2018 Yamaha 40 HP, Poor top Speed

[Laguna 20]

Took our 40 HP Yamaha into the dealer for a service, water Impeller/Fuel issue. Both problems fixed.

After running it in the water a couple of days we tried the Top Speed, it worked fine for a few minute then it sounded as if a Muffler fell off and reduced the speed. Not sure what happen but the boat still run great at slow/medium speed but the top speed isn't the same.

Any thoughts on what might have come loose or what I should check?

 

[airshot]

Took our 40 HP Yamaha into the dealer for a service, water Impeller/Fuel issue. Both problems fixed.

After running it in the water a couple of days we tried the Top Speed, it worked fine for a few minute then it sounded as if a Muffler fell off and reduced the speed. Not sure what happen but the boat still run great at slow/medium speed but the top speed isn't the same.

Any thoughts on what might have come loose or what I should check?

Needs to go back to that dealer as the problem is NOT fixed !

 

[cyclops222]

Something fell off / came loose.

 

[99yam40]

need to talk about RPM also, not just speed

 

[racerone]

Spun the prop ?----Motor mounted too high ?----What kind of boat?

 

[cyclops222]

My prop slipping was a piece of rope around the prop.

 

[Laguna 20]

Spun the prop ?----Motor mounted too high ?----What kind of boat?

Spun the prop ?----Motor mounted too high ?----What kind of boat?

Spun the prop ?----Motor mounted too high ?----What kind of boat?

The Boat type is a Novurania Dinghy 14', the main repair we did was the fuel system. Fixing the fuel did add speed to the boat which could have caused the Prop to have spun.
The motor height seems fine as it's a short shaft motor that matches the transom height.

How do I check for a spun prop?

Thanks for your response.

 

[99yam40]

mark the prop and hub/shaft.
run the boat to make the problem happen again and then check to see if the marks are still lined up

 

[Laguna 20]

need to talk about RPM also, not just speed

Checked the prop, it's good. the RPM is only coming up to about 3500. Checked the travel on the throttle and it is traveling the full distance allowed.
Motor doesn't sound like it's missing.

The boat is a 14' Dinghy with a hard bottom.

 

[racerone]

Running on 2 of 3 cylinders ??-----Should be easy to figure out the total lack of performance.-----Post actual compression values.----Does spark jump a gap of 3/8" on each lead ?

 

[99yam40]

Took our 40 HP Yamaha into the dealer for a service, water Impeller/Fuel issue. Both problems fixed.

After running it in the water a couple of days we tried the Top Speed, it worked fine for a few minute then it sounded as if a Muffler fell off and reduced the speed. Not sure what happen but the boat still run great at slow/medium speed but the top speed isn't the same.

Any thoughts on what might have come loose or what I should check?

what does this mean .sounded as if a Muffler fell off
exhaust goes out the prop under water so it should be not loud.
maybe the motor is too high and the sound comes out above the water

 

[Laguna 20]

The motor was running fine at full speed right around 5K RPM, while driving it made a noise "as if" a muffler fell off and drop speed. when looking under cowling everything looks fine.

 

[Laguna 20]

Running on 2 of 3 cylinders ??-----Should be easy to figure out the total lack of performance.-----Post actual compression values.----Does spark jump a gap of 3/8" on each lead ?

I'll check compression and spark and follow up. Thanks

 

[99yam40]

you need to figure out where that loud noise is coming from
and does the RPM slow down also or just the speed is reduced?

 

[airshot]

What did that dealer fail to put back on and retighten?? I would let th m figure it out !