98 Sportster 1800 - Is elevation my problem?

[coachjjohn]

I have been reading a bunch of different threads on this issue and understand that the issues could be: cavitation/wear ring/carbon ring/impeller angle/etc. Let me lay out my situation and I would appreciate your ideas/insight:

I live at 5800 feet elevation in Wyoming. The lakes we usually frequent are anywhere from 5200 - 6800 feet elevation. I know this affects my horsepower. My top speed is fine (mid-40's) with the RPM's at about 6500. The boat accelerates decently when not towing anything - it doesn't shoot right out of the water, but planes pretty quickly. I feel no vibration at all whether cruising or towing.

Based on what I have learned from you guys, here is what I have done:

A) WEAR RINGS: Removed both jets to look at the wear rings. One is nearly flawless. (I think the previous owner had it replaced within the last 2 years). The other has some scratch marks, but not uniformly all the way around (perhaps a bent shaft?) Overall, I don't think it's terrible.

B) IMPELLERS: both have some small nicks here and there, but not big chunks missing or obvious bent spots. I haven't fully removed them (don't have the tool yet). They do look like they have possibly been smoothed with a grinder at some point. I have no idea how to tell what angle they are. I did get a long number off of them that could probably give me that info.

C) I haven't checked the carbon rings - am just learning about that.

D) FINS/STATORS - several fins in both housings have chunks missing. How big of an issue could this be? I can't find much info on the effect could have? And if that is the likely culprit, do I replace the whole pump housing?

So - where do I start?
? Elevation/HP/Impeller angles?
? Wear rings/Carbon rings
? Fins/Stators (is there a different name for those?) in the housing?
? Put it all back together and be content to pull my 14 year old on waterskis and tell my 230 lb son to take a big breath and hope for the best?

Sorry if you feel this stuff has all been discussed - I just couldn't find much about the effect elevation might have.

Thanks for any info!

 

[2x2smoke]

It sounds like you think the motors are running properly but Did the boat come from sea level? Is it jetted for your altitude?

Are the motors bogging or singing when you go full throttle? If the motors rev and the boat doesnt go anywhere, thats cavitation. If they bog then its a motor problem or maybe the pitch issue you wonder about.

It wouldnt hurt to swap out the housings with the missing chunks, regardless.

 

[coachjjohn]

The motors run great - I think it has been jetted for our altitude from the previous owner. The motors don't bog when I tow something - Just takes forever to get up to speed. I did get a response from one of the parts places that sells impellers and he said the highest he has heard of them dealing with was 3000 feet. I know a lot of my friends with I/O boats have purchased what they call "High-elevation props", so I will probably continue to look that way.

BTW - since my original post, I removed both Jet pumps and took them all apart, replaced gear oil, re-assembled, etc. It's definitely not a wear ring issue. The impellers are stock Sea-doo impellers. The numbers I found on them led me to a chart that says the pitch is "11-22". I don't know what that means. Any help there?

2x2smoke - thanks for the response. I'll add more info if I find out anything else.

Have a great day!

 

[2x2smoke]

ok I think i understand your question a little better. You are wondering if the stock seadoo impellers cavitate at higher elevations even if they are in good condition. Like water boiling at a lower temp at altitude.

 

[coachjjohn]

The missing fins under load could be your problem...altitude should not be a problem..,,its hard to see from your pics,,,a small 2 seater can get away with pieces missing,,,but a large jetboat mass,,,I doubt it.

Sorry - wish I could've gotten better pics of the vanes. My impeller removal took is in route, so when I can get the impellers off, I'll get better pictures and post them.

At WOT, I am getting about 6200 RPM. I think it should be closer to 6800. That's why I am wondering about the altitude/prop angle/loss of HP issue. Thanks for your help.

 

[mikidymac]

We run up to the Sierras from sea level to the lake that is at 5,600' at least once a year.
I have never messed with our carbs and they run fine for these trips. I can tell you there is a huge reduction in power and top speed just due to altitude. The first time I couldn't believe how much of a difference there was but now I have come to expect it.
My 2001XP with the 951 will hit 60 mph all day long at sea level but at 5'600' it struggles to hit low 50's.
Your issue is elevation.