Hard Starting

[Eastexn1]

I have a 2006, 50HP, 2 stroke Yamaha that is hard to start. I have cleaned and rebuilt the carbs and primer. Still hard to start. I have traced the problem, I think, to the fuel enrichment device. It is not activating when I engage the starter, and it is not warming up.. I have checked the power to the device and it is only getting 3.13 volts. The circuit in the manual seems to show 12 volts.

Is the 3 volts correct or should it be 12 volts.

Thanks
Bill

[99yam40]

the voltage comes from the lighting coil that charges the battery while motor is running.
but that closes the enrichment not open it
12v like the manual says

[robert graham]

Do you have the red Primestart lever in the correct "normal" position?....not "off" and not "on"......it's an automatic system...

[Eastexn1]

Hard starting

Yes, the manual choke is in normal.

[robert graham]

Try starting it in the "on" position.....if it starts easily then your Primestart system is not working as it should in the "normal" position and may require cleaning or service....

[seahorse5]

You are aware that the throttle lever has to be in the idle position for the enrichment system to work when starting, right?

If the throttle is advanced, the engine will be very hard, if not impossible, to start up cold.

[rodbolt17]

dang
seahorse lives
what seahorse says about the throttles.

[boscoe99]

When are you checking the leads to the Primestart device for voltage? Nominally 12 volts plus will be seen once the motor has started. Motor not running, no voltage to PS. Motor running, voltage to the PS.

Primestart is not a choke. It is not a primer. It is an automatic fuel enrichment mechanism. Adds more gasoline when it and the motor are cold, less additional gasoline as the motor warms up, and finally no additional gasoline when the motor is fully warmed up. It has three positions. Automatic enrichment, on (continuous enrichment) and off (no enrichment).

Make sure the red knob is turned fully counter clockwise. If that does not work then as Robert says, move it to the on position. What happens? If it starts well when cold then something is amiss within the carburetor. Make sure to turn the device either off or back to automatic after the motor starts and has warmed up. Otherwise the motor will run much too rich and waste gasoline.

Have you set the idle mixture screws correctly upon reassembling the carburetor? Maybe try turning them out half a turn or so and see if it starts better when cold.

If you are using gasoline contaminated with ethanol try and find rec90 or a brand that sells gasoline without any ethanol. Ethanol causes a lean fuel/air mixture. Lean is just what is not needed when the motor is cold.

[Eastexn1]

Bosch, thanks for the reply. 65 years of running engines has me calling this a choke, but I know this is a primer and have studied the operations of it. I replaced the device when the old one didn't work. Now, I feel the new one doesn't seem to work either. So, I checked to see if it was getting power, hence the finding 3 volts. Note, this was while the starter was spinning the engine, not while the engine was running.

The engine will start while in the auto enrichment ON position, but not in normal.
Carbs and prime start unit have been cleaned and rebuilt and adjusted. Fresh gas in place. New plugs installed. New fuel lines installed. It should run, but will not cold start without manual prime. I feel like the problem is in the prime start device, but can't isolate it.

Bill

[99yam40]

My C40 enrichment system should be very close if not identical to your 50.
I never found a very precise description of the workings of it, but I installed a clear tube where the extra fuel is sent to the intake from the enrichment device.
I could see liquide fuel pumped thru that line when red lever was turned to the on position while cranking the motor.
But I saw no liquid when in the auto position while cranking.

best I can tell when in auto the motor sucks a little extra fuel thru the needle and seat of enrichment system along with some air from the bowl vent on #2 carb but it is enriched fumes that go to the intake not liquid fuel.

on my C40 I pump primer bulb until firm , leave the warm up lever down throttle in neutral, and turn key for a few seconds. wait a few seconds and do it again. if no start I try again.

usually will fire off by the 2nd or 3rd try

if it has sat for a long period of time (weeks) it may take 4 or 5 trys.
the fuel/oil mix left in carbs will evaporate some and leave a very oil rich mix in the bowels that is harder to fire off at first .

where are you located ?
I have read others in real cold climates had problems with cold starts not enough fuel getting thru.

Maybe you just have not got everything cleaned up enough

[Eastexn1]

Thanks yam40. I tried all of your suggestions and tried to start the engine. Tried to start it by turning it over for approx. 4-5 seconds each time. No luck. Flipped the manual start red lever to ON and it started immediately. Left it run for about a minute to warm up. Killed it and tried again with manual in NORMAL and it started every time.

