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1996 GSX 787 - Wont rev past 2000 in water

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buffalojoe94

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I've been wrestling with this thing for a few weeks now and I can't figure out what's wrong.

Things I've done:
New top end
Rebuild the carbs
set pop off to 35 PSI
Set High and low to factory spec.
Checked to see if the rotary valve is in spec: it is

Out of water it revs right up no problem.
As soon as the back end it submerged it wont rev up, starts backfiring and stuttering when I give it gas, almost as if the exhaust is blocked. It will idle fine and I can putter around the lake but as soon as I give it more than 1/8 throttle the engine cuts out.

When I take it out of the water and start it, it will cough out all the water in the engine then rev right up. If I mess with it enough to get it moving in the water I can get some throttle response but if I stop it bogs down and stalls.
I tried to adjust the low speed and no change. Took the carbs apart again to make sure I didn't put them back together wrong, no change.

Anyone think it's not pumping water though the exhaust correctly?
 
Did you read the Troubleshooting Section?

I attached the Troubleshooting Section, but maybe you didn't bother to open it?

There's a whole Laundry List of Clues to follow...be proactive.
 
Oh yes. Indeed I did. Trouble shooting electrical, carb issues, fuel line obstructions and fuel line circuits. I did notice that on of the check valves in the hull was solid. I check the other ski and same issue. When the fuel runs out from the return line to the fuel take its suppose to vent off. I cut out one check and the other one kinda fell apart when I was trying to remove it from the hull. Lol. If the tank doesn't vent properly then it could cause fuel flow issues. I haven't tested it yet but once again it starts great on the trailer. Also when I checked the carb (second time) I noticed a small orifice restriction (brass) in one of the 4mm hoses from the carb to the accelerator pump. The short hose that supplies fuel to the diaphragm pump (accelerator pump)
 
In addition to the above, make sure it's not the rectifier. Symptoms were very similar to my 1996 GTX 787 with a failed rectifier.

Disconnect the red wire from the rectifier (and cover with electrical tape). Battery won't charge while it's disconnected, but if it runs great with the rectifier disconnected, you have the culprit.

 
Lothsahn said:
In addition to the above, make sure it's not the rectifier. Symptoms were very similar to my 1996 GTX 787 with a failed rectifier.

Disconnect the red wire from the rectifier (and cover with electrical tape). Battery won't charge while it's disconnected, but if it runs great with the rectifier disconnected, you have the culprit.

Click to expand...
Just dipped the ski in the water. I bypassed the fuel cut off switch, removed the fuel tank vent check valves. Still no success. While I had the machine running, I snipped the red wire from the rectifier and still no difference. Still same issue. Pump the throttle a little and pull the choke out a small bit and off you go right away. Full speed ahead but then let the choke go again and it bogs down to an idle.
 
Then either the Carbs are too lean or there's a massive Air Leak somewhere in your Engine causing a severe Lean Condition.

Do you have the Stock OEM Airbox or Flame Arrestors on the Engine?

Were the Rave Valves Rebuilt? Leaking Rave Valve System will cause a big Air Leak.
 
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Kinda throws me off a bit because it will start fine and rev fine when on the trailer but when the ski is dipped in the water (even on the trailer) it will bog out right away. It will then idle. If I have the ski floating and start it, ease up on the choke and then give it some throttle it will scoot on plane and hit top speed until I let off on the choke then it bogs right away back down to idle speed. Touch the throttle and it bogs... choke the carb.... off I go to top speed again.
 
This is a spare engine I have. This is not rave valve. My two skis have a single carb... the one in the pic (spare) has double carb
 

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LOL The Title says 1996 GSX 787 which is a RAVE Valve Engine.

If your Engine is different, maybe start another Thread? No hijacking please.

Hard to give good Troubleshooting Advice when you throw a Curve ball.

Remember, we are hundreds of miles away and we can't see your Engine nor are we Mind Readers.

Talk about getting cross-threaded...
 
Hopefully you didn't snip the red wire--you can just unplug it and plug it back in. In any case, it's not the rectifier.

You mentioned you rebuilt the carbs, and you put them back together twice. Dumb question, because it doesn't say so anywhere: Where'd you get the carb rebuild kits? Are they Genuini Mikuni?

If it's not Genuine Mikuni, it's trash. The carb rebuild kits on amazon, etc are worthless and will cause nothing but problems (and possibly blow up the engine with a lean condition if you run it too long).

