1999 90HP Force surging at WOT

[rreichstadter]

I recently purchased a 1999 Force 90HP outboard. Motor has great compression, 155 on all 3 give or take a psi. Installed the motor on my 16ft Boston Whaler and ran great the first couple of times no issues. My buddy took it out the other day with his family and it started right up and he got to the resume safe speed zone and tried to open it up and it died then no start. He got towed back and when I popped the cowling immediately noticed the top spark wire plug had come completely off of the spark plug. Problem solved.

Popped it back on and it started right up. Next time I took the boat out, started fine and ran great until about 3/4 throttle, it starts to drag a little bit. When it is WOT it runs ok but surges forward then back down again. It continues to do this at WOT, surges to normal WOT speed, then back down to what would normally be about 3/4 throttle. If I have it at 3/4 throttle it runs normally.

Seems like a fuel issue, I have cleaned the carbs, replaced all the gaskets and fuel lines and same problem. I have not messed with the fuel pump yet. The top spark plug wire that had come off when my buddy took it out jiggles a little more than the others, could it be losing connection intermittently at high speeds or do I need to dig deeper into the fuel issue? there are a couple of smaller fuel? lines that seem to be going into the power head itself? Gonna change these too as they seem a bit flimsy. Not entirely sure what those are for...Thanks in advance. Happy to post pics or videos if that helps.

 

[pnwboat]

Might be the fuel pump. Have someone squeeze the primer bulb 4 or 5 times as you go to WOT. If that solves the problem, then change the fuel pump diaphragm. Replacing the fuel pump diaphragm should be done on a regular basis especially with the ethanol fuel these days. The same goes for the water pump impeller. Also might want to check the primer bulb itself. It has a "one-way" valve that sometimes goes bad and actually restrict the flow of fuel.

The smaller fuel lines are most likely part of the fuel recirculation system. This only comes into play at low or idle speeds. The fuel tends to pool up in the intake passages and cause a rich mixture resulting in poor low speed/idle performance. The recirculation system bleeds off the pooled up fuel and dumps it into the cylinders before it becomes a problem so it can be burned to minimize the impact to low speed performance.

 

[rreichstadter]

Will do. I will update as soon as I am able to get back out on the water, probably tomorrow night. Thanks!

 

[rreichstadter]

Sorry took me a while to get back out. So, I rebuilt the fuel pump with an OEM kit. Put it all back together. Cranks and idles fine, when I go to give it throttle in gear it just dies. It's possible I messed something up when I rebuilt the fuel pump but I'm pretty confident I put it all back together the way it was. When I squeeze the bulb gas flows through and fills up the in-line filter after the pump. Any thoughts? I'm gonna take it back apart and make sure it's all where it's supposed to be.

 

[Nordin]

When you open it up try to squeeze the primer bulb.
It sounds like a fuel issue. Pull the carbs and clean them again. There might be some debris in the high speed circuit in some of the carb/carbs.

The setting of the air/fuel mixture screw should be 1-1,5 turn out from lightly seated.
As your engine is a late Force I assume it has a priming system for cold start and not a regular choke butterfly.
Try to prime it when you open it up. If it then hang on, you have a carb issue maybe an air leak somewhere.

 

[pnwboat]

You can do a quick test to see whether or not the check valves in the fuel pump are installed correctly by removing the outlet hose on the fuel pump that goes to the carbs. Disconnect the hose right at the carburetor inlet fitting and try blowing into the hose. If you can blow through it, then you have a check valve that is not working. You should not be able to blow into the outlet hose that goes towards the fuel pump. The check valves insure that the fuel only flows towards the carburetors.

Make sure you don't have some type of blockage in the fuel supply line to the fuel pump. Maybe possibly a problem with the fuel pick up in the tank.

Also make sure the the gas tank vent is open. If you have any doubts about the gas tank vent, just loosen the gas cap enough to allow air to enter the tank and see what happens at WOT.

 

[rreichstadter]

Sounds good, do I need to unhook the hose at the other end ( line to fuel pump from tank) as well or just leave that hooked up?

 

[jerryjerry05]

Could be: Bad inline fuel line connector, bad hose, bad squeezie, tank vent line clogged, fuel pump bad, exhaust in the cowl,
​pickup tube in the tank clogged, filter clogged.
The squeezie has a one way valve it can go bad.
Does the squeezie get hard hen pumping it up?
The inline connector has rubber in it and it can go bad and suck air.
Check for water in the system.

