1990 yamaha pro 50 stalls

[mdawson28]

i have a pro 50 2 stroke motor 1990 after about 2 minutes it stalls out .
have taken it to yamaha dealer and got the carbs cleaned does same thing it
doesnt seem to be running on bottom plug.Compression is 120 on all three.
have try replacing plugs same outcome.
have spark on bottom also
replaced head gasket also
starts fine
when pulling spark plug wire off it doesnt do any thing on bottom plug on the
top 2 it kills the motor.

any advice would be great!!
Thanks

 

[99yam40]

Re: 1990 yamaha pro 50 stalls

Have you pulled and inspected or replaces the fuel pump?
Could be it is leaking and flooding the crankcase on # 3 cylinder

 

[mdawson28]

Re: 1990 yamaha pro 50 stalls

no i havent was told buy the tech (yamaha) that the crank case lower seal was the problem possible !
does that sound possible . got it out in 20 min they wanted 5 hours to do it ....
there are 3 seal an o ring and a bottom gasket will try thise first then wait and see

 

[jeffersondodson561]

Re: 1990 yamaha pro 50 stalls

Definately, find the fuel pump on the engine, is it close to the #3 cylinder? In my oppinion, the fuel pump should be included in the estimate for the carb overhaul. I have never done one where I did not rebuild/replace the fuel pump on a two stroke.

 

[J J Healy]

Re: 1990 yamaha pro 50 stalls

Finally found someone with the same situation.. my '89 130 has the same issues, i popped the pump and it seemed ok, but the gasket to the block couldve been a little over compressed. I'll try a new one. Here is one question. Could that pump issue lead to extra oiling, or excessive oil in the exhaust??? My barrel water has quite a slick on it, and it seems to be extra smokey whilst running real crappy, before stalling... will go for pump(again) in the meantime... ps how did the lower seal job go?

 

[mdawson28]

Re: 1990 yamaha pro 50 stalls

im a toyota tech it took me 25 min to remove
hardest thing to do was get the crank seal cover out need a couple of guyd to hold motor
i did remove the engine completely
picked it up to clear shaft then tilted it foward

 

[jeffersondodson561]

Re: 1990 yamaha pro 50 stalls

That is a good indication of a torn fuel pump diaphram. What you are seeing is a sheen from the fuel not oil.

 

[mdawson28]

Re: 1990 yamaha pro 50 stalls

its runs fine at full throttle or at least on 2 cylinder no back firing or choking
it only seems to be problem at idle ...
still think its a fuel pump issue??

 

[J J Healy]

Re: 1990 yamaha pro 50 stalls

Easy enough then. Im ordering a new one now. Thanks for the help, makes sense to me....

 

[jeffersondodson561]

Re: 1990 yamaha pro 50 stalls

Don't forget the gasket too, if I remember correctly you have to buy it seperately.

 

[99yam40]

Re: 1990 yamaha pro 50 stalls

its runs fine at full throttle or at least on 2 cylinder no back firing or choking
it only seems to be problem at idle ...
still think its a fuel pump issue??

There is no 3 cylinder motor that can run fine at WOT on only 2 cylinders

 

[mdawson28]

Re: 1990 yamaha pro 50 stalls

changed the crank seal still same thing
if you idle the motor up some it runs if you pull off the #3 spark plug wire its doesn't change its rpms
if on idle it up it stays running
if not it dies after 2 minutes approx then starts up not problem
moved coils same thing
i checked compression my self 110 across the 3 cylinders
as it idled i pumped the primer ball it still died out after 2 mins approx same condition
PLEASE HELP ME !!!!!!!

 

[99yam40]

Re: 1990 yamaha pro 50 stalls

have you checked the fuel pump like we said yet?

Sounds like carb problems still if fuel pump is not a problem

 

[jeffersondodson561]

Re: 1990 yamaha pro 50 stalls

changed the crank seal still same thing...

What the hell are you doing?

 

[mdawson28]

Re: 1990 yamaha pro 50 stalls

Took to local yamaha dealer they removed carbs and cleaned them they didn t touch the fuel pump
They told me it was a crank seal problem they tough so i replace it ....
Would a fuel pump allow the motor to run just of idle speed

 

[jeffersondodson561]

Re: 1990 yamaha pro 50 stalls

Why would they say to replace the lower seal? Each cylinder is sealed from one another by labrynth seals. The seal just keeps oil in the crankcase. The fuel pump is powered by the pulses from the upward and downward movement of the piston. These diaphrams are really thin and subject to wear and deterioration. Look I know that you are a Toyota tech, but their is a difference between the nomenclature of the parts on the engine. If I said the water pump was bad you would probably replace the water pump on the engine. To us, the water pump is referred to the circulation pump, water pump to us is called impeller or sea water pump. I don't know if you have any experience with 2 strokes. But if I was to explain the theory of operation to a person who did not understand internal combustion concepts vs. to a person who just knows 4 stroke operation, chances are the person who knows nothing about engines would pick it up quicker. That being said, their is a hole in the sealed crankcase of the #3 cylinder that powers the FUEL PUMP. If that diaphram becomes damaged, raw fuel can enter the sealed part of the crankcase making the fuel air mixture too rich. Depending on the size of the hole, and it is only going to get worse, it can cause more of a problem at idle than WOT. I am not saying that the fuel pump is the definate problem, but we can only tell you so many times to check the fuel pump!

 

[mdawson28]

Re: 1990 yamaha pro 50 stalls

I replaced the fuel pump today
Same thing
Is there specs on the CDi unit like volt and resistance
Is there resistance specs on the coil pulsars
Or where you you go next
W
Swapped the coil 1 for 3 no change
Or other things that I can check
Swap the coil pulsers

 

[99yam40]

Re: 1990 yamaha pro 50 stalls

kind of sounds like you are working on this thing with out the Yamaha service manual for your motor and may not have the proper equipment to test then inputs and out puts of the CDI of an outboard motor.( peak reading meter or a DVA adapter with a regular meter)
It would be best to follow the steps in the manual and make sure there is the proper peak voltages being generated into and coming out of the CDI. But you told us it had good compression and spark, so how knows what is going on.

 

[mdawson28]

Re: 1990 yamaha pro 50 stalls

for sure has good compression 110 psi ALL THREE
CARBS REBUILT AND BALANCED and changed fuel pump brand new.....
moved coil pulsers around still same thing spark there nice big jump across the the spark tester....all cylinders
after moving pulsers and back to original places the hole time # 3 plug doesn't change when removing the spark plug wire off

 

[mdawson28]

Re: 1990 yamaha pro 50 stalls

noticed on the #3 carb is the choke solenoid could this cause this problem
have a Fluke meter and a amp clamp and oscilloscope and can use them and back probe properly
no i don't have a manual but can test what ever you tell me too. just need wire colours and specs.or a wiring diagram
thanks for the help so far.