[FUNCAT-YAMAHA]

I have a 2000 Yamaha 115 4-stroke.
It starts right up runs fine for a moment then begins to run rough and sometimes stall. It will not really rev up.

I started with the VST first cleaning them finally replacing it completely.
I had some questionable fuel so I am now running on a seperate tank with fresh fuel.

I noticed after unplugging the injectors one at a time it runs even worse with three different ones unplugged. With the fourth one unplugged it runs no different than with it plugged in.

How should I proceed?
Can I test if the connection is receiving a signal to operate the injector?
If there is electrical can I test if the injector is plugged and/or fouled and needs cleaning?
Should I be starting with the mechanicals of the cylinder? compression? valves?

I did not remove the plugs to see if there was a difference in them.

I would appreciate any suggestions.

[99yam40]

Check plugs, compression, then valves if you get bad compression.
You can test signal to injectors if you have proper equipment.
You might swap injectors to see if problem follows, but if you had bad fuel and you had to clean and replace VST then I would think you have plugged injectors or screens.