 

[rreichstadter]

Interesting development. I took it to the ramp to try and troubleshoot today and after reading a post about a similar issue I tried slamming it into full throttle from neutral and it flew up on plane and ran great! I backed it down and it ran fine until I got to just above idle speed and it cut off. Cranked it up and tried to creep up to speed and it bogged out like it has been. Slammed it into full throttle and it flew again. Took the cowling off and noticed that one of the recirculating hoses was hanging off and occasionally the motor will cough at idle and a puff of exhaust shoots out. I'm going to replace all the recirculating hoses, thinking maybe it's affecting compression or possibly causing exhaust under the cowling to choke the motor off? Any thoughts? Thanks to everyone who has responded thus far.

 

[pnwboat]

Depending on which end of the hose was disconnected, it may be affecting the air/fuel mixture to one of the cylinders making it leaner than it should.

The vacuum effect is greater in the crankcase at low speeds because the throttle plates are not wide open, so more outside air may be sucked into the cylinder through the hose at low speed as opposed to WOT. Regardless, hopefully you've found the problem.

 

[jerryjerry05]

Another thing that could happen: the choke or enricher could be bad??
​It also has rubber in it, a diaphragm.
The rubber can go bad and cause excess fuel in the system.
The hose/ hoses try pinching it off after it's started.

 

[rreichstadter]

Awesome. One thing I have noticed is I feel like sometimes I hear a little click when I "choke" the enricher to start and sometimes I don't. It had occurred to me that this piece might be going bad but I had it in my head that it would only affect starting and not once the motor was running. Luckily I have a complete parts motor! I'm going to switch it out as well as change out all the recirculating hoses for good measure. The parts motor is a couple years older than the one I am running so not 100% match but hopefully it will show me where that little dangling hose is supposed to hook up. Thanks again all, will update asap. Good thing I have an auxiliary boat with an immaculate 25 horse merc, the trout have been on fire here in NE FL!

 

[rreichstadter]

Finally got a chance to mess with the motor. I went to Oreily's and got the yellow "lawnmower" gas line that was a perfect match for my recirculation lines and replaced them. Pain in the butt to get to all the connectors but it's done. Had to take the starter off to get to one. Anyway. Cranks, runs, idles great, same stalling problem at low speed. If I push the fuel enricher on the ignition it runs just fine and when I go to accelerate it will accelerate normally while pressing the key in. To be precise, if I press the key in it revs up a little and then will run fine for 5 or 6 seconds at slow speeds then start to die if I don't push it again. Once it's WOT it runs and sounds perfect. When I back it down it wants gas again. Thinking I just need to rip the carbs off and go through em again. Any thoughts?

 

[jerryjerry05]

That sounds like a fuel pump problem.
Sucking air at low speeds??
Get a 6gal tank.
Run a hose direct from the tank to the fuel pump.
​Take it for a spin.

 

[rreichstadter]

I have a 6 gallon tank hooked straight to the fuel pump, I bypassed the merc fuel fitting in case that was the culprit. I did just rebuild the fuel pump but it's possible I didn't put it back together correctly? Like maybe got the gaskets swapped or something. I'm going to re-build it to spec as soon as I get a chance and re-post.

 

[rreichstadter]

Checked the fuel pump by blowing through like pnwboat suggested and sure enough I was able to blow through it the both ways. Took it apart and realized I put one of the "skeleton" gaskets on the wrong side of the "flat" full gasket. Anyone know the proper terms for these? When I put it back together I could only blow somewhat in the direction of flow and not at all in the reverse. Put it all back together and looking forward to Wednesday when I take her out. Thanks everyone, I will update asap.

 

[Nordin]

The "skeleton" gasket you refer to is a check valve.
There is one at the inlet that allow the fuel to flow in and not back/reverse and there is one at the outlet.

 

[rreichstadter]

Thought the check valve was the little clear plastic circles. I'm talking about the gasket that is cut out to kind of trace the line where the metal comes together. I don't think I'm doing a very good job describing it!

Third from the right if the link works...

 

[rreichstadter]

Not quite the link I was looking for...

 

[pnwboat]

If you can blow through both ways, I would think that the check valve(s) are not installed properly. Maybe not, but I would take a close look at them.