HPDI 300 excessive bubbling

[Edselectric]

I have a 2004 HPDI 300 that I recently purchased. I just took it out for a test run and it seems like the exhaust is coming out of the mid section somewhere.

The mid section also gets very hot...too hot to touch and there are a lot of bubbles.

I've seen some posts about an exhaust tuner but I cant find it on a parts list and I don't know where to look for it.

Any help would be appreciated.

[pstephens46]

Maybe Rodbolt can help...

I remember your post on THT.

There was another guy on here with a 200 HPDI with the same issue. The last we heard he was trying to get the boat hauled in order to drop the lower to have a look....haven't heard back.

[99yam40]

I am sure the power head has to come off
Maybe it is called a muffler

[pstephens46]

I am sure the power head has to come off
Maybe it is called a muffler

Maybe it can be scoped first.

Edselectric also had a video he posted on THT. Showed the bubbles and
steam out of idle port. Just like the other guy.

[Edselectric]

Thanks guys, Yes I did post in the THT but I'm not getting much help over there.
In the video I was more concerned with the steam coming from the upper exhaust. This was fixed when the poppet value was replaced.

I didn't know the bubbles were an issue until someone mentioned it in their post.
Now after doing some research it seems a though there is an issue with the exhaust tuner.

I have looked up the mid section and I don't see anything that looks melted or broken.

I hope I don't have to remove the powerhead to get to it.

This is the video, it only bubbles like that once its hot.

https://www.youtube.com/watch?v=XU9tgSpH4uM

Thanks

[rodbolt17]

drop the gearcase.
find a tech with a snap-on BK6000 or similar.
then you can take pics or video of the tuner.
my scope can see straight or 90* and does pics,video and audio.
careful with the audio.

[99yam40]

Is the tuner the exhaust manifold, or the muffler?
2004 VZ300TLRC Yamaha Outboard UPPER CASING Diagram and Parts

[Edselectric]

drop the gearcase.
find a tech with a snap-on BK6000 or similar.
then you can take pics or video of the tuner.
my scope can see straight or 90* and does pics,video and audio.
careful with the audio.

Would a bad exhaust tuner cause those bubbles?

It only happens when it's hot

[Edselectric]

I removed the lower and looked inside and everything looked fine,

I removed the powerhead and everything looked fine, no signs of exhaust leaking, the muffler looks to be in 1 piece with no holes.

The one thing that has me thinking the issue may be somewhere else is because there are no bubbles when its cold.
I haven't tested it yet but I'm thinking the bubbles are coming from the slots on the side of the lowerunit where the water would come out once the thermostats open.

If this is the case, what could it be?