Can`t find choke system on 50 hp 2stroke 1989 motor

[99yam40]

Bosco99 I have sent you a PM

[boscoe99]

Bosco99 I have sent you a PM

Email sent.

[99yam40]

My thoughts are that it is a totally different set up than the 50. I do not think there is a processor con*****ing the solenoid

[boscoe99]

My thoughts are that it is a totally different set up than the 50. I do not think there is a processor con*****ing the solenoid

I don't have a complete understanding of how it works.

From the SM I can see that the CDI is getting information from the extra thermoswitch as to engine temperature (cold versus warm). The CDI is also wired to the enrichment valve. I don't see why the processor in the CDI cannot simply be opening the enrichment valve when the motor is cold (thermositch open) and then closing it when the motor is warm (thermoswitch closes). That would be my best guess as to how it is functioning. But I was wrong once before.

Looks like the progression of the model was first a mechanical choke. Then an enrichment valve (on or off fuel enrichment). Then came Primestart which is a variable fuel enrichment mechanism. And then came EFI.

Alas, there is no theory of operation from Yamaha that I can find anywhere that lays it all out. The only mention I have ever seen of it was with respect to the V76 model.

[99yam40]

Your guess is about the best I can think of too.
That V76 info you sent is a complicated system,
Do not think Yamaha would do that on a 50, but who knows

[boscoe99]

Maybe Rodnut, when he wakes up some time this afternoon, can offer some advice. If he can get his head to think clearly that is.

With the exception of one valve per carburetor versus one valve for three carburetors I don't see the cold start fuel enrichment system of the V76 being that much more complicated. Now certainly if you throw in the fact that the valves open to combat detonation, and for other reasons, yes, it is more complicated.

I once thought of two strokes as being simple. The V76, and it successors the OX66 and HPDI two strokes can be about as complicated as an EFI four stroke. I will say it time and time again, pity the poor Yamaha mechanic who has to deal with all of these types of motors with almost nothing to go on. Customers can't understand why a repair might take so long. For all I know it took so long because might take hours and hours to understand the system and then take but minutes to do the repair. Think what happens when a rodnut retires. He takes all of that knowledge with him. Hopefully, he is able to pass on some of it to the younger guys.

[99yam40]

Maybe Rodnut, when he wakes up some time this afternoon, can offer some advice. If he can get his head to think clearly that is.

With the exception of one valve per carburetor versus one valve for three carburetors I don't see the cold start fuel enrichment system of the V76 being that much more complicated. Now certainly if you throw in the fact that the valves open to combat detonation, and for other reasons, yes, it is more complicated.

I once thought of two strokes as being simple. The V76, and it successors the OX66 and HPDI two strokes can be about as complicated as an EFI four stroke. I will say it time and time again, pity the poor Yamaha mechanic who has to deal with all of these types of motors with almost nothing to go on. Customers can't understand why a repair might take so long. For all I know it took so long because might take hours and hours to understand the system and then take but minutes to do the repair. Think what happens when a rodnut retires. He takes all of that knowledge with him. Hopefully, he is able to pass on some of it to the younger guys.

That was what I was meaning, it operates for more than just the cold enrichment

[rodbolt17]

hay
I resemble that remark.
actually I was good last night, only had 1 can of beer at midnight.
so the head is good today .

I cant remember much about the system on the 50. the V76 I can chat with you about.

best I recall on the 50 it used a thermoSWITCH for overheat detect and a thermoSENSOR for ign timing when cold and cold enrichment,all con*****ed by the ECU/CDI.
if I make it by the shop this weekend I will try to look it up.
ya gotta remember in that time frame I worked on gray boats not play boats.

on the V76 system the enrichment could be used at rapid acceleration,deceleration and when knock was detected as well as cold start.

[bogunnar]

Sorry for me missunderstanding you guys. What you call plate I call butterfly.
In post#4 the plates yellow marked I thought was throttle plates.
I will attach a pic, so you can see there is no choke plates neither a "electrical gizmo". All 3 carbs seems to be exact same on the outside. I have had motor since new. This winter I do the first repair on it - water in LU due to leaking seals near water pump ( shaft seals). I stil even is on my original impeller! A fantastic motor. Okay boating season is short in Scandinavia, but it has had a hard life in salt water and driving through a lot of sandbanks and too little service.

[IMG][/IMG]

Sorry I couldn't rotate pic to vertikal position (I use TinyPic)

[rodbolt17]

take a pic of the port side, those carbs definatly don't look to have choke plates.

[boscoe99]

Sorry for me missunderstanding you guys. What you call plate I call butterfly.
In post#4 the plates yellow marked I thought was throttle plates.
I will attach a pic, so you can see there is no choke plates neither a "electrical gizmo". All 3 carbs seems to be exact same on the outside. I have had motor since new. This winter I do the first repair on it - water in LU due to leaking seals near water pump ( shaft seals). I stil even is on my original impeller! A fantastic motor. Okay boating season is short in Scandinavia, but it has had a hard life in salt water and driving through a lot of sandbanks and too little service.

[IMG][/IMG]

Sorry I couldn't rotate pic to vertikal position (I use TinyPic)

Here is the photo in the right direction. As Rodnut notes, post a photo from the other side. The other side is where the fuel enrichment solenoid should be located.



I normally refer to the gizmos that control airflow through the carburetor as throttle valves. They are typically in the middle of the carburetor. Ahead of the throttle valves in some carburetors you will find what I can a choke plate. A butterfly valve by definition could be either the throttle valve or the choke plate.

but·ter·fly valve
noun
1.
a valve consisting of a disk rotating on an axis across the diameter of a pipe to regulate the flow, as in the throttles of many engines.

[bogunnar]

Realy quick reply! Its late and dark over here so I will shoot the pics tomorrow.
Butterfly or plate doesnt matter as long as we do not missunderstand each other. In automotive industry, I have learned the hard way, there are often different words for same thing in NA and UK.

[boscoe99]

Realy quick reply! Its late and dark over here so I will shoot the pics tomorrow.
Butterfly or plate doesnt matter as long as we do not missunderstand each other. In automotive industry, I have learned the hard way, there are often different words for same thing in NA and UK.

Certainly we yanks and the brits don't always speak the same language.

Now where is that zeno fellow from down under? Us folks from 'up above' need to be hearing from him as to the English language. The Aussie's speak their own version.

[bogunnar]

Yes it looks like a solenoid. Is this a PrimeStart device? and is it automatic?

Thanks again for your help guys!

[boscoe99]

Yes it looks like a solenoid. Is this a PrimeStart device? and is it automatic?

Thanks again for your help guys!

That looks to be it.

It is called a "solenoid valve assembly" by Yamaha in their parts book. It is automatic.

Primestart is similar but different. Both have a similar function, that being to provide a bit of extra gasoline when the motor is being started cold.