1998 C90 new powerhead tuning

[boscoe99]

Thank you I thought I was going blind or just crazy.

The one with pink wire at the top I think is over heat
the one with orange wire is the warmed up switch

Apparently your C90 is not the same, as I cannot find another switch on your motor, so I have no idea how it is suppose to know when the motor has warmed up

For your blindness there are actions you can take to stop it.

For craziness there is no cure. Comes with being a Yamaha owner.

[boscoe99]

Thank you I thought I was going blind or just crazy.

The one with pink wire at the top I think is over heat yes
the one with orange wire is the warmed up switch yes

Apparently your C90 is not the same, as I cannot find another switch on your motor, so I have no idea how it is suppose to know when the motor has warmed up

I don't think it does.

[flounder daddy]

The seloc manual shows that it does control the warm up timing. Says to disconnect the pink wire and fire up the engine and it should bypass the sensor. I just did that on the muffs and sure enough it fired up and idled back down to 900rpm or so and had its normal snap. Its showing that it works on resistance and has a temperature chart showing temps with coresponding resistance values all the way up to 212*F which would be a very hot engine. Manual states that the colder the sensor, it will add timing untill it reaches a specefied resistance and goes to normal idle down mode. I think it has certain settings/resistance for certain tasks. One for cold start, one for normal, and one for buzzer alarm. It goes into the black box with circuits inside, so who knows what is inside the box.

[boscoe99]

The seloc manual shows that it does control the warm up timing. Says to disconnect the pink wire and fire up the engine and it should bypass the sensor. I just did that on the muffs and sure enough it fired up and idled back down to 900rpm or so and had its normal snap. Its showing that it works on resistance and has a temperature chart showing temps with coresponding resistance values all the way up to 212*F which would be a very hot engine. Manual states that the colder the sensor, it will add timing untill it reaches a specefied resistance and goes to normal idle down mode. I think it has certain settings/resistance for certain tasks. One for cold start, one for normal, and one for buzzer alarm. It goes into the black box with circuits inside, so who knows what is inside the box.

The Seloc manual does not appear to agree with the Yamaha manual.

The Yamaha manual calls for the thermoswitch to close at or about 183 ~ 194 degrees F. Only one thermoswitch is called out for the 1998 C90, whereas the C40 uses two, which are different from each other with respect to opening and closing temperatures. And they have different functions.

Are you sure you have a C90TLRW?

Is this the thermoswitch that you are talking about?



Is this fun or what?

[flounder daddy]

Yes, that is the switch. It just used 212* (the boiling point of water) as a ohm test at a high range. That has to be tied to the CDI unit because it will limit RPM and the only thing limiting RPM on the engine is the CDI. Gonna let the engine get cold overnight and try again in the morning. It states that the thermo-sensor provides data to the CDI unit for YMIS operation. Thermo-sensors are not the same as thermo-switches. One has a resistance range, one is on/off only. The sensor has the range, the switch is the on/off.

Now that I have re-read the manual, its showing its main use is for overheat/buzzer. So im kinda wondering now what the heck is sensing heat for the idle warm up.

[flounder daddy]

This is really got my head hurting trying to figure it out. What would advance the 10* of timing when on high idle/cold start and sense temp?? I just ran a jumper wire from the pink wire on the harness side to the ground wire and it did buzz the alarm. Im almost wondering if something in the CDI box is not liking cold. Im really lost at this point. Im gonna go ahead and replace the temp switch, but now im kinda doubtfull that its the cause.

[flounder daddy]

Doing more investigating. The 1998 C40 uses 2 of basically the same style of "pot" shape resistance switches. One they care calling a thermo sensor, the other a thermo-switch...
This is a ebay auction with the seller selling both temp sensors/switches off a 1998 40hp, they look identical to the C90 switch. So maybe it is right.

Yamaha Outboard 40 HP Elrw 1998 Thermo Switches 689 82560 00 00 6H4 | eBay


This is the stuff that keeps me from sleeping at night I swear.

[boscoe99]

Doing more investigating. The 1998 C40 uses 2 of basically the same style of "pot" shape resistance switches. One they care calling a thermo sensor, the other a thermo-switch...
This is a ebay auction with the seller selling both temp sensors/switches off a 1998 40hp, they look identical to the C90 switch. So maybe it is right.

Yamaha Outboard 40 HP Elrw 1998 Thermo Switches 689 82560 00 00 6H4 | eBay


This is the stuff that keeps me from sleeping at night I swear.

You need to throw away the Seloc book. Does it cover a Yamaha C90 and a C90 only? I doubt it. Those books are mostly generic and try and cover too many Yamaha models which can be similar or completely different. I think you are getting misleading information.

The C40 uses two thermoswitches. Switches, as in they are opened or they are closed. That's it. Zero resistance when it is closed and infinite resistance when it is open. One thermoswitch to indicate an over temperature condition and one thermoswitch to tell the cdi if the motor is cold or warm.

Never heard of a resistance switch.

