Pro 50 poor acceleration

[Freaky1974]

I’ve had a few problems with this motor. Problems with carbs was one situation , carbs are clean !

Heres the new situation:
appears the bottom carb isn’t working. I can turn the mixture screw all the way in and nothing happens. There’s fuel in the bowl. If I disconnect the linkage, the bottom carb does little when it’s linkage is moved. Other carbs react well.
that cylinder has 10lbs less pressure than the other 2.
im guessing I’ve a problem in the reed valves on that cylinder ??? I’m not suspecting a bad crank seal.

the poor acceleration - if I push the key in, the motor will accelerate well. Without pushing the key, it falls on its face.
seems worse when motor temp is warm .

Im guessing reeds ???

[zenoahphobic]

Maybe a broken reed but the carby will still work, it would spit some fuel out which would be quite noticeable.
If you don't see this "backspitting" then your earliest statement is incorrect, that carby is not clean.
Mr Townsend is good at lecturing on this subject.

[Freaky1974]

It’s not spitting fuel

I thought reeds, because of the difference in compression
carbs are spotless

[zenoahphobic]

It’s not spitting fuel

I thought reeds, because of the difference in compression
carbs are spotless

10 psi is not much difference (what are the other two?)
Two other reasons compression can be down.
If the carby hasn't been working your oil in the cylinder won't be dispersing properly, and/or the bottom seal is leaking water. Both will create greater wear and poor sealing of the rings.
I believe your carby is the culprit. You should be able to hear it if fuel is coming out and mixing with the air (straw sucking on the bottom of a soda drink), distinctly softer sound than from the other two if no fuel is being drawn.
However you have to be sure, and the look of that spark plug will tell you a lot. What does it look like and can a picture be posted?

[Freaky1974]

[Freaky1974]

The plug with my finger on it , that’s #3
doesnt look like it’s running on that cylinder

took the carbs off and took #3 apart - it’s clean inside
currently it’s soaking

doesn’t look like #1 was firing well either ?

[99yam40]

fuel pump leaking into #3 crankcase causing too rich fuel to air ratio for #3 to fire properly is a likely problem

[Freaky1974]

Nope - that’s not the problem

if it was the problem - adding more fuel , by pushing the key would make the condition worse, not improve it

[99yam40]

it is something that will affect #3 cylinder.
check the pump

we have no ideal what motor you have since you failed to tell us

and even if pushing the key does anything at all on your motor

ones with prime start systems and no choke the key does nothing

[Freaky1974]

Older Yamaha pro 50 2 stroke - motor has enrichment solenoid, not a choke

the fuel pump is new, a Yamaha part, not aftermarket
the mounting gasket was split and leaking previously...

[Freaky1974]

Here’s an update :

pulled the carbs and took #3 carb apart and soaked it
pulled jets and verified no debris - the carb is spotless clean and there’s no debris anywhere
reinstalled carbs, test ran
same situation - #3 carb is doing nothing @ idle and low rpm

i believe I have either a bad reed valve, bad lower crank seal
or a case leak somewhere ...

[pstephens46]

Here’s an update :

pulled the carbs and took #3 carb apart and soaked it
pulled jets and verified no debris - the carb is spotless clean and there’s no debris anywhere
reinstalled carbs, test ran
same situation - #3 carb is doing nothing @ idle and low rpm

i believe I have either a bad reed valve, bad lower crank seal
or a case leak somewhere ...

Sound pretty convinced of the three possibilities.
Let us know when you figure that sht out.

[99yam40]

Older Yamaha pro 50 2 stroke - motor has enrichment solenoid, not a choke

the fuel pump is new, a Yamaha part, not aftermarket
the mounting gasket was split and leaking previously...

exactly what is this enrichment solenoid you speak of.
and how old is an older yamaha
If you would give motor model # I could look at a parts diagram

[Freaky1974]

[Freaky1974]

Number 41,in that part diagram