1996 SeaDoo GTX 787 Can't Hit High Revs on Water

[vgeraci01]

First timer, great stuff here! Read some threads like this issue, just can't find an exact one.

On trailer with hose hooked up, ski hits the rev limiter no problem - instant reaction to throttle, idles fine around 3100, on water idles around 1300. The problem is when it's on the water - can't get over 4000 RPM, gets there fast but bogs down right at 4000. Holding throttle at full it feels like it's just not getting enough fuel (chugs) but on the hose it's fine. Is it the load on the impeller and the demand for more fuel causing this? If so, how do I get more fuel through (and is it that easy)?

Here's what I have done so far without any positive results:

New fuel and oil filters
Removed and cleaned rave valves - new caps and springs
Drained gas and oil, using XPS SeaDoo/SkiDoo oil (it's red)
Removed and cleaned carbs (did not rebuild)

No oil or fuel leaks, hull clean.

That's it so far, I am not very close to a body of water to test on, so when I am I want to have all the necessary parts to replace and tune.

Thanks.

 

[mikidymac]

1. What fuel filter did you replace?
2. "Cleaning" the carbs never works, ever. Rebuild with all new Genuine Mikuni Parts.
3. Replace fuel selector.

 

[burtshaver2021]

Could also have a look at the rave valves,

 

[vgeraci01]

Could also have a look at the rave valves,

Rave valves were pretty charred up, took some sandpaper after the cleaner to get them fully clean. Anything else I should've inspected with those out?

 

[vgeraci01]

1. What fuel filter did you replace?
2. "Cleaning" the carbs never works, ever. Rebuild with all new Genuine Mikuni Parts.
3. Replace fuel selector.

I'll have to go back in there to see. I'm figuring there are more than one with your reply. Probably off the reserve?

 

[burtshaver2021]

Rave valves were pretty charred up, took some sandpaper after the cleaner to get them fully clean. Anything else I should've inspected with those out?

The o-rings and the bellows for any holes

 

[burtshaver2021]

Rave valves were pretty charred up, took some sandpaper after the cleaner to get them fully clean. Anything else I should've inspected with those out?

Oh and some of the rave housings have a little tiny hole through them, check that it’s clean if it has one

 

[vgeraci01]

Ok, rebuilt the carbs with OEM parts, replaced all fuel lines and the 2 thin oil lines from the pump to the cylinders, swapped the other oil lines out a couple years ago. Let it crank until the oil made it to the cylinders. Fired up with a little starter fluid, ran about 3 minutes on hose, and I think I blew the head gasket. Water started streaming out in a very thin stream between the crankcase and the cylinder on the back carburetor side. I wish I was videoing so I could post but shut it down immediately.

Anyone ever changed a 787 head gasket? Have done plenty lawnmower gaskets. Does it require additional gaskets to be replaced because of dismantling half the motor? I can't find any specific videos of the process online.

Thanks.

 

[mikidymac]

Did you use really high water pressure?

You don’t need much to keep them cool. Also more than a minute and you can burn up the driveshaft seal out of the water.

If you have water leaking out of the seam between the cylinder and crankcase you blew the base gasket not the head o-rings.

You better run it without water and make sure you didn’t force water into the crankcase.

 

[vgeraci01]

Did you use really high water pressure?

You don’t need much to keep them cool. Also more than a minute and you can burn up the driveshaft seal out of the water.

If you have water leaking out of the seam between the cylinder and crankcase you blew the base gasket not the head o-rings.

You better run it without water and make sure you didn’t force water into the crankcase.

I just used my hose, like I always do. Base gasket, is that the bad one (more work), looks like it. I ran the water out for about 20 seconds after I took the hose off.

Any advice for replacing the base gasket?

 

[mikidymac]

Make sure you get the same one that is in it as they are different thicknesses and identified by the number of holes punched in them.