Yamaha 80hp, 4 stroke runs rough

[Capt dave 258]

Here's the history. recently bought this pontoon with a 2001 80hp, 4 stroke Yamaha. Knew it had an issue when I bought it. Previous owner brought it to a local marina and they said it needed the carbs rebuilt. After sitting at the marina for weeks without getting worked on, the owner went and brought it home. Motor will run but not get over 1000 rpms. Previous owner changed the fuel filter, gas lines, drained and added fresh fuel. Checked compression too and it was good. I bought the boat and duplicated their work. Again, fresh fuel, filter, and plugs. Did a compression test and results were from 190 to 200 on all cylinders. I found a local reputable independent mechanic. I removed the 4 carbs and he cleaned them, saying that they were a "little crusty". I put them back on and the motor runs better, able to achieve higher rpm's but the motor sputters and farts. Brought the boat back to the mechanic and he did a compression test and leak down test and all was good. He took the carbs off again and went through them and couldn't find an issue. Same problem, motor will sputter and fart. Both coils and fuel pumps were checked and all are good. Mechanic is scratching his head and thinks the next think to do would be to remove the valve cover and check valve lash. Any thoughts on a possible problem are appreciated. Thanks

 

[saltchuckmatt]

Here's the history. recently bought this pontoon with a 2001 80hp, 4 stroke Yamaha. Knew it had an issue when I bought it. Previous owner brought it to a local marina and they said it needed the carbs rebuilt. After sitting at the marina for weeks without getting worked on, the owner went and brought it home. Motor will run but not get over 1000 rpms. Previous owner changed the fuel filter, gas lines, drained and added fresh fuel. Checked compression too and it was good. I bought the boat and duplicated their work. Again, fresh fuel, filter, and plugs. Did a compression test and results were from 190 to 200 on all cylinders. I found a local reputable independent mechanic. I removed the 4 carbs and he cleaned them, saying that they were a "little crusty". I put them back on and the motor runs better, able to achieve higher rpm's but the motor sputters and farts. Brought the boat back to the mechanic and he did a compression test and leak down test and all was good. He took the carbs off again and went through them and couldn't find an issue. Same problem, motor will sputter and fart. Both coils and fuel pumps were checked and all are good. Mechanic is scratching his head and thinks the next think to do would be to remove the valve cover and check valve lash. Any thoughts on a possible problem are appreciated. Thanks

Yes, valve lash should be checked.