Yamaha 150 2stroke rpm issue

[marinetech345]

hey guys this is my first post but I have been on the forum reading posts for a while, recently became a marine tech and kind of stumped by this one.

Its a yammi 150 carb,not sure on the year. My supervisor wanted me to do a carb rebuild thinking that was the problem so i did that and reinstalled them today, not aware of the issue motor was having. So motor runs fine on the hose but once under load (in water) it wont get passed 2000rpms. Another tech that works with me checked the oil system thinking that motor was in gaurdian mode or something but there was no problem there. Any ideas ? im thinkin about doing the check myself tomorrow just incase he might have missed out something.

 

[99yam40]

Re: Yamaha 150 2stroke rpm issue

Is the compression good?
Test the alarm to make sure it works.
The safe mode will limit RPM by retarding the timing on most motors so A timing light will show that.
testing fuel supply and then the voltages at the problem RPM will help eliminate those as problems.
If all is good then it is back to the fuel and air ratio(carbs or seals)

 

[marinetech345]

Re: Yamaha 150 2stroke rpm issue

so checked compression, was between 125-130psi on all cylinders, checked oil system all was good, checked thermo switch which would cause rpm redection also and whati did notice today was motor had a lean sneaze, when pullin choke slightly out motor would rev a little better but would go to about 3000 rpm but no higher. Port bank of cylinders all look white (lean) and they were not really wet. starbord side are all brown. Got the story about this engine today though, the guy fogged the motor and it was layed up for a while, dont know why he did because it doesnt get cold at all here.Also the motor had ran completly out of oil on its last trip out. any idea ? thanks .

 

[99yam40]

Re: Yamaha 150 2stroke rpm issue

how did you check the oil system and the temp switch?
Did you see if the alarm works?
Are you sure there is oil getting to everywhere it needs to be?
I do not see how just one side would be affected on all 3 carbs.


If it laid up for awhile then the whole fuel system may need to be cleaned out.
You clean the carbs and then you push more trash into them from the lines and pump, not to mention the tank.

 

[marinetech345]

Re: Yamaha 150 2stroke rpm issue

checked to see if the alarm would come on when float on oil switch was at bottom,and it did also tested to make sure when float was at top, middle and bottom of switch that would get a continuity reading. For the temp switch i ran a jumper wire between the two wires and the alarm sounded then also, so alarm works. Thats the thing, i am confused as to why one side is affected. the boat has a racore fuel filter which was checked and wasnt dirty or any water in it also i checked the fuel filter on the motor which was pretty clean also. Fuel flow may be an issue here but why one lean bank of cylinders ? thanks for the help also 99yam40.