2002 F50TL 4 stroke Yamaha misfire/ starling

[HelixBoat]

Hello,
Model: F50TLRA
I just purchased a Fisher 16ft with a 2002 Yamaha 50HP 4 stroke, lower hours. Was driven last year and stored since then.

The motor idles perfectly fine. When put into gear it would almost stall out, as you throttle it up, it sputters.

You can find a sweet spot and it gets going. It will run fine at full WOT but all of sudden the rpm will go from 4500 to 3500. It almost sounds like it running of two cylinders. Valves sound a little load when this happens.

You back of the gas and let it sit for a while it run at full wot for a bit again then sputter down again.

Any ideas, I may bring it into the shop? The motor has 55 hours it. I bought the boat, motor and trailer for $4700 cdn.

 

[99yam40]

does this rig have a tach to show if alarm is happening?

Kind of doubt it is running at those RPMs.
does it have fresh fuel or is it still some of the old stuff?

probably needs carbs gone thru.
have heard that motor has a lot of strange fuel set ups

 

[HelixBoat]

It does have a Digital Yamaha TAC with low oil, and overheating. No alarms. It had some older gas maybe, but we filled the 25L tank with 17 litres of premium fuel. I am thinking the carbs need to be cleaned

 

[HelixBoat]

Well took a closer look today and realized the owner had the gas line backwards. I am thinking that may be the culprit