2006 90 hp 2 stroke Yamaha - Low Compression

[Retriever1]

Good evening! I have a 2006 2 stroke 90hp Yamaha...............so about a month ago, I hit an underwater obstruction, mechanic replaced the prop shaft / bearing, replaced the water pump etc., but indicated no additional damage to the engine. First time out, the engine ran well, but sounded a little different. This weekend, the engine stopped while running almost as if it ran out of gas, restarted and ran again for 10 minutes. Did the same thing again, however when restarted, sounded like it was knocking, rough and didn't have enough power to get on plane, towed back to dock.

Mechanic checked lower unit oil, it was fine. Checked compression and the #1 cylinder tested at 25, the other two were I think 105 and 110.

So my question, could hitting the underwater obstruction have caused what is described above? I find it almost too coincidental from a timing perspective.

Thanks in advance for your input!

Take care.

 

[Capt Ken]

Re: 2006 90 hp 2 stroke Yamaha - Low Compression

The striking could have caused some sediment to break loose in the #1 carb and lean out the cylinder by blocking the high speed jet.

 

[Toddboat]

Re: 2006 90 hp 2 stroke Yamaha - Low Compression

Capt. Ken,
Would that explain the low compression, though? A lean cylinder doesn't have to lead to compression as low as 25psi.
I think a more likely scenario is that the #1 cylinder isn't getting oil for some reason. Either that or it has a cracked ring.

 

[Retriever1]

Re: 2006 90 hp 2 stroke Yamaha - Low Compression

Thanks for the replys thus far............any additional thoughts. Compression was checked 9 months prior to hitting the underwater obstruction and the compression was perfect.

 

[99yam40]

Re: 2006 90 hp 2 stroke Yamaha - Low Compression

running a lean cylinder for some time will eat the piston,rings, and cylinder wall due to heat from lean fuel /air mix.

If any problem is felt , it is best not to run it to see if it gets better as it will end up hurting motor most of the time