50hp Choke won't open

[jackmanjls]

1997 50hp
On this engine I've rebuilt the carbs, checked the gas line for obstructions and replace several hoses.

It seems to start fine and runs at idle but the choke never opens. What controls the choke opening?

How can I test the prime start device, that's on #2 card w/red switch lever?

[boscoe99]

A 50HP Yam two stroke does not have a choke. It has an automatic fuel enrichment device that Yamaha calls PrimeStart.

Did you clean the prime start fuel pump and ensure that it is in good working order?

Did you test the prime start device itself to verify that the needle extends when 12 volt power is applied to the electrical leads?

Did you verify that the red lever is in the automatic (counter clockwise) position?

[robert graham]

If it cold starts fine then the fully automatic prime start device is working properly and the red lever is in the proper position....why screw with it?...

[boscoe99]

I read the OP as the motor is providing too much fuel once it is warmed up. That is, it is not automatically reducing the amount of fuel and is providing too much.

Years ago when cars had manual chokes it was common to see someone riding down the road belching black smoke. They would forget to push the choke knob in. Gas was so cheap then it did not matter how much fuel was being blown out the exhaust.

[robert graham]

Maybe he's got a bad fuel pump diaphragm causing rich mixture....I don't think these prime start units give much trouble......

[99yam40]

1997 50hp

How can I test the prime start device, that's on #2 card w/red switch lever?

I am sure the service manual has the steps needed if Boscoe's info was not enough for you.
If you are working on this motor you should have the correct Yamaha service manual