But, it still won't start in NORMAL when cold, and I live in North Texas and the temp today is 60F.

This pretty well confirms my suspicion that the electronic primer device is not working.

Bill

[boscoe99]

Bosch, thanks for the reply. 65 years of running engines has me calling this a choke, but I know this is a primer and have studied the operations of it. I replaced the device when the old one didn't work. Now, I feel the new one doesn't seem to work either. So, I checked to see if it was getting power, hence the finding 3 volts. Note, this was while the starter was spinning the engine, not while the engine was running. Starting voltage does not mean anything. Running voltage (12 plus volts) is applied to the device to take it out of the enrichment mode once the motor and the PS device have both been warmed up.

The engine will start while in the auto enrichment ON position, but not in normal. This is the way that it should be. Automatic is the normal setting. If the motor starts cold when in the automatic mode what is the problem? If and when it will start in the ON position then it has to be taken out of the ON position once the motor has warmed up. ON is not the normal position for the valve to be in.
Carbs and prime start unit have been cleaned and rebuilt and adjusted. Fresh gas in place. New plugs installed. New fuel lines installed. It should run, but will not cold start without manual prime. What is meant by manual prime? To me that would be the ON position but you say your motor does not work with the valve in the ON positioin. I feel like the problem is in the prime start device, but can't isolate it.

Bill

See comments above.

[boscoe99]

My C40 enrichment system should be very close if not identical to your 50.
I never found a very precise description of the workings of it, but I installed a clear tube where the extra fuel is sent to the intake from the enrichment device.

PRIME START CARBURETOR
Most of the current 40 to 90hp engines are equipped with Prime Start carburetors. A conventional choke is not required on these carburetors. Fuel enrichment for starting a cold engine is provided by the Prime Start System. To control fuel enrichment for starting and warm-up, an electrothermal valve/enriching fuel pump assembly is mounted on the carburetor. The enriching fuel pump is actuated by pulses from the crankcase. The electrothermal valve is heated by power from the lighting coil. The enriching pump draws fuel from the carburetor float bowl and pumps it to the electrothermal valve unit which controls the amount of enrichment fuel. This fuel is then drawn into the intake manifold with the assistance of intake vacuum to enrichen the fuel mixture entering the combustion chamber. The electrothermal valve is normally open, with the amount of valve opening determined by ambient temperature. After the engine starts, power from the engine’s lighting coil begins to heat the electrothermal valve. The valve expands as it is heated, so its valve seat starts to close, con*****ing the amount of enrichment fuel passing through it. The electrothermal valve heater is energized as long as the engine is running. Therefore, the valve opening is continuously reduced, which restricts enrichment fuel flow once the engine has warmed to normal operating temperatures. The valve assembly also has a three-position manual override valve. This valve can be set for automatic or manual enrichment or set to turn off the enrichment.

Automatic Enrichment
With the manual override valve set in the automatic position, enrichment of the engine will take place depending on the temperature of the engine and the electrothermal valve. Enrichment will take place automatically as outlined previously and as long as the throttle valves remain closed during cranking.

Manual Enrichment
When the manual enrichment lever is at the open position, the fuel is drawn by the enriching fuel pump and led directly to the intake manifold through the passage selection valve. Air will not be drawn for primary mixture in this setting. When starting the engine with the manual enrichment lever open, the lever should be turned to the closed position immediately after the engine has started.

Manual Enrichment Closed
If the power source for the electrothermal valve should fail with the valve fully open or the electrothermal valve fail to close, the manual enrichment lever should be turned to the closed position. After starting, the engine can be run normally with the valve in the closed position.

[99yam40]

Boscoe99 I did see things like this, and I guess they are fairly well informative,
but when I was 1st playing with mine back then I was not getting liquid fuel out of the enrichment system going to the intake in normal position and asked several places if I should be.

No one could answer that. I finally gave up because everyone said that if it starts good enough to not over think it.

I was suprized to see liquid fuel come out when it was in the on position but not in the automatic(normal) position

[99yam40]

That is a lot better than my hand drawn pics I did back then.
And it looks like it shows a liquid fuel flow to intake when in the on position and a mixture of air and fuel in the auto (Normal) position