Yamaha 8HP running at low RPMs in gear.

[NSBW]

Hi, I?m new here so forgive me if I?m posting incorrectly. My Dads F27 Sail Boat has a 8HP Yamaha four stroke on it, I believe it is an 06?. I had a compleat service performed by a reputable shop in Fort Lauderdale eight months ago. The motor has had light intermittent use during those months. A week ago we dropped the boat in the water and I bought all fresh gas. We took a few sails and the motor ran beautifully. Then one morning it would not start. It took me a few tries to get her going but eventually I did. Now here is where the weird part is....
When in neutral the motor revs up to full RPMs. But when in gear under load I?m only getting maybe half RPMs. Normally the motor will push the boat at around 6.5 to 7 knots wide open. Now we only get 4.5 knots. But the engine starts fine and seems happy enough, no bogging or lugging or stalling. Just weak. It?s also weak in reverse.
Because we had a lot of rain I thought maybe the fuel had been so Howe compromised. So I started there.
1. Replaced fuel bulb and drained fuel lines and carb.
2. Replaced fuel connector on engine side
3. Replaced engine fuel filter
4. Removed and inspected fuel pump, spring felt strong, diaphragm and vanes looked good.
5. Checked that the throttle orientation was correct.
6. Removed Carburetor and dipped even though it looked clean. Put back on.
7. Checked plugs but did not spark test. Both looked clean.

I?m sort of at the end of my rope here. I?m starting to think it is an electrical issue. Any advice would be very helpful.

Thanks.

 

[99yam40]

compression, spark, and timing are all easy to test
if they are good then there is a fuel problem

 

[racerone]

Sounds like it is running on one cylinder.---Yes they will rev up in nuetral on one cylinder and that is not a good test.----Check for spark on both leads.

 

[Bonaventure]

Could the Propeller be slipping?

 

[tommarvin]

Sounds like a fuel problem, the motor runs sensors are working to run the motor, but the motor doesn't run well because it's probably starved for gas under load.
Make sure the fuel system is clean from tank to injectors, it's fast easy and cheap to clean fuel injectors and install a new filter on the fuel injector.

 

[GA_Boater]

Sounds like a fuel problem, the motor runs sensors are working to run the motor, but the motor doesn't run well because it's probably starved for gas under load.
Make sure the fuel system is clean from tank to injectors, it's fast easy and cheap to clean fuel injectors and install a new filter on the fuel injector.

Mr. Tom - Why are you obsessed with fuel injectors? This motor is carbed. Do you read threads before writing this stuff? Please only reply when you know what you are talking about.

Sorry NSBW . Welcome aboard and remember not all advice is good advice.