• This site contains eBay affiliate links for which Sea-Doo Forum may be compensated.

99 GS 717 Acceleration and WOT problems

Status
Not open for further replies.
S

seadooxps

New Member
The ski is actually a 93 xp. It has a 99 GS 717 engine with a single 40mm mikuni (all stock 99 engine and carb).

It will accelerate to around 3500-4500 rpm usually with no problem (just barely planed off). At this point it will sometimes bog for either minutes or a few seconds and then "roll" onto WOT. While its barely planed off, if i can get it to cavitate (by either hitting a few waves or leaning hard to the side), it will take off to WOT perfectly every time. At first we thought it was loading up because of a problem with the oil pump (decided to use a block off kit and premix). Then we thought it was a carb issue so its has been completely rebuilt. We also changed all fuel lines. There are quite a few things that I have already tried in order to fix this problem.

1) Compression 135 Mag, 132 PTO
2) Complete carb rebuild with OEM Mikuni kit including internal filter and all fuel pump diaphragms
3) All new gas lines
4) Converted to Premix with WSM block off plate
5) New inline filter
6) Checked water separator
7) Checked fuel pickup
8) New intake manifold o-ring and carb to intake gasket
9) New plugs a few times (plug chop shows correct burn; a light tan/brown)

Rarely it will work perfect. Usually from the get go it will mess up though, taking a quite a few seconds to plane out. Like mentioned before it can even take minutes. Any good advice will be appreciated. I would love to get this fixed. My two xp's have been nightmares and I need to restore my faith in Seadoo's!!!
 
Last edited by a moderator:
Quick question...when you upgraded the engine did you upgrade the MPEM,(Multi Purpose Electronic Module)? If you using the old mpem, that could be you problem.

Karl
 
The ski will accelerate normally every time if i can get it to cavitate while it is bogging down around the 4000 rpm like mentioned before. Unless it cavitates to allow the engine to spin up it is very difficult to achieve WOT. Once it does cavitate and catch, it takes off like its supposed to.

Thank you!!
 
That is exactly what my sKi is doing. I have a 2001 gts with a SBT 717 re-engine, single carb, good compression.

It will not accerate (increase RPMs) after 1/2 throttle, full throttle or 1/2 throttle same RPM. If I keep it at WOT and hit a series of waves, boat wakes, the pump will come out of the water and the engine will rev up and when it lands back in the water it will take off like a bandit. If I keep it at WOT, it will keep the RPMs up and fly. If I let off the throttle, its back to the same condition, WOT or 1/2 throttle, same speed/RPMs.

Kustomkarl , you mentioned MPEM,(Multi Purpose Electronic Module)? On a re-engine, could the MPEM be the culprit? I have been try to fugure this for over a year. Carb has been rebuilt, two repair shops have not been able to figure it out. I always had the suspision it could be an electrical issue.
\
I think you may be on too something for both of us! Where can we buy an MPEM, what year or type of one would we buy to match our upgraded engines?
 
Research...

This is unusual. I'd like to look into this more, so if there is any more information you can gather, I'd like to hear it.

Why you can get to 4k rpm, bog, then hit a wave to allow the impeller to freewheel and go max rpm in air, then land and maintain rpm, is really strange. The idea that you can't make that torque would point toward the compression but that would mean, you'd never get to WOT. So, I find this strange and will see what I can come up with.

We, nomally don't work with mods of this type, since you have to change out almost everything for this to work. It appears SeadooXPS already knew this because the 93 XP with the 657cc engine wasn't equipped with an MPEM. It had the simple "electronic" module, so I'm sure he had to revamp the entire electrical system to even get it to a working stage.

K-Jack, your problem, although similar, I think may be from different causes. I'll be back to this thread when I can find some type of conclusion as to why this may be taking place.
 
Everything that k-jack says is exactly what I was trying to convey. It will not achieve WOT unless it has a chance to freespin, even if it is only for a second or few seconds.

