fuel pickup out of the tank and did not see it there.I hoping that the previous owner removed it because I never found it. There was some type of wire mesh in the pick up tube and a small piece of plastic debri, i cant imagine that causing my motor problems though. I am assuming the wire mesh is suppose to be there as some type of filter. Changed all the lines under the cowl also. I hope to be able to make another sea trial this week, any more suggestions if this does not work.

I do appreciate you helping me. Thanks

 

[emdsapmgr]

Re: 1988 88hp Johnson dies after WOT

That engine will run fine on 5/16" fuel line, so the larger 3/8 line will be O.K. Any fuel leak means there is an air leak also. Air leaking into the fuel system will cause lean conditions-good that you found it. The prior owner may have had problems with the ball in the anti-siphon valve and removed it. They can collect dirt and cause fuel restrictions. You don't need to have one-many folks remove them for that reason. Sounds like the wire mesh in the fuel tank pickup is doing it's job.

 

[nastyquedawg]

Re: 1988 88hp Johnson dies after WOT

Boat ran fine. The air leak at the nipple on the fuel tank was the problem. I did readjust the idle. It only took a new fuel pump, 3 different carb cleaning sessions, a new antisiphon vavle, new fuel lines under the cowl, new fuel line from the tank to the fuel water seperator, and a new primer bulb. Its about 750rpm when in forward gear. I would like a little more rpm when in neutral, would it hurt anything if I bumped it up another 100 rpm while in forward gear.

 

[emdsapmgr]

Re: 1988 88hp Johnson dies after WOT

The recommended 650-750 rpm usually affords a nice idle (won't load up and die.) More specifically, that rpm range affords smooth shifting. Higher idle is not a problem-but does stress the clutch dog and gear faces a little more when shifting into gear. (make sure you vigorously thrust it into gear with a quick snap of the wrist each time.) It would be unfortunate to run with a higher idle, when that adjustment is actually covering up for another problem-like dirt/dried fuel in a carb idle passage which can affect smooth, low rpm idling.