115HP cutting out at 2500 RPM

[dbradley]

I have a 2000 C115TLRY that was running rich. I rebuilt the carbs with OEM Yamaha parts, new plugs, fresh fuel mixed 50/1.

All 4 floats are adjusted level with float bowls and all 4 idle adjustment screws are backed out 1 1/2 turns.

Motor starts and idles fine, once I get up to 25+ MPH and somewhere between 2000-3000 RPM, I hear a solid tone alarm coming from instrument cluster and motor starts to shutter. Once I back the throttle off the alarm stops and motor stops shuttering, I can duplicate the issue everytime I get in that RPM/speed range.

Any help is greatly appreciated

Thx Dave

[rodbolt17]

try testing the overtemp switchs.
as the C motor is not oil injected about the only other alarm is overtemp.
its either overtemping or the switchs are failing.

[dbradley]

Thx rodbolt! I wasn't sure what the alarm was indicating but now I do, is there an easy way to check the overtemp switchs?

[rodbolt17]

pull them and heat them in water with a candy thermometer and see when they open and close with an ohm meter.
most likely you have scale built up under the head.

many conversations about various scale remedies.

[dbradley]

Over heat issue resolved. It was NOT the over temp switches as suspected.

Its like they say when all else fails, get and read the service manual!

Going back to my original post, I had said that my floats were adjusted level with float bowls and idle adjustment screws (now I know they are called pilot screws) were adjusted 1 1/2 turns out. The reason for that adjustment is because 1- thats where they were adjusted before rebuild and 2- all over this forum folks are saying that these motors like to run at 1 1/4 to 1 1/2 turns out. Well upon reading the service manual it says that the 115 HP motor pilot screws should be adjusted 5/8 turn out. In the trouble shooting section, incorrectly adjusted pilot screws was the first cause of overheat. I readjusted per manual and presto no more over heating!!!!!

That little motor was humming today with zero issues and pushed my Carolina Skiff Sea Chaser 186 at almost 5100 RPM and right at 50MPH on the GPS!!!!!

Get the service manual and read it! Listen to these good folks advice on the forum. They know what they are talking about. Thanks again Rodbolt.

[rodbolt17]

don't know what you did but that pilot adjustment screw had NOTHING to do with any overheats.

if you carefully study the pilot fuel circuits two things JUMP out.
that carb has both pilot AIR and pilot FUEL jets.

means on that carb the A/F ratio is FIXED.

the pilot adjustment simply lets more or less of this FIXED ratio past.

so to make the actual air to fuel ratio so lean that the extra heat would overwhelm the cooling system above 2500 RPM is a stretch of the imagination.

by backing that adjustment screw out almost double your making the engine run rich not lean.
richer running means its cooler.

difference between welding with gas and cutting with gas is additional oxygen.


was this service manual a factory Yamaha or an aftermarket manual?

[dbradley]

Rodbolt-The service manual was an internet down load and has Yamaha all over it and covers all models of the 115 HP along with some additional HP's. Soooooo it appears legit, its not the one you would buy at Pep boys that starts with a letter "C", I forget name.

I tried to copy page from service manual and include in post for you to read, but not sure how to do it. I could very well be telling you incorrect names for pilot screws, idle adjustment screw etc, but I did what the manual pointed to and said to do, it SEEMS to have worked. Maybe just coincidence.

If that was in fact an overheat alarm, I could repeat it regularly in same RPM range. If I backed throttle off, alarm would go off and engine would run right, as long as I stayed in lower RPM range. As soon as I got back up on plane, alarm would sound. It seems if it was over heating, it would stay overheated at any RPM once it was too hot. Just thinking of when a car overheats, you cant make it stop over heating by just letting off the gas.

Was planning on going back to lake this morning but it is a down pour in Atlanta, so will have to go Thursday. Hopefully same results

[rodbolt17]

I will try this one more time.
your trying to convince me that by altering the PILOT adjustments,mostly used at idle but still used at WOT, you can increase the combustion temps so much that the overtemp SWITCH, on or off, can close?(on)
that means the cyl head just exceeded about 180*F.

one thing that car doesn't do is circulate RAW water from a raw water source through the engine block.

on a RAW water cooled engine,even in fresh water, minerals tend to build up scale. scale is worse in blind passages and such.

leads to temporary false overheats that quickly correct themselves once the load is taken off the motor.

I have seen some freshwater only motors with brick hard scale that could only be removed with a small hammer and a modified screwdriver.

but typically what your describing is a scale build up under the cyl head passage where the thermoswitch is located.

this assumes that the rest of the cooling system has been properly maintained.

that raw water scale from mineral deposits is why for many many years both outboards and raw water cooled inboard/sterndrive t-stats were less than 145*F.
much above that and it accelerates scale and salt/mineral deposits.

its why we have more issues with moden raw water cooled EFI inboards and sterndrives.
they are designed as auto engines and tried to be adapted.
so now they have to run 160-165* t-stats due to engine and fuel system and EPA requirements.
most EFI 4 stroke outboards have 160 T stats as well now.

but I would be surprised if closing off the amount of pilot A/F mix by 3/4 of a turn would affect engine operating temps.
if anything it should make it slightly higher.

[dbradley]

Im not trying to convince you of anything Rodbolt. You are the master mechanic and I am the novice here, which is why I am on the site (trying to learn like most of us here). I am not trying to piss you off either but please remember that most members do not know it all and you are generally dealing with folks who have 1/10th the knowledge you moderators do. All I am saying is that what I did SEEMS to have worked and all I can do is hope for the same results in the future. It was not the over temp switches as you thought and there could be scale build up to the ninth degree just as you say BUT for now its not over heating. Thx again for your help

[rodbolt17]

I don't know it all and don't claim to.
however I have better than 30 yrs repairing broken gear and the last 20 + on outboards and stern drives.

I cant remember if the C model also has a low battery alarm. most the V4 and V6 did but that's because it had to have 12V for oil transfer.

my guess is you still have issues that haven't been resolved.

my old 130 did that and it was quick enough that the time it took to drop off plane,pop the hood to test the switch to see which side was overtemping the alarm quit.

that's your first clue its scale.
if you actually manage to overheat it it takes 15-20 minutes to cool back down and open the switch.

the other side is if you do have carb issues and you masked them,even if you did make it leaner(hotter) the only reason the hot horn would sound then is the piston is dragging on the cyl wall creating excessive heat.

you do as you wish but your not going to solve any problems on that motor with a 3/4 turn(or less) adjustment in or out with the pilot air screw.

[dbradley]

Rodbolt- You actually hit on something! I did in fact change the start battery from the last outing to this outing, that is the ONLY other variable that has changed.
I was going to ask if there was such thing as a low battery warning but thought it was way out there. I took the battery (only one, no dual system)out after the last outing and put it on a charger and then kept it on a trickle charge, the strange thing is the damn charger gave me no fault errors of any kind. Once I got back to lake, motor trimmed up and down fine to remove transom saver but when I backed into water the battery seemed to be dead. I changed it out with a spare and it ran fine.

So are you saying it could possibly be a "battery alarm" instead of an "overheat alarm"??? I don't see anything in book on battery alarm but I would feel a whole lot better if that is what it is!

If it was a low battery alarm, and my pilot screws are 5/8 out, should I leave them there or adjust them richer? Its running fine at just over 5000 RPM and pushing near 50 MPH.