1987 175 yamaha

[pantera1929@yahoo.com]

I have an issue with a 175 yamaha on a 1987 ranger 373v. The engine starts and idles fine. When throttle is applied in neutral it revs fine, but when put under a load it never gets up to speed. I was wondering what could be wrong. I checked fuel pumps. They seem to be ok. Carbs seem to be clean. I tried running seafoam through the system and nothing. I also checked to make sure we were getting spark to all 6 cylinders and I am. Where would be a good place to start trouble shooting from here?

[boats.net]

Check compression. Most of the time it's dirty carbs or fuel restriction, could loosing ignition to one or more cylinders.