im am out of ideas and need help.

from the top.
about two weeks ago i was out fishing. about dark we cranked up to head to the landing. about a minute into the trip the outboard started skipping a little and got worse quick. within 100yds i dropped of plane and it stalled it cranked but would immediately die. so i put my backup plugs in and it fired right up and ran good. back on plane no problem but within 400yds it died again. it would fire up and die within 3 seconds but i could keep it going with a little throttle in neutral. so i thought i might have trash in my carbs. i was able to drain 2 of the 3 carb bowls and it fired and we were able to putt back to landing a little faster than idle speed.

i have never put anything but no ethanol gas in my boat. before this trip i did purchase No E gas from a different station. that paired with it seeming to work after draing the bowls made believe i had a fuel issue. i purchased and installed a 10 micron fuel/water separator and siphoned my tank out and put fresh no E fuel from my usual store and treated it with marine stabil. i cleaned the carbs and installed all new line from the tank(10 gal plastic) to the outboard. i took it to the lake and it seemed to run good but minutes into my test run it started skipping and got worse. i circled back to the landing and came to a stop. it died but fired up and started to get on plane again but was running rough put died before getting there. it would crank with no hesitation and die within 3 seconds.

back home i figured a little trash had somehow got in the carbs again so i cleaned them again. went back to the lake and had a repeat of the previous trip. i did make 1 mistake. i took apart the fuel pump on the block to clean any trash out of it and i believed i damaged it as it later leaked in a test. i got a new one and installed it. another test run seem to be its self ran good for a mile or to then the old skip started again and this trip ended like the last one. cranking and dying within 3 seconds.

last things i have done is borrow a hanging gas bottle from a mechanic friend and hooked it up inline right before the new fuel pump eliminating the whole fuel system.with the foot in a barrel. let in idle as the engine warmed it started running rough.this test ended with it again cranking easy but dying within seconds. even with increased throttle in neutral. 

the spark seems strong but quits when the engine starts dying. i had a friend mention the power pack and they can break down and act strange with heat. is there anyway to test or trouble shoot that.

and lastly i have not messed with this electronic thing on the side of the middle carb. can someone explain what it is and can it cause trouble. in my reading and research i have not figured out what it is or even seen it mentionedweb pic mine are in better condition

Maybe the engine starts dying when the ignition quits.  It seems you have pretty much ruled out it being a fuel problem.

That looks to be some sort of primer system. Give me your engine model code and ill take a look online and let you know for sure. If its that, what that does is give you the ability to rope start it when the starter fails. In the wrong orientation of that red lever it should give you issues starting though.

 

I immediately thought fuel pump, being that you replaced it im guessing that is not it.

 

When you say cleaned the carbs, did you fully take them apart including the passage plugs, soak them and rebuild them? If not with that engine being 13 years old id buy the carb kits to do all of them. Id then tear them down being sure to remove all core plugs and soak the entire bank in a 70% pinesol 30% water mixture for 24 hours. When thats done id rinse them with water, blow it dry with compressed air(you can use a can if you dont have a compressor) and then blow them out again with carb cleaner. After that rebuild them. This cant hurt your chance of narrowing this down. Make sure you get the floats set correctly, take pics at EVERY step.

 

The other thing is this could be a bad coil also. If the powerpack fails you likely will not have power on any cyl. Older mercs are known to eat powerpacks, lucky for you I dont think this one is under the flywheel. I could be wrong but I doubt it. I had to edit this as I realized this is not a merc but a yammy.

 

Get a spark tester for each cyl, and put one on every cyl then fire it. See if they all fire. If they dont all fire take a coil from one that fires, move it to the one that doesnt fire, hook it all back up and see if the loss of spark follows the coil. If it does you know you have a bad coil, if it doesnt  you likely need a power pack.

