Question about top speed

[benjilafouine]

Hello,

Many of you will remember that I had to replace my engine and carb last year. The rotary valve was also a bit worn out but the dealer reused it. I did a few rides this so far and I am noticing this: my sea-doo GTI LE 2003 is going a bit less fast with the new engine. Otherwise, it runs perfectly.

With the old engine and old carb, I used to be able to go to 45 mph. With the new engine and new carb (currently set at factory specs), I can't seem to be able to go faster than 42 mph. Not a big deal but I am a bit curious why.

It seems that my ski reaches its total speed at 80% throttle. If I press down at 100%, the ski just won't go faster.

Is it because it is a rebuilt engine?

Thanks.

Benji.

 

[LouDoo]

Could be, some engine re-manufactures will actually lower the engine compression so the engine will last longer. You might want to check the compression.

Lou

 

[benjilafouine]

Actually I did after about 30 hours on new engine (now at 34 hours more or less): 145 on both cylinders (done by a professional just before winterizing it but top speed was the same last fall before winterizing). I also checked my speedometer running along with a friend on his own ski: dead on.

I just can't see why it would be slower as I didn't gain weight. :lol:

The only things I can think of are:

- engine running too rich (although the spark plugs are looking just perfect according to a friend who inspected them last week)?
- timing not perfect?
- carb not optimal?

I have to rule out the jet pump as nothing got sucked in (but got close due to a guy fishing at the end of the dock...). Otherwise this ski rocks. I rode about 3-4 hours so far this year and not a glitch.

Benji.

 

[Spimothy Leary]

Humidity, temperature?

Are these gps readings?

 

[benjilafouine]

Temperature was dry and 70 degrees when we tested it. I had my buddy riding on his ski just right next to me and confirmed that my speedometer was accurate (but not tested on GPS). Nonetheless, I know my old engine was at good 3 mph faster (on that same speedometer).

Benji.

 

[CReynoldsMIZ]

Temperature was dry and 70 degrees when we tested it. I had my buddy riding on his ski just right next to me and confirmed that my speedometer was accurate (but not tested on GPS). Nonetheless, I know my old engine was at good 3 mph faster (on that same speedometer).

Benji.

have you checked the wear ring and impeller?

 

[Spimothy Leary]

Temperature was dry and 70 degrees when we tested it. I had my buddy riding on his ski just right next to me and confirmed that my speedometer was accurate (but not tested on GPS). Nonetheless, I know my old engine was at good 3 mph faster (on that same speedometer).

Benji.

Ok, just curious, since there can be a large number of factors that impact top speed.

Compression
Temperature
Humidity
Weight (including fuel)
Water Conditions
Inaccurate speedo
Pump/impeller/ring condition
Jetting
Max RPM
Water Regulator
Fuel
Current or Headwind/tail wind.

I'm sure there are several more, i'm not much of a tuner, so there are probably fella's out there that can show a 3mph up/down based on minor tweeks.

Your RPM wasn't mentioned, so I bolded it, since that's a really big factor.

I know for a fact that my personal ski can record higher and lower speeds by 2-4 mph From Saturday to Sunday to any one or any combination of those factors, but usually for me its humidity/water conditions that impact these things.

I'm not the type that pays close attention to top speed/rpm unless something feels out of whack, then that's all I pay attn to so I at least have a baseline.

 

[benjilafouine]

No, I haven't. The whole pump was rebuilt 3 years back by the previous owner (because he had put some sand in it) and I had no incident myself whatsoever with it since I purchased the ski last year. As far as I know, this little difference in speed comes from the new engine or systems around it, but the pump. I noticed it last year as soon as the engine was replaced but I had some serious issues with the carb (someone rebuilt it and goofed up so I ordered and installed a new with factory adjustments). When I replaced the card end of September, I was hoping to get the speed back but I didn't so hence the question this spring.

The dealer at the time made two mistakes when he installed the new engine: didn't set the timing right (he had to redo it) and he screwed the carb rebuild until I got fed up and purchased a new carb).

Benji.

 

[benjilafouine]

To Spim, I don't have a RPM on the display; just speed and gas gauge. RPM sounds normal to me (but one hundred more or less, it is hard to ear).

I can rule out I believe:

Compression (145 on both cylinders)
Temperature (colder would be better, no? still very cold here, had some snow flakes this morning)
Humidity (not humid at all)
Water Conditions (water very very cold)
Inaccurate speedo (was confirmed with a friend)
Max RPM: cannot test
Fuel (super unleaded)
Current or Headwind/tail wind (no winds when we tested, lake like mirror)

What is left:

Weight (including fuel): need to try it on an empty tank
Pump/impeller/ring condition: I doubt there are issues there but I cannot rule out completely
Jetting: same as above
Water Regulator: what is that???

Really, there is a clear cut between old and new engine/carb. Maybe other members here can tell me what they achieve with their GTI LE.

Benji.

