Pro 50 poor acceleration

[TownsendsFJR1300]

Can you post exactly what parts link your looking at for the rest of us?


Ok, so when you push the key in for choke, your closing ALL the choke butterflys, correct?
So your enrichening the A/F mix momentarily....

I gather you confirmed fuel in the #3 bowl by pulling the drain screw (when the carb SHOULD BE FULL). Carb can be spotless, by no / not enough fuel to it, it won't work...


As posted, a broke/failing reed should be spitting fuel back thru the carb and it's pretty rare they fail (IME)..


You should be able to remove the reeds fairly easily to inspect them for wear, etc...

Might want to do a Leak Down test at TDC. Even thou a 2 stroke, any excessive leakage at TDC could indicate bad rings, bad head gasket, etc.

[zenoahphobic]

Looking at the spark plugs picture, there appears to be adequate oil and that no. 3 did run quite a long time by the evidence of carbon build up around the outside rim.
What's evident is the clean porcelain suggesting lack of fuel not a continuing lean running problem.
When you clean the carby you must force compressed air throughout to check that ALL the passages are clear. Even if you think it is clean, you cannot see all of it.
It therefore also helps to carefully use a soft wire in these channels and jets. It will be something permanently adhered that is stubborn to move.
You can use a syringe with fuel on a dry carby to test whether all the passages pass fuel.
A key thing, you said it had fuel in the bowl, but I would check that the needle and seat do actually open.
Fiddly and careful work is required.

[Freaky1974]

This motor is a pro 50 2 stroke - 1992
it doesn’t have a choke , it had an enrichener - check out the picture

carb Is clean - soaked, blew air through passages and verified fuel in bowl

I can spray fuel in cylinder with no effect - it’s not the carb

I ran the motor yesterday, that’s why the plugs look like they do
it’s not fuel related
compression is right @ 100psi

i can cover the bottom carb when the motor is running, the motor will smoke and run rough

it’s not spitting fuel thru the carbs, but I can’t feel it pulling air like the others - upper reed on the stbd side has a different feel than the others

[99yam40]

So looks like this is a P50TLRQ,
I fail to see why that would be hard to post when you started this thread so everyone knows what motor you are talking about.
or when we asked several times for a model #

I am not familiar with one of these Solenoids, I have seen chokes and prime start systems, but I am not sure what this does since it looks like the same as the prime start,but the device is called a solenoid.
does it open a passage when you push the key in to allow extra fuel to be injected into the intake?

If spraying fuel into the carbs does not help,then extra fuel does not help the cylinders fire properly.
so how does pushing the key in help?

[TownsendsFJR1300]

The "parts" picture is too small to be usefull...

Is this your engine: https://www.boats.net/catalog/yamaha...lrq/carburetor ?


(It would certainly be easier if you could JUST SIMPLY POST WHAT LINK your using).


If so, it has "Prime start", pushing the key does NOTHING, that's all automatic...

If it's sucking harder than the rest and not spitting, (W/O checking the reeds), I would tend to agree a bad crank seal. It's pulling air Not from the carb but from the failed seal.

[TownsendsFJR1300]

[QUOTE=99yam40;n215383]So looks like this is a P50TLRQ,
I fail to see why that would be hard to post when you started this thread so everyone knows what motor you are talking about.
or when we asked several times for a model #

I am not familiar with one of these Solenoids, I have seen chokes and prime start systems, but I am not sure what this does since it looks like the same as the prime start,but the device is called a solenoid.
does it open a passage when you push the key in to allow extra fuel to be injected into the intake?
QUOTE]

I believe it's just typical Yamaha calling it a solenoid, which actually Prime start is, a solenoid that automatically opens.....