WOW that powerpack is $550

 

Id try this

 

http://forums.iboats.com/Yamaha-Outboards/Stroke

 

Heck the carb kit for one carb is $50

 

Once you know your model number you can look up the diagrams here

 

http://www.boats.net/parts/search/Yamaha/Outboard/2000/parts.html

 

EDIT: looks like you asked on the other forum already unless your twin is having exact same issues.

To me it sounds like a powerpack problem as well- is yours a 2 or 3 cylinder engine?  I would think that you the way it loses power you may also have an override to shut the engine down if you don't run on more than the minimum.  Easiest way to diagnose is to hook your engine up to a laptop, see if your cylinders are firing properly, or figure out which one may not be- take off power pack from a working cylinder and switch it with the one that does not work.  If the original cylinder now works fine, than you know what powerpack to replace.

 

You may also have an alarm that drops it to 1 or 2 cylinders or shuts it off altogether.  You have a local dealer you can plug into?

tried a few thing i have read and was recommended. it took much longer for the symptoms to show up today. it did eventually start stalling at idle, but i could keep it running with throttle which seems to me to eliminate electrical. i cleaned the carbs one more time and believe i found trash in 1 of the carbs. so i have my fingers crossed and will try again tomorrow. how there was still something in there with all the flushing replacing and cleaning is mind boggling.

 

when i say cleaned the carbs i take them all the way down removing everything and spraying out all jets and passage. these carbs look new they are completely spotless. 

tried a few thing i have read and was recommended. it took much longer for the symptoms to show up today. it did eventually start stalling at idle, but i could keep it running with throttle which seems to me to eliminate electrical. i cleaned the carbs one more time and believe i found trash in 1 of the carbs. so i have my fingers crossed and will try again tomorrow. how there was still something in there with all the flushing replacing and cleaning is mind boggling.

 

when i say cleaned the carbs i take them all the way down removing everything and spraying out all jets and passage. these carbs look new they are completely spotless. 

 

That does not necessarily eliminate electrical.  In fact, it could point to electrical.  The throttle also affects ignition timing  If your motor's ignition timing involves any mechanical movement of the ignition system, that movement may be causing a short in the electrical system.  I know older motors used to have a "plate" between the flywheel and the engine block that rotated slightly around the crankshaft to advance or retard the timing.  A "pigtail" wire could be shorting out when the timing is in certain positions.  We had a car that would do that, only when driving down a level road at a constant speed.  Didn't matter what that speed was, as long as you weren't accelerating or slowing down.  Hold the throttle steady and the engine would die.  As the car slowed and the timing changed it would come back to life.  The insulation on a pigtail in the distributor had worn off, and when the plate in the distributor was in one particular position, the wire would contact the distributor housing, shorting out the ignition.

 

I don't know if or when the timing became a computer function rather than mechanical on outboard motors.

 

If the timing is controlled electronically, then I'm guessing there is a sensor, or maybe more than one, that sets the timing based on throttle position, and other factors such as temperature, air flow, etc.  A faulty electronic component may be causing the problem you are experiencing.

That problem sound familiar.   You might want to check your gas line hose from the tank to the motor.  There could be a small

leak letting air enter the line, thus starving your engine of fuel.

i have eliminated the fuel system. i had a friend who is a mechanic come over and look at it. we went through the electrical system. once it got warm it started its run and cut off routine we unplugged a thermal censor and it would run much better not perfect but better. part #12 on this diagram.

http://www.boats.net/parts/search/Yamaha/Outboard/2000/C40TLRY/ELECTRICAL%201/parts.html

 

using the ohm feature on a voltmeter you can tell when it gets hot it completes a circuit. 

 

does anyone know what temp this circuit is supposed to operate at?

I have had a similar issue with mine and i since read up that these Yamaha outboards go into limp mode when there is a temperature issue or a 2 stroke oil pump malfunction, it limits the motor to 2000rpm enough to get you back to shore. I know this doesn't solve your issue but i just noticed it wasn't mentioned in the forum thread.

Faulty censor cutting off the motor?

 

May be time to bite the bullet and take her into a qualified mechanic to run a computer check to find the problem.