Porpoising cured on 99 GSX-L

[Highmaster2]

Had a real problem with porpoising on my 99 GSX-L. Even with my 275 lb. butt on it, the trim all the way down and a full tank of gas, it would still porpoise uncontrollably below 40 mph. It was uncomfortable to ride in any level of chop - just wouldn't stay in the water - porpoising constantly. I had already adjusted the VTS rod as long as it would go. If you went WOT from idle, it would jump straight up and just bounce across the water (that's with the VTS all the way down).

I found a threaded sleeve that was 3 inches long. I cut the VTS rod in half. I threaded the two halves to fit the threaded sleeve so that the overall rod length was 1" longer than original. This allowed the VTS to trim lower than normal but still not run out of room.

Now, with the VTS indicator at the mid position, the GSX-L stays stable at most any speed - no porpoising. If the chop gets worse, I can trim down a click or two and the GSX-L stays smooth. Trimmed all the way up, it still trims up enough to run the fastest it has ever run (63 mph on GPS and not even on glass)

Anyway, the fix works for me - It has now become almost as "rideable" as my 2001 GTX 3-seater. Maybe some others can get some benefit from the info.

 

[SabrToothSqrl]

I also disliked how much the GSX would hop.... Extending the VTS rod seems legit.

On boats you usually add trim tabs as well.

 

[Seadoobuddy]

Had a real problem with porpoising on my 99 GSX-L. Even with my 275 lb. butt on it, the trim all the way down and a full tank of gas, it would still porpoise uncontrollably below 40 mph. It was uncomfortable to ride in any level of chop - just wouldn't stay in the water - porpoising constantly. I had already adjusted the VTS rod as long as it would go. If you went WOT from idle, it would jump straight up and just bounce across the water (that's with the VTS all the way down).

I found a threaded sleeve that was 3 inches long. I cut the VTS rod in half. I threaded the two halves to fit the threaded sleeve so that the overall rod length was 1" longer than original. This allowed the VTS to trim lower than normal but still not run out of room.

Now, with the VTS indicator at the mid position, the GSX-L stays stable at most any speed - no porpoising. If the chop gets worse, I can trim down a click or two and the GSX-L stays smooth. Trimmed all the way up, it still trims up enough to run the fastest it has ever run (63 mph on GPS and not even on glass)

Anyway, the fix works for me - It has now become almost as "rideable" as my 2001 GTX 3-seater. Maybe some others can get some benefit from the info.

I have the same ski but haven't ridden it enough to notice. What is a threaded sleeve?
Can you post a few photo of the fix?

 

[Highmaster2]

Failed to take a pic before I installed it. A threaded sleeve - imagine a hex nut. Now imagine the hex nut to be 3 inches long and the trim rod, after being threaded to fit the sleeve, screwed into the sleeve 1 inch on each end. I do not remember what size threads the sleeve had. I measured the rod diameter, decided the largest size I could thread it for and ordered a stainless sleeve to fit. I can't even remember where I got the sleeve, unfortunately, as I bought it several months ago and modified the trim rod. I finally remembered that I had done so :facepalm: and decided to install it. Sorry I can't provide more specific info, but hopefully this will provide a starting point if someone wants to try it.

 

[SabrToothSqrl]

You could also make your own, longer VTS rod. Keep in mind the reason for the weak plastic 90 on the rod is so it's a sacrificial part. Better to break a $8.00 rod than a $200 VTS.

 

[Seadoobuddy]

I assume you are talking about the rod Part #1 in the diagram and the right angle is the end towards part #39.

http://partsfinder.onlinemicrofiche...seadoopwc&a=271&b=19&c=0&d=-PROPULSION-SYSTEM

 

[Highmaster2]

Seadoobuddy - Correct. That is the part that I lengthened by 1".

SavrToothSqrl - is that rod just threaded into the plastic 90? If so, that would definitely make it easier to do what I did. Just thread a longer piece of rod.

Was out on it today in enough wind to cause white caps. Previously I would not have considered taking it out when it's that rough - it just beat me to death. Now I am able to trim down enough the stop the porpoising and to let it plane on top of the waves at whatever speed I was going. It's like a totally different Doo.

 

[Spimothy Leary]

interesting idea, i've only been on the gsxL for tops a few hours, mostly in river conditions, light chop, nothing over 12". My experience did not indicate a tendency to porpoise, at least nothing noticeable, especially compared to my 96xp . but hey... if it works for you, it might work for somebody else too !

 

[Sportster-2001-951C-Stock]

Purposing is generally a result of having too much rocker in the keel.

My Sportster being both short and having rocker tends to purpose as well, I noticed the nozzle lower pivot is adjustable to two separate locations so I swapped it to point the nozzle to the high position and this helped to reduce the purposing by about 1/2

 

[SabrToothSqrl]

Alternatively you could drill a hole lower on the top of the nozzle which should give you more throw up/down

 

[scrisp]

Is the VTS cable/rod adjustable on the stock system? I looked through the manual and saw nothing about VTS adjustment or specs on what range the nozzle should move. On my 96 XP, I swear the VTS in the down position rides about like my SPX in the up position. It porpoises really bad. I took it out today and even on really smooth water, it beats me to death, no matter whether it's up or down. I am thinking that maybe the previous owner messed with it.

I may end up going with the idea that Highmaster came up with, that sounds like a very easy fix for the problem.

 

[SabrToothSqrl]

I think it should move up/down 5 degrees but
Don't quote me.

 

[scrisp]

I shot a video of it last night and it definitely tilts way more upward, then down. It barely goes past level when pointing down, but is probably about 15 degrees upward. I need to get outside and look closer it the system and see if it adjusts at all. Weird that it is nowhere in the shop manual.