1991 Yamaha VX76 250hp Carbed model

[tiiim]

Hi,

I have a Yamaha 250hp that is limited to 22mph. Its been like this since I got it. The oiling system was removed when I picked it up. So it has to run on premix. It starts and runs fine but when you go WOT it goes then drops down to 22mph. Compression is fine. Any ideas on how to bypass what is causing this error I assume its computer related. Thanks!

 

[Chris1956]

I doubt a 1991 motor has a computer. Check to see that the carbs open and the spark advances. Both are usually manual linkages.

 

[99yam40]

check compression on all cylinders, while you pull the plugs see if one or more looks different than the others.
check to see if fuel pumps are working properly and not leaking into the crankcase causing too rich of mix to just some cylinders.( this is my 1st thought of your problem)
it is a good idea to replace the pumps every few years.
drain the carb bowls and catch what comes out to see if water or other things are floating around in one or more of them.
can also check timing to see if it is changing when the RPMs drop or if spark is dropping to one or more cylinders