2001 Yamaha 50hp tlrz 2 stroke with prime start system starts and dies

tdave

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I have a hard to start problem with this motor. I try to start it with the red choke lever in "Normal" position and it starts for 10 seconds, sputters and dies. If I start it with the choke in the "Open" position it starts runs and idles perfectly. I have rebuilt the carbs, set the screws on the carbs out 1.5 turns open, checked timing marks, verified the prime start system is working properly. I put in new plugs, verified they are firing, new fuel filter etc. I do not know what else to check. I unplugged the blue wire from the prime start verified 12v with engine turning over and verified the that the thermo heater plunger expands and contracts as it should. Compression in all cylinders is 125. What else should I check and what harm is there if I run it in the choke open position? Thanks, Tom.
 

gm280

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Fuel pump and hoses from the tank... Look at those to verify you are getting fuel flow to the carb(s). Also check the tank vent and primer bulb you normally squeeze up before you start then engine. Just some ideas.
 

tdave

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Thanks for the quick response I have checked all of those items and all is fine. I am stumped why it starts, runs and idles so perfectly with choke in open position.
 

gm280

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Thanks for the quick response I have checked all of those items and all is fine. I am stumped why it starts, runs and idles so perfectly with choke in open position.
I guess I'm now confused. So the engine starts, idles and runs fine with the choke in the open position. Isn't that what it is supposed to do? If it then dies, maybe the carb float level it too high...IDK
 

tdave

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The engine is supposed to start and be run with the choke in the "normal" position. There are 3 choices via a red flip switch on the back of the middle carb 1. Normal, 2. Open, 3. Emergency. Tom
 

99yam40

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prime start system is not a choke.
but like you said in normal it should add extra fuel when motor is cold and then close off the extra fuel as the motor warms up.
if it will only run properly in the open position, that bypasses the thermal unit and dumps fuel as long as you have the red lever in open.
the pilot jets/passage in carbs could have a problem and not allowing enough fuel in .

once the motor warms up completely can you place the red lever into the off position and still have the motor run and idle well?
that shuts off all the extra fuel.
actually in the open position the motor should run to rich and not run properly after start up

I would also check what the timing is doing at start, idle, and upper RPM cold and warmed up to see if that is all in spec
 

tdave

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Not sure what you mean by Off position. The red selector lever can only be switched to normal, open or emergency. I have run the motor up to about 4000 rpm in the open position while on the water and switched the lever to normal and the rpms jumped to 4500. I was not running at full throttle. With the lever left in the normal position I idled down and the engine sputtered and died.
 

robert graham

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Maybe carb float needle is sticking in the closed position and not allowing motor to run more than 10 seconds....
 

99yam40

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Not sure what you mean by Off position. The red selector lever can only be switched to normal, open or emergency. I have run the motor up to about 4000 rpm in the open position while on the water and switched the lever to normal and the rpms jumped to 4500. I was not running at full throttle. With the lever left in the normal position I idled down and the engine sputtered and died.
that red switch has 3 positions normal, open, and off

sounds like the carbs need a good cleaning
 

boscoe99

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Not sure what you mean by Off position. The red selector lever can only be switched to normal, open or emergency. I have run the motor up to about 4000 rpm in the open position while on the water and switched the lever to normal and the rpms jumped to 4500. I was not running at full throttle. With the lever left in the normal position I idled down and the engine sputtered and died.
Normal is the automatic position.

 

tdave

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First, thanks for the response and let me say I think we may be talking past each other due to terminology. As I stated above, on my engine the choices for the red flip switch are Normal, Open and Emergency positions for this lever. According to your diagram 1 of these positions is "off". The motor is supposed to start and be run in the Normal position but does not. It starts and run perfect in the open position which is in the center of the 3 positions available. I am not grasping the Off position in the diagram as it relates to my 3 choices Normal, Open and Emergency. Tom
 

99yam40

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open is the emergency position since it provides fuel if it will not start in normal
off should be the 3rd position, it turns off the extra fuel incase the needle does not shut it off when in normal and warmed up.
if left in the open position the motor should run too rich.
sounds like the carbs need to be cleaned better
 

boscoe99

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First, thanks for the response and let me say I think we may be talking past each other due to terminology. As I stated above, on my engine the choices for the red flip switch are Normal, Open and Emergency positions for this lever. According to your diagram 1 of these positions is "off". The motor is supposed to start and be run in the Normal position but does not. It starts and run perfect in the open position which is in the center of the 3 positions available. I am not grasping the Off position in the diagram as it relates to my 3 choices Normal, Open and Emergency. Tom
Where in your manual are you seeing an "emergency" position? What page please? The manual for your model is LIT-18626-04-48.

The manual says to "open" emergency starter valve. That is, turn it to the "open" position.
 

tdave

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Where in your manual are you seeing an "emergency" position? What page please? The manual for your model is LIT-18626-04-48.

The manual says to "open" emergency starter valve. That is, turn it to the "open" position.
The emergency position is labeled right on the engine in front of red selector switch. The manual I have is Lit-18626-06-94, 63B-28199-1F.
 

boscoe99

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The emergency position is labeled right on the engine in front of red selector switch. The manual I have is Lit-18626-06-94, 63B-28199-1F.
Wrong manual for your model. In the scheme of things it should not really matter.

Neither manual shows the term "emergency" for the Primestart component. Yamaha is terrible about manuals not agreeing or parts and a manual not agreeing. Neither manual shows a label for the "automatic" position either.

Anyway, I trust that you now know the situation.
 

99yam40

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any way you look at it the motor should run in the automatic/normal position, your will not.
time to open up the carbs and find out what is plugged up
 

tdave

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Well after replacing the center carb and rebuilding the top and bottom carbs the engine fires right up in the normal position, runs for about 30 seconds and dies. No sputter at all it's as if you turn the key off. It will fire right back up again, run for about 30 seconds and die. Have checked fuel delivery from tank thru carbs and to spark plugs and all appears to be working fine. Can it be something electrical? Again this is a 2001 Yamaha 2 stroke 50HP TLRZ with very little run time on engine. Battery is good also.
 

99yam40

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does it continue to run if put in the open position like you 1st told us back in 2021?
also verify what the timing is doing with a timing light.
timing does change up as the motor starts, idles, and then warms up.
plus the light will show if the spark drops, but may be hard to tell if spark stops before or after it dies
 

tdave

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Runs the same no matter what position the prime start lever is in. Starts with first turn of key and idles up for some 8-10 seconds during warm up but then idles down to about 1500 RPM as it should. Has about 30 seconds run time after starting. Plan on doing some voltage/ohm checks tomorrow trying to narrow things down.
 
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