Question on F300 Offshore for Experienced Yamaha Mechanic...

KMango

Recruit
Joined
May 18, 2016
Messages
2
Ok...took the boat out to run through my winterized gas and check things out and noticed that when first hitting the throttle, before the boat goes on plane, I hear a rattle type sound coming from the front of the engine. Once the boat is on plane and running...engine sounds good. Only ran it between 3800rpm and 5000 rpm, mostly 4500 rpm, as I am just running out the winterized tank. I did at 12 gallons of premium to mix up and increase the octane of the stored fuel. Boat was stored in the garage from October until May....non heated garage.

Couple extra pieces. I did not notice this upon initial start up or initial thrust when putting the boat on plane nor did it happen when running it for like 40 minutes to 45 minutes straight adjusting the rpm up and down every once in a while. The first time off plane, however, then back up on plane again I started noticing it. So the engine was warmed at idle, fine while running, but once heated up good...then it started but only on initial full throttle thrust until boat planes.

Let engine cool by running the kicker for a while and checking electronics, front motor, live wells, etc., about 45 minute, then on initial startup, full throttle to plane, didn't really hear it. But after it was run awhile, from still position, full throttle up to plane heard the rattle again. Can also get a little bit of it when out of gear in neutral, reeving the engine....starts about 2100rpm. BUT much more apparent under load to plane.

Engine is a Yamaha F300 Offshore, dealer winterization every winter, boat stored in garage with 1/2 tank premium fuel...again... fully winterized, never any water found in fuel/filter water separator (as of yet)....and I change them twice a year, run Yamaha Ring Free and Yamaha Fuel Conditioner/Stabilizer per continuous running instructions religiously. Plus, power and thrust seems normal to plane and running speeds seem same as previous years. Engine is on its 4th season with about 140hrs on it.

First thought....low octane and noise caused by engine nock....but just a guess. Weird that it doesn't happen at 3/4 to full throttle and more in the midrange at the time when there is the most load on the engine. Sounds similar to the ISC timing advance one hears when first starting the F300....you know....that quick rattle....but not quite the same.


Any ideas????
 
Last edited:

tommarvin

Ensign
Joined
Nov 22, 2015
Messages
999
I don't know if this is enough of a problem to show something on YDS diagnostic software.
You could have dealer run the diagnostic software just to be safe.
 
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