 

[Spimothy Leary]

I thought 717's ran on 87 octane... not super....
(sorry I've never owned a 717 except to sell it)

was your old carb jetted and adjusters set exactly the same as the new one?
(perhaps 717 guys can chime in on tweaking adjusters)

RPM, is not a feeling, IMO there is absolutely no way to tell if your down 100 rpm's unless your Jammin Jeff or somebody special, if you really wanna dig into this now or down the line, pick up a tto tach, at least then you will have specifics.

lastly, FWIW, and I think others can confirm this, some engines just run a tad faster than others even when there is no real logical explanation, they just do.

Water regulator is the black thing on top of the waterbox with a red dial on it.

my guess (emphasis on guess) is that your rpm's are down slightly, which would explain pretty much everything except why rpm's are down.

no water in the hull?

 

[benjilafouine]

Nope. No water. No leaks at all. Stays in water for days sometimes (but I check it every day). I have this old habit of using 91 octane in all my gasoline stuff.

As for the carb adjustement, and for those who now my adventures of last year, dealer screwed my carb solid so I have absolutely no clue how it was set before. So when I installed the new one, I left it at factory settings. That could be adjusted I guess.

This ski runs fine, but as you said, maybe it is just the way this engine was rebuilt. Aside from the carb or the timing not being dead on (although I have no reason to believe that it is not, short of opening the cover), I cannot see anything else.

Benji.

 

[WhiskeyD]

If it's been 3 years since the wear ring was replaced, there's a good chance it's got some wear and causing a loss of speed. I generally replace mine about twice a year. But I beat on my ski hard

 

[1983]

WHen you replaced the carb, and put the throttle cable back on. Did you verify the throttle plates ( butterflies ) are opening 100% ( WOT wide open throttle ) ??

If they arent, there is your culprit.

Also as mentioned above, pull the black cap off the WR ( water regulator ) its a simple spring clip, then pull the diaphragm assembly out and inspect for a rusty spring clamp that has pierced the diaphragm. That was the culprit on one of my skis to loss of top speed RPMs.




Rob

 

[benjilafouine]

Rob, I had given a thought about the throttle cable. Maybe I should check that indeed. Question: when I hit the throttle, I get max speed at 80% throttle. If I go to WOT, speed stays the same.

Here is why I thought about that (last year): what happened last year is that I purchased the new carb online (from OSD parts) but had the dealer install it to prove my point (that they had screwed the old carb). I also know for a fact that they had played with the throttle adjustment when the old "rebuilt" carb was not working well (before they put the new one in). So it is possible that the throttle cable is not 100% correctly adjusted given the fact that they screwed several times during that rebuild...

I am not mechanically skilled but I guess I can check that by opening the carb cover with a friend over the weekend (he is pretty good at it). Any advice?

As for the water regulator, what does it do exactly?

And [MENTION=33499]WhiskeyD[/MENTION], for the wear ring, my ski is due for an oil change in the jet soon. Maybe I should check it at the same time. But all in all, the ring is certainly not older than 100 hours (and not beaten). Is that old?

Benji.

 

[Matt Braley]

A lot of good possibilities have been mentioned here. I'd like to add alignment as another potential culprit. If they did not get the drive shaft straight the side tension can cause drag that robs rpm.

 

[benjilafouine]

Matt, if the shaft wasn't align properly, wouldn't I experience more severe issues like cavitation or some vibration or noise? Obviously, 3 mph is not a lot. Guess at that point it is fine tuning (for which I am null!). Bring me a broken computer instead!

Gee, can't wait to retire and have all the time in the world (like James Bond). I am leaning towards it... One more year and it's half retirement!

Benji.

 

[1983]

If it wasn't gps to gps comparison then I wouldn't be concerned there is no accurate starting point to compare to.

Also if you aren't in the exact identical nozzle trim position as last year then you can lose top end speed.


Rob

 

[benjilafouine]

Nozzle trim???

Benji.

 

[1983]

Does your ski have adjustable trim?

 

[1983]

I only mess with older 2 seaters, looks like your ski doesn't have adjustable trim.

Check the WR as mentioned earlier, and GPS comparison is really what matters.

 

[benjilafouine]

No. Not at all (maybe manual but a mechanics told me no).

GTI LE is a very basic ski. Some didn't even have a speedometer. Mine does. It is a barebone ski.

Throttle cable is my best bet so far. Them impelling wear ring.

Benji.

 

[1983]

Check throttle butterflies as I mentioned earlier. But without a before accurate GPS mph reading there is nothing to compare to. Ride the ski and enjoy it.


Rob

 

[benjilafouine]

Otherwise this ski rocks!!!

 

[benjilafouine]

Also, oil in the jet pump is two years old. Must I replace it? This would be a good time to inspect it. Is this hard to change?

Benji.

 

[XP 787]

Also, oil in the jet pump is two years old. Must I replace it? This would be a good time to inspect it. Is this hard to change?

Benji.

It is fairly simple to change. Pull the nozzle, then remove 3 allen screws from nose cone. As oil is draining make sure its not milky, this indicates water getting in there.