Yam 50 looses power

[deanc777]

Yamaha 50 hp 99 2stroke problems please help..
when out on the water outboard will loose speed from full revs down to about 4000 rpms or even less this will happen randomly sometimes after 15mins or straight away or sometimes not at all. It could stay like this for 15minutes or 30 seconds then it will go back to full revs. Alarm buzzer doesnt sound oil level has been checked Fuel tank has been cleaned spark plugs have been replaced also been serviced and they informed me that there was nothing wrong when they tested it in the tank. I dont know much about outboards but there is two lines on the cdi unit and when you push the foward control fully foward the linkage goes past the line maybe this needs adjusting.PLEASE HELP its getting very frustrating not knowing if its going to happen next tkme i use it.

[Ken]

dean,
Next time this happens, try squeezing the primer bulb to see if that makes any difference.
If the motor returns to full rpm, then you have a fuel starvation problem. Check fuel filters - fuel pump - all connections from carbs to fuel tank.
If fuel tank has anti-siphon valve, check it - they can cause intermmitent fuel restriction problems.
Good luck,
Ken K

[deanc777]

thanks ken have tried all of that except replacing fuel pump. it seems as if it only runs on two cylinders when it loses power and when you pull the control back to netural it coughs sometimes and idles rough. Can it get to much petrol and cause this??

[Ken]

dean,
If that 50 hp Yammie has never had a carb rebuild, I would do it. It just may fix your problem - needs to be done anyway - your motor is six years old - needs to be done about every five years. You could be experiencing float problems on one of those carbs, or effects of gum/varnish buildup.
Good luck, and let us know what you find out.
Ken K

[deanc777]

thanks ken you said carb rebuild. The motor had only done 90 hours work in 5 years and about 80 in the last year since i brought it. as i dont know much about outboards would a carb rebuild be necessary?? Or is there something i can run thru the fuel line and carbs to clean them if they are gummed up without taking them apart?

[Bobbyr]

Dean , Ken is rite clean carbs, take them off and clean them and check for any worn parts. Also very low hours on a 2 stroke is not neccsary great ,the need to be run.

[Ken]

dean,
Yeah, even a brand new outboard with one hour on it will give you problems with gummed/varnished carbs if allowed to set up for months at a time without being run.
If you want to try the easy way first, do a shock treatment with Seafoam (scroll down thru my posts where I describe the procedure). That may clean out the fuel system enough for you. If that doesn't do the job, then remove the needles of the jets of the carbs and squirt Berryman's Chemtool into the seats. Sometimes that will clean out any gum/varnish in the jets.
If none of the above works, then carb teardown and rebuild is in order.
Good luck,
Ken K