I have tried everything that I can come up with and have spent over 20 hours researching online about this one issue. However I have probably spent over 25 hours on the ski! I have a very similar ski, a 95 xp with the 717 but it has twin carb (same hulls, same weight, etc.), and when both are wide open, they have the same amount of power and speed. Also both ski's have the same compression (within 2-3 lbs).

I appreciate the advice! Hope we can sort this out.

p.s. seadoolover I am purposefully trying to get the ski to cavitate while its barely holding plane, otherwise it won't reach WOT. Cavitation isn't the problem, so far it's the solution! lol
 
Also, this engine is a brand new OEM engine that was a leftover straight from the factory and was shelfed for the past 8 years. Everything is brand new on it. I often considered it being an electrical issue, but it seems directly related to fuel because it can achieve WOT and just like k-jack's, if it comes off plane (i stop for any reason) it acts exactly the same way. It will just stay right at the 4kish range until i get a chance to get the pump out of the water, then WHAM she's wide open and won't back off until I tell her. I have even run it for miles and no problem until I chose to let off. I would also like to mention it sounds great, it seems strong, and rarely it will slowly climb to WOT. Also I found it kind of odd that the fuel outlet hose to the tank from the carb (not the pulse or "in") seems to have alot of pressure. I did also change these lines, tested the check valves and made sure there was no blockage. The carbs have also been taken apart numerous times and checked and rechecked. The intake manifold o-rings are fine. The exhaust system seems fine (have not had it completely off). The only other thing I could think of is that one time the muffler to waterbox hose slipped off and it wouldnt plane but I tightened the waterbox hose and it was fine again (a couple months ago).
 
I will add one more curve ball into the game. Last year, off the trailer the ski would achieve WOT no problem, after i ran it for several minutes and it was warmed up, back to the same issue, I would then try to run down a boat wake to catch some air and get the engine to (cavitate/rev up) to get the RPMs up. This year off the trailer, it the same thing hot or cold. The ski cruises ok, but, 1/2 thrttle to full throtttle no difference in RPM unless I hit a boat wake.

Compression is good (145) both skis, we have two of them, this one I cant figure out...

Appreciate the wisdom you all have, cause mine is stymied..
 
Grease fittings....

Have you checked and/or serviced the grease fittings on the shaft at the PTO hub and at the "thru hull" fitting?

Torque and compression don't seem to be an issue.

Have you tried to increase your fuel mixture? If not, I'd mark your mixture screw, then, open a quarter turn. What do you have to lose?

Without being there, I'm kinda stuck on this one.

Seadooxps,....have you checked the tank vent line. When you feel this return line you say feels like its under pressure, can you loosen your fuel cap to see if there is any pressure behind it?
 
Last edited by a moderator:
Yes there was pressure behind the vent line so I even disconnected it for a short period of time just to see if it would help and it didn't. I replaced every fuel line including every vent line as well. If the carb vent were to be clogged what symptoms would occur? By the way The PTO has been greased properly and the pump seems to be in good shape (I had it off a few weeks ago). If there is anything I could be overlooking I would be HAPPY to check into it! I have checked everything at least twice, but I can check it again! Thank you for your time guys. My carb is the mikuni 40mm single (420 model number) which suggests that the low speed is open 1 1/2 turns and the high speed at 0 (zero). Just to be safe I opened the high speed up to 1/2 turn and no difference. The plugs seemed to be burning properly at the zero setting. I would like to add that the problem did progress, meaning it would run great for shorter and shorter periods of time and then have this symptom. Now it has this symptom no matter what. The longest I ever had it working properly would probably be an hour and a half.
 
I will check into the lubrication of the PTO and thru hull fitting.

HAd the ski out and seat off, adjusting the carb, no change.

