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Yamaha V4 115 extreme miss above 2,000 rpm's, fixed by touching trim button

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bluespeedball

New member
Guys I apologize in advance for the stupid questions that I will be asking on the forum but I appreciate and and all help I can get. I purchased my first boat a month ago, a 1992 Alumaweld H56 with a Yamaha V4 115 Model C115TLRP. I purchased it from a widow whose husband bought it new in 2000. He passed away and it went to her son who also passed away. It has sat in a garage for the past 5 years and probably used less than 10 times. And for those of you that are thinking it No the boat isnt cursed......i think.

I brought it home and immediately drained the old gas out of the gas tank and filled with new 93 octane with the correct 50.1 ratio of Yamaha brand oil. I had a friend help me change the lower gear oil, installed new plugs and I paid someone to change the water pump as a preventive measure. I have to buy all 3 new batteries ( 1 start and 2 deep cycle for the 24v trolling motor. The boat it hardwired from the factory with circuit breakers instead of fuses. It has power tilt and trim and it does appear that someone has replaced the key switch at some point. That the history of the boat.

I have a healthy knowledge of automobile engines but very limited on my experience with boat motors. Heres my issue; the boat will not run above 2,000 rpm's with a severe stalling/ missing/ hesitation whatever your want to call it. It feels like at 2000 I have 1-2 coils that shut down. On my first test run I was just at idle making sure the boat didnt leak, that bilge pump and live well pump worked and things like that. I attempted to engage the throttle about 3/4 and it began to miss like I had lost a coil or two. I dont know what a two stroke suppose to sound like at idle, but this one sounds decent. While it was sputtering I began to play with the tilt and trim button and when I hit it, MAN it lit up and ran like it was being chased by the devil! Due to the sputtering I went back to idle and put it on the trailer.

I have read everywhere that these carbs will get junked up from sitting so I purchased two cans of spray seafoam and two can of mix. I mixed one can in a gallon of gas w/ oil and ran it at above idle through the engine. I poured the other can in the gas tank. I took apart the carbs and sprayed/ cleaned them but they were spotless on the inside. I decarb the boat with the other can as I have found instructed online. At this time I had a new trolling motor installed so i wasn't as afraid to get out in the water with it. I also tested all 4 coils to make sure ohms were within specs (yes I bought a v4 115hp manual). The coils were all within spec.

Today I took it out for the second time after the carb cleaning, decarb and coil test. Put it in the water and used choke, it started almost immediately. I put it in idle and eased out into the main channel. At this time I let the boat warm up for about 5 minutes. After this I started to engage the throttle a little more. Again at exactly 2,000 rpms the boat starts to sputter/ miss/ hesitate whatever you want to call it. I did fish this evening and on the way back decided to fully engage the throttle to see what would happen. I did and it started the missing immediately after 2,000 and wouldn't climb any higher. I remembered the trim/ tilt button and pressed it and she TOOK OFF! Im not talking about pressing and holding the button, but steady pressing the button every 1/2 second either up or down this boat is trying to come out of the water. After you release it she sputters and falls down below 2,000 rpms.

This boat is almost all stock, except for the key switch, trolling motor, batteries and fish finder. Im racking my brain here. If the coils were going out or bad, if the carb was dirty or gunked up the why is it running so well when I pressing the trim button. AND......why is the intermediate pressing off the button making the boat run like it should. This appears to me like a short in the wiring BUT what about the trim button and a short would IMPROVE performance? Shoudnt it decrease the performance? What should I look for in regards to the short, should I follow the trim power wires, inside the control box or something about the motor in the back? Should I ever be concerned about the coils or carb at this point.

I feel helpless that I have no further knowledge on this subject, I can do the work if Im just pointed in a direction to go in. I have spoken to two local boat mechanics that state the boat is probably just old. I have a lot of trust issues with shadetree mechanics, and the larger companies want to sell you another boat. I know this was a long post but if anyone could provide so help it would be so greatly appreciated.

i will respond quickly if anyone has any further questions or if I need to try something before we go any further.

Thanks
Robert
 
Try this. Get the motor started and warmed up, then disconnect the main harness connection at the motor. Take it for a short ride just long enough to see if you get over 2000. Keep in mind you won't be able to turn off, restart, trim or have a temp alarm until your harness is reconnected. This will isolate the fault to the motor or the boat. Then you will have some better info to proceed with. You could do all this tied off at the dock if the locals are ok with that and you are confident about your cleats and lines.
 
That is a great idea! Again Im not a boat mechanic by any means but that make a lot of sense.

Thanks
Robert

Also, I had the spark plugs replaced with new and the lower unit oil changed when I first got the boat. This being "preventive maintenance" I guess. I have been reading a lot on the buzzer alarm from within the handle control box. I verified that mine was disconnected and re-connected it. I have read that if its overheating or incorrect oil mix ratio it will go into limp mode and will not rev above 2,000 rpms. In fact there is a guy that posted a few up from me that is having the same problem but his buzzer is going off.

Could I have a coolant flow issue even though I just had a new water pump installed, or maybe even a thermostat (s) bad. I know that about every 5 years you can expect to replace a thermostat in a car, well.....whats the life expectancy in a boat. This boat almost 20 yrs old and appears the motor has not been touched. Are thermostats a "maintenance" item to be changed every few years?

Thanks
Robert
 
The 2000 rpm thing is suspicious of the warning circuit but since you don't have a horn going off you either have a bad horn and an actual overheat situation, a possible shorted pink wire somewhere or a shorted heat sensor. Ground one of your heat sensor wires out of the harness at the head with the key on and see if you get a horn. Temp is the only warning you get with this motor.
T-stats are a definite maintenance item but if this motor is used in salt water be careful you don't break screws. 6e5-12411-30-00 and 688-12414 gskt x 2.
 
The buzzer, or horn, was disconnected. I located this a few days ago and re-connected it but have not had it out in the water since. I had to install 3 new batteries and used sandpaper inside the battery terminals for a better connection but will double check.

Whether its called "limp mode" or "RPM reduction mode" does anyone know what the triggers are and what exactly happens to make it limit the rpm's to 2,000?
 
Guys thanks for all the help so far. This is what I got at the present time.
Took the boat out to the water after changing the poppet valve, t-stats and hooking up the alarm where it was previously unhooked. Left it on the trailer but backed into the water and again it would start but not rev over 2000 rpms. The alarm sounds as soon as you turn the key on and will not stop. Its not hot, its not even started and the alarm buzzer is sounding. BUTTTTTTT.......with the key on, the alarm going off, when I hit the tilt trim button up the alarm stops for as long as I hold the up trim button.

Now dealing with the alarm, I have disconnected both temp sensors and the alarm continues, I mix my own oil so thats not an issue. The alarm will stop by unplugging either wire (yellow or pink) that goes to it, disconnecting main harness from motor (therefore killing the power) or dis connecting the red fused wire going to the starter relay. Problem is all of these things kill the power going to the alarm but nothing I do seems to effect the closed grounded circuit causing it to go off.

Now as far as the trim button, I can disconnect all 3 wires going to the trim button, turn the key on and the alarm still goes off.

WHAT IS GROUNDING OUT?!!!
 
What is grounding out is the pink wire at some point. Look over the engine wire harness for any kind of chafe to ground. Did you try running it with the 10 pin connector disconnected? This will obviously kill power to the horn but if it the motor still is in rpm reduction mode then you at least know the problem lies only with the motor wiring. Sounding like the main wire harness has an issue.
 
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