F50 with jet- Runs at 80%

[YamiJet]

I have a Yamaha F50 with a jet leg and looking for some hlp to diagnose a problem.

The motor seems to bog a bit and not run to its potential half the time. It will on its own all of a sudden start to run properly and gain approx. 5-6 mph as I hear the engine start to run good. Then it will start to bog again and slow down, all without touching the throttle. This is very inconsistent, and seems to run the best after the motor has been run for a half hour or so.

When it runs good (20% of the time) it pulls hard as it should

I have had the carbs balanced, checked the timing and all is in spec. I have also changed the plugs and it made no difference.

I am currently running some fuel system cleaner through the engine.

I suspect there must be some crap floating around in the carb bowls?

The inconsistency of this problem has me stumped!

any help would be appreciated.

[boats.net]

Could be dirty carbs or loosing ignition on one or cylinders, start with removing and cleaning carbs and resync.

[99yam40]

an inductive timing light hooked to the different plug wires should show you if you are loosing spark to certain cylinders while problem is happening, and also tell you that the timing is doing what it is suppose to.

[YamiJet]

Thanks for the troubleshooting tips.

Today I ran some seafoam through and I will let it sit in the carb bowls overnight.

If this does nothing I will remove and clean carbs.

[99yam40]

Running a cylinder lean will cause major piston problems, so do not run it that way long