There are thermosensors used in some Yamaha models but neither the C40 or the C90 use one.

The C90 uses one thermoswitch. One only. It only tells the cdi if the motor is too hot.

The core problem is that you don't have the applicable Yamaha service manual. A sub-problem is that the Yamaha manuals do not give theory of operation.

[flounder daddy]

The resistance switch is just a term I am using. Im not a yamaha factory tech, doing the best I can with what I have here. Im a tool and die machinist with a V8 race engine machining/automotive performance background prior to machining. This is the page out of the manual I have.

[boscoe99]

Thank you I thought I was going blind or just crazy.

The one with pink wire at the top I think is over heat
the one with orange wire is the warmed up switch

Apparently your C90 is not the same, as I cannot find another switch on your motor, so I have no idea how it is suppose to know when the motor has warmed up

Can you imagine sitting at a desk at Yamaha trying to answer 50/60/70/80 questions a day about all of the models that Yamaha US has offered between 1984 and today? And all of the various types of gauges. And all of the various types of control boxes and other rigging stuff? What wire is used to do what and does it provide 12 volts or does it apply a ground? What is the thread size and pitch of a connecting rod bolt? What propeller is to correct one for my motor? What gauge wire is used on the main engine harness for?
What do the diodes do in my motor? How does a sensor work? What is a choke plate? What is a Primestart? Why do some models use choke plates and other don't? Why does my propeller rattle? Where do I get locktite xyz? What is the torque for my propeller nut? How do I get engine data on my chart plotter without using the Yamaha gateway because it is too expensive? Why are your prices so high? What happens on my motor when sensor xyz fails? At what resistance on my thermosensor will my temperature gauge indicate 212 degrees? My GPS says I am going 41.7 mph but the Yamaha gauge says I am going 41 mph what is wrong with the gauge? Why do you have to call me back? Why can't you answer my every question here and now?

Talk about going crazy.

[boscoe99]

The resistance switch is just a term I am using. Im not a yamaha factory tech, doing the best I can with what I have here. Im a tool and die machinist with a V8 race engine machining/automotive performance background prior to machining. This is the page out of the manual I have.

Wrong manual.

I admire your effort and persistence.

[flounder daddy]

Can you imagine sitting at a desk at Yamaha trying to answer 50/60/70/80 questions a day about all of the models that Yamaha US has offered between 1984 and today? And all of the various types of gauges. And all of the various types of control boxes and other rigging stuff? What wire is used to do what and does it provide 12 volts or does it apply a ground? What is the thread size and pitch of a connecting rod bolt? What propeller is to correct one for my motor? What gauge wire is used on the main engine harness for?
What do the diodes do in my motor? How does a sensor work? What is a choke plate? What is a Primestart? Why do some models use choke plates and other don't? Why does my propeller rattle? Where do I get locktite xyz? What is the torque for my propeller nut? How do I get engine data on my chart plotter without using the Yamaha gateway because it is too expensive? Why are your prices so high? What happens on my motor when sensor xyz fails? At what resistance on my thermosensor will my temperature gauge indicate 212 degrees? My GPS says I am going 41.7 mph but the Yamaha gauge says I am going 41 mph what is wrong with the gauge? Why do you have to call me back? Why can't you answer my every question here and now?

Talk about going crazy.

What does any of that have to do with this thread? No reason to post stuff like that. Im trying to solve a problem and thought I could get some help on this forum. Its a very odd problem, I get that. Im not expecting answers imediately either.

[flounder daddy]

Is there a number for yamaha USA that I could call and ask a certefied tech what controls the start up temp sensing?

[rodbolt17]

hay lucy.
I spalined it once.
the C90 does NOT use any method of warm up detect.
the CDI at start up simply uses a time constant circuit to advance ign timing for a set period at each start cycle.

some 3 cyl Yamaha models do use a separate thermosensor to give feed back to the ECU. the c90 is not one of them.

yes there is an 800 # for Yamaha.

you are chatting with at least one Yamaha certified master technician.

biggest issue, your a raceum car bubba.

forget anything you thought you knew about them thar raceium cars.

it does not apply to high performance 2 strokes.

fix your fuel system.
go fish.

go to any ford,chebby, or Honda dealer.
tell the lead tech your vehicle runs well but after 15 minutes at 5000 RPM it falls out.
watch that techs peepers glaze over,
they never see any auto engine run much longer than 13 seconds at that RPM.
us boat moto mokanicks see 5500-6000 RPM runs that last hours.
longest I ever ran my F150 at 5700 RPM was about 45 minutes.
longest I ever ran my 455 olds above 5000 was about 13 seconds.

[99yam40]

After Rodbolts input I myself would monitor the timing at start up to see if the idle timing does or does not advance at start up and then drop back to normal after a set time.

See if the timing drop back follows the high idle you are seeing.
I had to replace my CDI on my C40 because the idle timing was retarding too far. They do go bad sometimes, but not very often.

But as he said you may have a fuel problem not a timing problem. check to see, timing is easy enough to monitor