2004 Sugar Sand Mirage 1800 / Sport Jet 175 Cavitation or Ventilation?

[jrastama]

I bought a used 2004 Sugar Sand Mirage 1800 with the Mercury Sport Jet 175 in it. Initially ran good early spring but lately having some issues. Had it in to the mechanic to have the carbs rebuilt. He said compression and spark are good. The tachometer was also bad so I replaced that.

The current issue is that the boat seems to be cavitating or potentially ventilating. I often have issues getting up onto plane. The RPMs seem to want to go over 5,500... I can cruise at about 80-90% throttle but the RPMs are already above 5,000 and only going about 30-35 mph. If I try to go beyond that the motor starts to bog down.

I know my stator vanes are worn, but could that be causing this big of a difference? The impeller and wear ring look OK to me. Could use some improvement there too but feel like I should be getting more out of what I currently have.

I'm a bit concerned that exhaust may be leaking in along the drive shaft. Looks to me like that's the only place it could get in the way. Just not sure how to further test/diagnose that if it is a potential issue.

Took some pics today for reference. Any advice would be greatly appreciated!

 

[Bilmon]

You are cavitating. Doesn't take much wear to cause it, it will be more noticeable when accelerating. Stator doesn't look bad, mine is far worse [ 03 Mirage 240 ]

 

[jrastama]

You are cavitating. Doesn't take much wear to cause it, it will be more noticeable when accelerating. Stator doesn't look bad, mine is far worse [ 03 Mirage 240 ]

So, if I'm understanding you correctly, it sounds like the impeller and/or wear ring are worn and there is too much of a gap between them.

I'm new to these boats but I have seen some comments about replacing the impeller and/or wear ring with stainless steel I believe to make them last longer. I'm currently in-season so ideally don't want to send the parts in for reworking until later in the year. Looking for the best quick fix to keep me running until the offseason. Would it make sense for me to start with replacing the impeller and go from there?

 

[Bilmon]

Yep, too much gap and it feels like a slipping transmission. You can coat the wear ring with JB weld and likely get though the season, just don't cover the cluster of small holes, they are the engine cooling intake. You can have the impeller rebuilt, it's already stainless, and the aluminum wear ring can also be sleeved with stainless. I have my original impeller and wear ring I keep meaning to send out but can't seem to get around to it. I'm the original owner and have only changed them out once, they seem to be pretty durable, I have run in a lot of very shallow water over the years and run aground more times than I like to admit.

 

[jrastama]

Yep, too much gap and it feels like a slipping transmission. You can coat the wear ring with JB weld and likely get though the season, just don't cover the cluster of small holes, they are the engine cooling intake. You can have the impeller rebuilt, it's already stainless, and the aluminum wear ring can also be sleeved with stainless. I have my original impeller and wear ring I keep meaning to send out but can't seem to get around to it. I'm the original owner and have only changed them out once, they seem to be pretty durable, I have run in a lot of very shallow water over the years and run aground more times than I like to admit.

In order to try the JB weld trick, I need to pull the impeller with the special Mercury socket (p/n 91-850297), correct? No good way around that? $130+ for a socket is a bit tough to swallow at the moment.

 

[jrastama]

In order to try the JB weld trick, I need to pull the impeller with the special Mercury socket (p/n 91-850297), correct? No good way around that? $130+ for a socket is a bit tough to swallow at the moment.

Actually, I found a 1-7/8-inch socket that is 5.5 inches deep for $27... thinking that would work based on another thread I saw.