86 Yamaha 40hp sputter

[BNflyfish]

I have a 86 yamaha 40hp that has new water pump, fuel lines, fuel tank, and clean carbs. It idles great and accelerates great, but after it reaches about 3200 rpm it starts sputtering/chattering and drops off rpm. Anything below the 3200 rpm/half thottle and it runs OK. I have a service manuel but would appreciate greatly any ideas on where to start looking. Thanks

 

[JUSTINTIME]

Re: 86 Yamaha 40hp sputter

how did u clean the carbs?

 

[BNflyfish]

Re: 86 Yamaha 40hp sputter

I actually had the carbs "cleaned" by a retired marine mechanic. He seemed to think the sputter/chatter has something to do with the electronics. It idles really smooth and thottles up clean and will run top end for about 3-5 seconds before it begins to sputter. It also runs fine up to half thottle. I also just found a piece of small hose lying in the bottom underneath the carbs. It looks like a piece of vacum hose, about 1/4" dia., with a plug on one end and a broke off plastic connector on the other. I don't see where it goes but that might be the cause of the problem. I will look harder and if I still don't see where it goes I'll try to attach a digital pic. Thanks again.