Bought SJ...plugged inlet/outlet from head to exhaust?

M

mazur

Location
Mesa, AZ
Hey guys,

I tried to search for a clear answer, but most topics I find don't provide much details to how the exhaust system works (I'm new to both two-strokes and marine engines) and why diverting water from the pipe helps with performance. Apparently most are not starting from dummy level like me.

I just picked up a 95 sj and noticed that the water line going from head to pipe is disconnected and plugged (image of missing hose below). I read that some people divert some of the water to improve performance, but never completely. I think I want to reconnect because I cannot imagine this is good long term, but I don't fully understand what that water is doing, or even what the function of the waterbox is and if that component is even affected by this mod.

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S

SquarenoseSj701

Location
Sacramento
I believe that hose is meant to allow air to escape the cylinder head water jacket. Notice that it is at the highest point of the head when riding. If you allow all the air to escape from the highest point, then you ensure that water fills the jacket entirely.

Also before the water jackets fill up with water that line can flow the opposite direction from exhaust pressure (similar to how you may have exhaust coming out of your pisser before the jackets fill up). I once broke that hose putting my hood on and my ski ran like crap, acted like I had an exhaust leak until it cleared out
 
S

SquarenoseSj701

Location
Sacramento
... but after the initial startup, it's just a secondary water line transporting hot water from your head into your exhaust.

The majority of hot water from the head goes out the fatter water hose on the other side of the head, that water fills the exhaust water jackets including that rubber boot and the big metal box that says Yamaha on it.

FYI, your "water box" is at the very front tip of your superjet. You have to remove the gas tank to find it
 
M

mazur

Location
Mesa, AZ
OK, that clears some things up for me, but the fact that line could act as an air purge line makes a lot of sense and makes me assume I may have bought the ski from a jackass who didn't know what he was doing, but hopefully didn't cause any damage. I odn't think a 4-stroke would last long with air trapped in its cooling passages.

I know where the waterbox is, but I don't get what it does. Is it just a silencer/muffler?
 
S

SquarenoseSj701

Location
Sacramento
Yea I dont know how critical that line is, but Yamaha put it there for a reason so i would hook it back up

I believe that is correct that the water box is just a muffler. Maybe it is supposed to provide slight back pressure too? Im not too sure
 
bored&stroked

bored&stroked

Urban redneck
Location
AZ
The water box is after the pipe and in front of your gas tank. On the SN it is fiberglass and boxy in shape. It acts as both a muffler and a way to keep water from going up the exhaust and into the engine.

Diverting water from the pipe means less water is injected into the exhaust stream to cool it down. The by product is more power. You can reduce water injection amounts until the pipe gets too hot or the rubber hoses start melting.
 
S

SquarenoseSj701

Location
Sacramento
That hose OP asked about diverts water from the exhaust water jacket but it still goes into the same exhaust stream. So there would be no difference in power when that hose is reconnected...

Unless you were to send that water overboard via a pisser, but that's a pretty small line for a pisser
 
M

mazur

Location
Mesa, AZ
bored&stroked said:
My old hood. I'm recker and brown ish.
Click to expand...

Pretty damn close!

*Off-topic:

I guess there is no private messaging on this board? Or maybe I do not have permission yet. Anyways. If you're ever at Canyon Lake and I am around, I'd love for you ride my ski and see if all seems right with it. For example, I feel like it porpoises a lot, but I have read this could just be rider error and have had moments where it goes away. At first I thought it was just due to riding slowly in chop my first couple days, but I went out yesterday in relatively smooth water and I was still porpoising and felt like the ski had weak hookup when I tried opening her up. I also noticed that my pump and ride plate are already shimmed down (i have a worx grate and dominator ride plate). Most of this is predicated by my experience with my GP1300R and how well that ski hooks up and handles chop.

I don't currently know anyone else with a standup. :/
 
bored&stroked

bored&stroked

Urban redneck
Location
AZ
I avoid canyon the cops are dicks there unlike every other lake in AZ.
Im always at saguaro or bartlett. Bartlett has the beach usually and its nice to just back the skis into the water and leave the truck there and hang out all day.

You should not have handling issues with those aftermarket parts. You on facebook? Phoenix Jet Sports Association is where all us standup guys talk.
 
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