Weak AUX Exhaust- Excessive Bubbles- Yamaha F300

[Greatmojo]

2018 F300XCA- 1100hrs. The exhaust from the auxiliary exhaust port is weak and there are an excessive amount of bubbles in the water. This just started, no performance-related issues. Can someone tell me what causes this and how to resolve?

Video here: https://www.thehulltruth.com/boatin...cessive-bubbles-yamaha-f300.html#post15809575

 

[Halfhitch]

At idle that exhaust port should be active but should not be below water constantly. Has your boat recently started sitting deeper in the water than before?

 

[Greatmojo]

At idle that exhaust port should be active but should not be below water constantly. Has your boat recently started sitting deeper in the water than before?

Nope. This video is at idle.

 

[Halfhitch]

Maybe I misunderstood what I was seeing in that short video. I thought that load of bubbles was due to the idle exhaust port being submerged and the idle poppet was releasing exhaust due to idle speed.

 

[Greatmojo]

Ah got it. The idle exhaust is not submerged. The idle poppet is “weak” in comparison to the port engine and seems it’s releasing it below the water. Here's a longer video showing the comparison of the two engines: https://youtube.com/shorts/y8gZNL5fSQs

 

[Greatmojo]

Problem solved. Salt build up in idle exhaust. Cleared it out- problem solved.

 

[seasick]

That's a lot of buildup. Have you checked your t-stat chambers?
Do you fresh water flush after use?
Do you boat on the Great Salt Lake?

 

[Greatmojo]

T-stats are brand new. Chambers looks great and I always replace the t-stats every 300hrs regardless of how they look and flush with salt away after every use… I’ve never shot the hose in this idle exhaust boot though, but I’ll certainly be doing that moving forward. I’m told this build up is a product of 100’s of hours trolling in hot/humid weather (mostly in south Florida & Bahamas) , but who knows…

 

[seasick]

Thanks for the info. It's good to know..
I am happy that it was that simple.
When I read the post, my first thought was an exhaust leak due to corrosion or a bad gasket

 

[Sardinia306Bimini]

T-stats are brand new. Chambers looks great and I always replace the t-stats every 300hrs regardless of how they look and flush with salt away after every use… I’ve never shot the hose in this idle exhaust boot though, but I’ll certainly be doing that moving forward. I’m told this build up is a product of 100’s of hours trolling in hot/humid weather (mostly in south Florida & Bahamas) , but who knows…

Ha!
I have exactly the same problem with my 2019 F250, salt builds up between exhaust and the black silencer/water trap box and all exhaust gasses escape on lower unit.
Cleaning the salt buildup at 100hr service and all is good but 30 hours later it start again till quickly idle exhaust is completely clogged.

Does not seem to be a problem, as technicians said same; comes from long idling and low speed trolling.
However, the noisy bubbling at idle drove me nuts, now I am used to it.

Never had that an any outboard I owned.

Good to know that I am not alone ...

Chris