And, I too, guessed at the model # and used the same as you Yam99

[zenoahphobic]

This motor is a pro 50 2 stroke - 1992
it doesn’t have a choke , it had an enrichener - check out the picture

carb Is clean - soaked, blew air through passages and verified fuel in bowl

I can spray fuel in cylinder with no effect - it’s not the carb

I ran the motor yesterday, that’s why the plugs look like they do
it’s not fuel related
compression is right @ 100psi

i can cover the bottom carb when the motor is running, the motor will smoke and run rough

it’s not spitting fuel thru the carbs, but I can’t feel it pulling air like the others - upper reed on the stbd side has a different feel than the others

Bit of a contradiction when spraying fuel in has no affect yet covering the carb now will smoke and run rough. You started the thread by saying moving the carb (presumably opening that throttle on its own) had no affect?

[Freaky1974]

Spraying fuel @ idle has zero effect

running the motor, in the water on the boat - pushing the key in - the boat will accelerate just fine


that solenoid is fed fuel via the #3 carb - the solenoid pumps fuel in the manifold behind the carbs - it’s fuel enrichment , it adds fuel when the key is pushed

[zenoahphobic]

If I draw a line of best fit at diagnosing this fault, it seems that that cylinder is not burning fuel at all because it is overlean to the point that the mixture won't ignite.

The addition of fuel at idle should restore a "burning" mixture but it doesn't.

This can only be so if that cylinder can't "suck" air sufficiently, that is no matter what, there is only a small amount of combustible mixture drawn into the cylinder.

This can happen if there is a significant crankcase leak, like you suspect the crankshaft seal. The low sucking can also be the result of the lack of a combustion pulse out the exhaust and/ or interaction from the pulses of the other two burning exhausts. This is a two stroke and therefore significant reliance on pulse purging and charging, depending on the design, is a significant factor in it's functioning.

Now the enrichment seems to restore enough burning mixture to bring the engine to a point that it is pulse charging by itself, the air leak having less influence at higher revs.

You seem so certain that the issue has nothing to do with the carby, so my illustrated alternative view gives you some reason to pull that seal. I was sceptical because a leaking seal often causes water to enter, and that doesn't seem to be the case here.

You ofcourse should also check the reed valve, you should see it if that carby is off anyway now. A hole in the piston could also fit this scenario.

[99yam40]

Spraying fuel @ idle has zero effect

running the motor, in the water on the boat - pushing the key in - the boat will accelerate just fine


that solenoid is fed fuel via the #3 carb - the solenoid pumps fuel in the manifold behind the carbs - it’s fuel enrichment , it adds fuel when the key is pushed

my old 35 evenrude had something like that, even had a lever on it to operate it manually to squirt some fuel into the carb for starting if the electric part of it failed.
I did not know Yamaha ever had anything that.

sounds like it is running too lean if extra fuel helps, but only at higher RPM .
does the motor idle well?
might try spraying fuel mix into the individual carbs while out on the water under a load to find out which cylinders are being affected.

make sure the timing is in spec and advancing as it should also

[Freaky1974]

Pulled the powerhead just now

Seal housing for the lower crank seal was coated in black silicone - never a good sign

pulling the housing - it was filled with fuel. The o ring was split and the seal is sitting in the housing at an angle

pretty confident I found my problem

check out the pics

[Freaky1974]

[Freaky1974]

That o ring , it’s way small for the groove in the housing...


side note :

i purchased this motor as a completely rebuilt motor - I’ve had quite a few problems with it - but, I’m getting it sorted out

[panasonic]

Zeno called this one.

Glad you found your problem and I hope you don't find anything else on your engine done like that.

Is this the solenoid on your engine? It doesn't look like the typical Yamaha Prime start system with the extending needle that works automatically.

From your description of using the key it must shoot a shot of gas in each time you push it in. Much like an accelerator pump

[zenoahphobic]

I always have a problem when I hear something has been completely "rebuilt " because if you think about it is not possible to do such a thing unless you replace everything with new.
Your's is the example where a bit of inappropriate improvisation was used. Common hardware shop Silicon has no place where there is heat, oil, fuel and water immersion (except in gaskets or special applications like on space shuttle tiles and fish tank glass gluing).
It would be prudent that you strip the whole engine and renew whatever needs to be (should have been) done.