'99 90hp Please, Please Help

[gatortrout]

I just bought a '99 90 hp yamaha 2 stroke.It runs perfect until my 2nd or 3rd stop while fishing then it cranks perfect and idles but sounds like it is only running on 2 cylinders or is flooded on 1 cylinder. Sometimes I can unkook the gas and run it dry and hook it back and prime it and it will work great but more often than not no.I checked and it has spark on all three cylinders and I changed the plugs.What is strange is that in reverse I seem to have power but in foward it bogs down at about 1400 rpm's.I was wondering about the check valves? Please help I have a tournament this coming weekend.wcarver@peganet.com

[IFish4Tuna]

Check your fuel pump(s) for a leak or faulty diaphram. If you don't have the manual to check how to do this. There's pretty good info on the web for how to do it. $40 ish to replace them. Best to check before replacing. Pretty easy to do. Especially w/ practice [img]smile.gif[/img]

Also have you tried a different gasoline source.

If it aint spark, it's fuel.

Also, not sure if it runs better at high rpm under load, or if just and idle issue. If ok under load, could be stuck open thermostat that's throwing the EFI off amd putting to much fuel in. Since you just bought it, they may have never been replaced or serviced well.

Good luck - Ed

Ed

[gatortrout]

I thought it was fuel related but I do not smell gas or see any leaking.It idles great always even when it it won't run over 2000 RPM's.It sound like it is going into RPM rediction but I replaced the water pump and thermostate and it is running cool and no buzzer goes off.It's like something is telling it that it is overheating and it's not.I also tested the temp sensor and it is good.I can not make it do it at home.It only does it after running after about an hour of total use and then when I crank it it is RPM reduction.

[Ken]

gator',
You need to first test the alarm system.
Unhook the two wires that go to the thermo switch (about 4 inches from the switch) and short them together (the ones that go back to the CDI) with the ignition on, motor not running. You should immediately get an alarm. If not, then faulty alarm buzzer or associated wiring.
Assuming your motor is not going into rpm reduction (alarm sounds and motor shakes violently and rpm is automatically reduced), try checking the primer bulb when the motor boggs down. If it has collapsed, then there is a fuel restriction from there on back to the tank. If the bulb has not collapsed, then try pumping the bulb several times till hard. If motor rpms pick up, then you have a faulty fuel pump.
You could also have a sticky carb float valve. I would do a shock treatment with SeaFoam or RingFree - that not only de-carbonizes the motor but also cleans the fuel system.
If none of the above helps, then I would suspect a thermal problem with the CDI.
Good luck [img]smile.gif[/img] ,
Ken K

[gatortrout]

Thanks for all the help.I found out my fuel pump is good as well as my buzzer and primer bulb so I am again back to square one again until I go fishing this weekend.I can not duplicate the problem at home it runs great.My engine does sound like it is going into rpm reduication but is is running cool and no buzzer and it not oil injected.Is it possible the CDI or stator is heating up and giving a false overheat singal to the motor?If it would break and stay broke it would be easy to find but when it only happens after a few hours of running then runs great at home it is hard.Any more ideas are welcome greatly.Thanks

[1d10t]

you could be shorting out from one plug wire to the block. That would cause it to miss badly. Also, if the neutral safety switch is not working properly it will tell the motor that it's not in gear and that could be the cause of your power in reverse but not forward... Then again it could easily be non of the above... Ken will know what to check next.

[Ken]

gator',
Thermal related problems like this are tough to fix since they don't occur all the time.
Did you try pumping the bulb when the symptom appeared?
The neutral switch that Bob mentioned, I believe, will only keep you from cranking the motor when it detects a "non-neutral" condition.
There is only one thermo-switch on your motor, and it is the only thing, as far as I know, on that pre-mix that will put it into rpm reduction.
The only thing left, assuming everything else is working, is the CDI, the stator coils, and the high voltage coils for the spark plugs.
I would put in new spark plugs, if you haven't already.
The most likely suspect is, of course, the most expensive, the CDI.
When the motor boggs down and you come back to idle, does it idle smoothly? If not, try removing the hood and disconneting spark plug wires one at at time (use an insulated tool, of course) to see which cylinder is the dead one. If you can determine this, then try swapping coils to see if the symptom follows the swap - if so, then you have a coil breaking down on you after it heats up.
If the above does not help, then it's probably gonna be the CDI breaking down after it has warmed up. Maybe try a can of electronic equipment "cool-down" (freon) from Radio Shack and try to cool the CDI when the symptom appears to see if that makes a difference.
Good luck, and let us know what you find out [img]smile.gif[/img] ,
Ken K

[jb123]

try running motor at night , look for any arcing around plugs and coils.
try to isolate the cylinder after running ,motor is warm, by pulling the plug wires while running, listening for the change.
i remember old vehicle coils when going bad, after heating up would act up also, tho ive never seen this on an outboard.

[gatortrout]

Thanks for all of the help as soon as I find something out I will let you know Thanks again.

[fishcall]

yamaha 90 hp

Thanks for all of the help as soon as I find something out I will let you know Thanks again.

Did you ever find out what was wrong with your 99 Yamaha 90hp when it wouldn't go over 2000rpm. My 2010 model with only about 60 hours is doing that night.

[robert graham]

I have the same exact motor as yours and I'll be real interested to know what you find out about this. My best guess would be some issue with the fuel delivery, from the fuel tank pick-up,fuel tank vent, tank connections, primer bulb check valves, fuel line quick disconnect on cowl, fuel filter/o-ring, fuel pump, sticking float bowl needle valves. Have you drained each carb onto a clean white cloth to check for water or debris? With float bowl drain plugs out, pump the primer bulb to flush out float chamber and float needle valves. Check bottom cylinder sparp plug after running for wet/fuel fouling condition indicating bad fuel pump diaphragm and very rich condition on that cylinder causing bad running. Fuel pump very easy to change with 2 screws. Good Luck!

[robert graham]

Same exact motor as mine. I would check the fuel system from the tank pick-up tube,tank fittings, both primer bulb check valves, fuel quick-disconnect on motor cowl, fuel filter/O-ring, fuel pump, carb float needle valves, drain all 3 carbs onto clean white rag to check for water or debris, with drain plugs out pump primer bulb to flush float chamber and float needle valves, check bottom cylinder for wet/gas fouling condition caused by bad fuel pump diaphragm causing very rich condition on that cylinder/plug. I just replaced my fuel pump just to be safe since it had the original(1999)pump on it, kept the old one for a spare. Pump replacement very easy with 2 screws. Let us know what you find and Good Luck!

[dorf]

Anti-siphon valve in the fuel tank outlet fitting could be sticking !!! It can be removed by punching it out.(spring and ball affair)

[ozzyd]

You might need a New CDI module.