1988 50HP - Dies under load

[Kensterling]

Hello,
I purchased an old bass boat with a 50 hp Yamaha oil injected motor. The motor starts and runs OK...will run the boat about 5 MPH, but when additional throttle is applied and the motor has load, it dies..
The carbs have been checked and it has new plugs and new fresh gas....can't find any obvious electrical problems.....any ideas on this old motor?
When it is idling it sounds good and seems to run smooth.

Thanks
Ken

[boscoe99]

Just about the time that it starts to die mist some gasoline into the air intake system. See what happens. Report your findings.

[99yam40]

what does carbs have been checked mean?

I would bet on main jets have a problem.
BIL had a similar problem with his 50 and all I could find was #3 main jet was restricted.
cleaned and that fixed it

[ausnoelm]

Clean carbs properly, not sprayed or miracle additive in the fuel, make sure the timing is advancing with the throttle, check spark on all cylinders all the time.

[Kensterling]

Thanks for the replies! I have ordered Carb rebuild kits and will go through all three carbs....I suspect that will be the fix for the problem....I will report when completed.

Ken

[ausnoelm]

Yamaha carbs are very hard to clean properly, every fuel/air passage must be clean, including in the carb bodies, simply washing or spraying cleaner will NOT clean them out.

[panasonic]

Thanks for the replies! I have ordered Carb rebuild kits and will go through all three carbs....I suspect that will be the fix for the problem....I will report when completed.

Ken

Do your self a favor and buy a cheap ultrasonic cleaner on Amazon. You will only have to remove, disassemble and clean them once.

[99yam40]

do yourself another favor and open them up and inspect the main jets, may not need kits unless some of the seals are not reusable.

The bottom carb tends to be the one that extra stuff ends up in the bowl when all the fuel evaporates.
may just need to make sure all the bowls and main jets are cleaned up if it idles well.

make sure you follow the link and sync procedure in the service manual after you put the carbs back on

[Keithbaja]

A link and sync isn't that critical. Trust me on that..I done 1000's of carbs

[Kensterling]

Mystery solved with compression test
Middle hole = 15# of compression......top and bottom = 100#
So I have a large boat anchor!

[99yam40]

Mystery solved with compression test
Middle hole = 15# of compression......top and bottom = 100#
So I have a large boat anchor!

inspect and see what it would take to repair.
find a powerhead maybe
or see about selling it for parts if it is too much for you to handle

have you checked the fuel pump to see if it was dumping raw fuel into #2 crankcase?
might have washes oil off the cylinder walls and piston.
shoot some 2 stroke oil into the plug hole and re check the compression.

hard to believe it would idle well if #2 had that bad of compression.

[brian3006]

inspect and see what it would take to repair.
find a powerhead maybe
or see about selling it for parts if it is too much for you to handle

Agree. they are pretty simple motors, if you are any type of mechanically inclined.

those old 50's and 60's are pretty common around here. maybe you can find donor motor for cheap...or just a whole new motor if the price is right.

Can you see any damage through the spark plug hole?