Is there anything else that can limit the torque? Reasons being I have to get the ski out of the water to reach WOT RPM. Could it be a timing issue? It doesnt seem like its an electronic issue. Im stumped too. Thansk for your thoughts, I will get on this lubrication concept!
 
k-jack, seadooxps....WHAT'S UP.....i'm hav'n the same problem w/ 96' sportster. Get past bouys, WHAM, WOT til i run out of gas, roll the throttle off abit, then motor wont turn past 3-4k. I mentioned in another thread, that, i replaced everything, wires, cables, coils, p[lugs..etc, NUTHIN.
My rebuild kit for carbs comes in tomorrow with dif'nt rate float sprng and 2.0N/S. I'll post if made/not made progress.
 
I had a similar problem with one of my Kawasaki standup competition Jetskis. It had me going for a couple days of testing...it wound up being the pop off pressure in the carb was off. The pop off pressure is a way to determine the correct needle valve size and Arm Spring combinations. A table chart is used for the correct calculations, based on pop off pressure. Too low a pop off pressure, the richer the mixture is at low end. You need to adjust the spring arm to allow pop off at the correct amount of PSI, based on the Needle valve size and Arm Spring size. it's worth a look at.

Karl
 
Yes!!!!!!

J/K....just got back from lake. have 96' sportster, was told, shud have 36-60 psi pop off, w/ 1.2n/s, this wasnt work'n. So changed to 65gm spring, which is high/low 40/50psi. In lake, same crap, so installed 2.0n/s w/ 115gm, turned LSA 1out, same crap, did plug check, whitish,brown( to me, in between lean,good), so adjusted HSA to half/3qtr out. Same DAMN thing, BUT..., when i hit my own waves, BAM, boat took off, she will stay running tili run out of gas. So, i'm think'n when i reassembled the motor, i believe set it to the case markings, (dumb thing) think my boat calls for 159degree marking.
So i said the heck w/ it for last couple hrs and grabbed the fish'n poles.
Next step is to set valve at 159degree and put 1.2n/s back in, not dificult to swap out in parking lot, and see if any progress....Tim
 
Scratch last paragraph

From reading numerous post, to me, the rotary valve itself comes in 130,147,159 degrees, and that you set at the 130* markings, and 65* marking. If this is right/wrong, might of got ahead of myself....Thanks
But, as far as previous post to this thread, hop'n somebody figures it out
 
Partial clerical...

Just read from previous post about (720/800) timing, that they use 159* valve, with 147* opening....
So, gonna set mine, post something when finished
 
SOunds great leep us posted. There may be something to the engine replacement that is causing this. When the new engine was installed they may not have set the rotary valve correctly. thx
 
i am having a very similar problem as you guys. wish someone could figure this out lol, i also have perfect 140 comp on both one plugl (top towards front of ski) is rich though other is nice and chocolaty.
 
"it wound up being the pop off pressure in the carb was off"


I think I'd check this first. (As Karl said)

If that fails, you could add some sort of line to the plug in the top of the flame arrester, so you could add a little additional fuel, and at least determine if it is a fuel shortage problem. Maybe just a can of spray silicone, to dose it with.

And, I sort of think I'd try this with the seat off. You know, you could cause an explosion inside, if the seat was on it.

Just for a short test run. This way you could determine if it is a fuel problem.

But, by elimination, that could help you diagnose the problem.

Best I can do fer ya. (of course you could take it to a pentecostal preacher, But I cannot vouch for this method!)

Nate
 
If you pull out the choke when you cant get above the 3-4000 RPM does it make any difference? Does it help or seem to seem to make it worse?

Ryan
 
Status
Not open for further replies.

Similar threads

Legacy37
97 gti stumbles off idle, feather the throttle runs great
Replies
4
Views
204
Legacy37
Legacy37
Kra_880
'99 GSX LTD snapped return fitting
Replies
1
Views
125
Kra_880
Kra_880
W
Help with 717 single carb
Replies
9
Views
525
wmshay6
W
G
717 carb leaking/dripping from venturi
Replies
6
Views
260
Venturian1
V
1
1995 Seadoo Gtx Fuel System Questions
2
Replies
26
Views
872
burtshaver2021
burtshaver2021
Back
Top