Motor goes from WOT to troll speed then back to WOT without moving throttle.

[platypus]

--Suzi 90 hp ... seems like it might be electronic fuel injection issue?
--At WOT engin drops to troll speed momentariy then back to WOT.. doesn't seem to sputter like bad gas, water or sucking air.
--My 9 hp runs on same gas tank and doesn't miss..large engin doesn't miss or sputter at troll speed.

--I'm thinking it is electronic? Any way to check myself or just have to bite the bullet and take it into a shop.

 

[SmokeOnTheWater]

Check and/or replace the fuel filter. With all the discussion of water in the ethanol fuel we buy it may be a clogged filter, water does not go through your filter element. Sounds to me like your engine is starving for enough fuel. Good luck and hopefully I saved you a few bucks?

 

[platypus]

--should have mentioned I changed gas filter and no difference.
--the more things I eliminate the more I'm thinking it is electronic which I can't fix myself... was hoping someone might have had the same problem with a magic bullet solution like its just a loose ground wire.
--the way it is working I would still have my 9.9 to make it back and I'm not fishing that far from home with winter weather... closest dealer is a three hr drive but that looks to be what I'm going to have to do.

--thanks.. never hurts to change gas filter as you suggested it is a common problem.

 

[Bduck]

A fuel pump can act like a clogged filter sometimes. I've run across this issue on an outboard & an installed generator on a motorhome. These were older machines but still have the basics of air, fuel, & ignition. To me it sounds like its a fuel issue.

 

[Paul S.]

Quite a bit of the electronics in the more modern engines can be temperature sensitive. Does this happen after it's been running for a while and warmed up? And does it do this on a regular cycle; such as x minutes run time then idle down for a few seconds, another x minutes run time and again idle down? Will it do it when the engine cover is taken off or does that make any difference?

To start with, I'd be checking all the wiring plugs to make sure they're clean and tight. Also any wires that are grounded. .screws can work loose. The more you can eliminate before biting the bullet and hauling it in, the less (maybe) the shop will have to check.

 

[platypus]

--after running for awhile... never sputters at troll speed.... seems like a regular cycle run at speed then idle down for a few seconds then off again at speed... haven't tried it with cover off... seems to be good stream of water coming from pee hole at troll and high speed.

 

[Paul S.]

The way your describing it, it sounds like it's one of the electrical components/modules getting ready to fail. I'm not familiar enough with outboard engines to be able to say just which one, but if that were a car engine I'd say it was something to do with the fuel injection system. You might call the local dealer and describe the problem, he might have run into that before and could tell you what needed to be replaced without actually having to see the engine or hook it to their 'puter.

Just a thought. . .sorry I couldn't have been more help.

 

[platypus]

--was thinking the same thing computer problem... was hoping there was a reset or reboot somewhere. I took all connections apart and then back together plus ground... haven't tried it in the water yet but I didn't see anything that looked loose and no sign of any burnt wires or loose gas lines.
--as it doesnt backfire or sputter I'm thinking it is fuel injectors shutting down... it never actually stalls just goes to troll speed then back up to full.
--will probably wait for spring check up and just stay close to home until then... still have 9.9 kicker to get back to the dock.
--dealer is at least 3 hr drive
--thanks

 

[Paul S.]

I got to thinking about it and remembered I had a similar problem with my older (2001) Arctic Cat snowmobile. On flat ground, everything was fine but come to a steep hill and WOT and it lost RPM's. Back off on the throttle for a few seconds and it would take off again like a scalded cat, only to fall on it's face after a minute or so. This was not a computerized machine and had a carb and not injectors. Come to find out, the fuel pump was going out. After adding a cheapie electric fuel pump, the problem vanished.

Just another thought. . .

 

[lowe1648mt]

Also look for a vacum leak between the motor and tank. If it has removable fuel connectors, the "O" ring some times fails. Primer bulbs get old and squishy. They sometimes collapse.

 

[agitator]

You might want to look at the exhaust port plug depending on what year it is . Google suzki exhaust port problem nasty deal but ya gotta fix it .

 

[kelmark2590]

It sounds to me like it may be an idle air control valve (IAC Valve)

The IAC valve opens and closes to keep the engine at a constant idle by regulating the amount of air going into the engine. You can check it out by putting a credit card over it and then sliding it back and forth to allow more or less air in.

 

[platypus]

It sounds to me like it may be an idle air control valve (IAC Valve)

The IAC valve opens and closes to keep the engine at a constant idle by regulating the amount of air going into the engine. You can check it out by putting a credit card over it and then sliding it back and forth to allow more or less air in.

--That sounds like it may be the issue as I thought it might have been a pluged air vent to the gas tank.
--The engine does not miss or sputter just drops to idle then back up to full speed as if rapidly pulling throttle back and then hit to WOT

--so many things... I did check for water in gas, changed filter... but the engine does not miss nor does my 9.9 that runs with no problems from the same tank.

 

[kokphiser]

My reply might be to late but i'll say it anyway! I had a outboard that would do this and to find out I was sucking air on my fuel line. From the tank to the fuel pump there is no pressure so it wouldn't leak, but it sure will suck air and starve engine momentarily of fuel ! Maybe this will help if not too late!

 

[platypus]

--thanks as all of the suggestions or combination may be the cause I just have to work through each until I find the problem and can correct it.