Given pulling the choke fixes the problem, you're lean. You said you've bypassed literally everything (fuel selector, etc), so I'm going to list the things that you haven't checked or bypassed I know of:
  • Fuel lines - Does it still have the original grey oem fuel lines? If so, these need to be replaced right away. They dissolve from the inside out (especially with ethanol) and leave purple goo that clogs everything up. If the lines were old, you really need to recheck the carbs (especially the small filter in the carb) to make sure none of the gunk blocked any of the small passageways/filters/gaps
  • Water separator - Make sure it's clean and the strainer is in good condition. If not, replace with OEM parts if possible. The amazon strainers aren't as good.
  • Gaskets between Carbs and Block - If you have an air leak downstream of the carbs, it'll run lean. Make sure that there's no corrosion on the block where the carbs mount, that the gaskets are in good condition, and fully sealing.
  • Pop off spring - Did you keep the existing spring for the pop off when you rebuilt the carbs? Very often the springs that come in the rebuild kit aren't the right strength (and even if you set the right pop off, it won't run right)
  • Gaskets/o-rings where the cylinder head mounts - There's a large o-ring at the top of the piston. I'm not sure if this could be the cause because I think a leak here would pull water and not air, @mikidymac would know. Be careful if you do remove the head--there's a specific tension to make each bolt and they can strip so be sure to not overtorque (and use loctite as recommended)
Also, what model of Sea doo do you have? The 1996 GSX does have a 787, which isn't what you have. That engine likely takes different pop-off settings.
 
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Lothsahn said:
Hopefully you didn't snip the red wire--you can just unplug it and plug it back in. In any case, it's not the rectifier.

You mentioned you rebuilt the carbs, and you put them back together twice. Dumb question, because it doesn't say so anywhere: Where'd you get the carb rebuild kits? Are they Genuini Mikuni?

If it's not Genuine Mikuni, it's trash. The carb rebuild kits on amazon, etc are worthless and will cause nothing but problems (and possibly blow up the engine with a lean condition if you run it too long).

Given pulling the choke fixes the problem, you're lean. You said you've bypassed literally everything (fuel selector, etc), so I'm going to list the things that you haven't checked or bypassed I know of:
  • Fuel lines - Does it still have the original grey oem fuel lines? If so, these need to be replaced right away. They dissolve from the inside out (especially with ethanol) and leave purple goo that clogs everything up. If the lines were old, you really need to recheck the carbs (especially the small filter in the carb) to make sure none of the gunk blocked any of the small passageways/filters/gaps
  • Water separator - Make sure it's clean and the strainer is in good condition. If not, replace with OEM parts if possible. The amazon strainers aren't as good.
  • Gaskets between Carbs and Block - If you have an air leak downstream of the carbs, it'll run lean. Make sure that there's no corrosion on the block where the carbs mount, that the gaskets are in good condition, and fully sealing.
  • Pop off spring - Did you keep the existing spring for the pop off when you rebuilt the carbs? Very often the springs that come in the rebuild kit aren't the right strength (and even if you set the right pop off, it won't run right)
  • Gaskets/o-rings where the cylinder head mounts - There's a large o-ring at the top of the piston. I'm not sure if this could be the cause because I think a leak here would pull water and not air, @mikidymac would know. Be careful if you do remove the head--there's a specific tension to make each bolt and they can strip so be sure to not overtorque (and use loctite as recommended)
Also, what model of Sea doo do you have? The 1996 GSX does have a 787, which isn't what you have. That engine likely takes different pop-off settings.
Click to expand...
I sent you a message on a new thread
 
buffalojoe94 said:
I've been wrestling with this thing for a few weeks now and I can't figure out what's wrong.

Things I've done:
New top end
Rebuild the carbs
set pop off to 35 PSI
Set High and low to factory spec.
Checked to see if the rotary valve is in spec: it is

Out of water it revs right up no problem.
As soon as the back end it submerged it wont rev up, starts backfiring and stuttering when I give it gas, almost as if the exhaust is blocked. It will idle fine and I can putter around the lake but as soon as I give it more than 1/8 throttle the engine cuts out.

When I take it out of the water and start it, it will cough out all the water in the engine then rev right up. If I mess with it enough to get it moving in the water I can get some throttle response but if I stop it bogs down and stalls.
I tried to adjust the low speed and no change. Took the carbs apart again to make sure I didn't put them back together wrong, no change.

Anyone think it's not pumping water though the exhaust correctly?
Click to expand...
Did you ever figure this out as my 96 787 has the same issue?
 
mikidymac said:
Check the big rubber exhaust hose from the waterbox to the hull outlet. They can go bad from the inside and collapse causing your exact issues.
Click to expand...

I may of missed it but did you ever check this? I just had my third one over the years do this (one was on an x4 with a jetted pipe, might of let her get too hot ;)). I don't even put an OEM hose back in anymore, I do intercooler piping with silicone couplers and stainless t-bolt clamps on them all now.

They will free rev fine out of the water but when loaded in the water the collapse on themselves.
 
Mine did the same thing it was the file switch where you switch to reserve on and off I bye pass it just to check and it took right off
 
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