1999 750 SXi Pro w Factory Pipe - Engine dies while riding but restarts immediately

[NorthSki]

Hey guys,
I bought a 1999 750 SXi Pro last fall and have been working some of the kinks out of it. It's pretty clean but does not seem to have been used for some years. It has the big Factory Pipe set up on it. I am familiar with 550s and 650s as I have a few but always wanted an SXI Pro.
It fires up and idols perfectly. It's power on take off is good but not what I remember when I had a stock one many years ago in the mid-90s. While riding it sometimes just dies. No sputter or surging, it just stops like someone hit the stop button. It restarts immediately, sometimes with a bit of bog getting out of the hole but then rides well. It appears that when someone rides it very slowly it does not die. When I jump on it does. I think this is a fuel delivery issue maybe but as I look at it more I realize I am not sure. I was hoping you all might know where I should look next. In line fuel filter appears clean. It's one of the clear ones from Hot Products.
Thanks!

[JC-SuperJet]

1st Take Cylinder Compression Readings and report back.

If Compression is within acceptable range, then the Engine is probably having LEAN seizures, Could be due to Air Leaks (old Crank Seals), failing Carbs, clogged Fuel Tank Pick-Up Screens, clogged Internal Carb Filter, leaking Exhaust. not enough Cooling Water etc...

[NorthSki]

Thank you JC-SuperJet. Will get new compression test this weekend. Appreciate the help.

[wmazz]

It fires up and idols perfectly. It's power on take off is good but not what I remember when I had a stock
one many years ago in the mid-90s.

The SXi Pro has special needs.It has the most exhaust port timing of any of
the SX jet ski's. So it can be a little soft out of the hole, but it doesn't have to
be that way. Because the porting is near a PJS stg 5 port specs, the peak rpm
of the engine needs to produce is very high to prevent detonation.

While riding it sometimes just dies. No sputter or surging, it just stops like someone hit the stop button.

It restarts immediately, sometimes with a bit of bog getting out of the hole but then rides well.

A WOT seizure is a common problem among all watercraft when the performance
parts are not matched, or when a group of problems combine to cause the seizure.

Restarting immediately and still has good power is another sign of a light seizure.

People often rationalize the problem and assume it ran out of gas or something.
Because of this people continue to ride their ski's. As you know it continues to
seize at wot, and after 10 or more light seizures, preignition occurs and causes
a major seizure that is obviously a big deal.

It appears that when someone rides it very slowly it does not die. When I jump on it does.

I think this is a fuel delivery issue maybe but as I look at it more I realize I am not sure.

Back in the late 80's we had many wot seizures on the 650 SX & X2. There was
a theory that the fuel pump output decreased with rpm and a larger needle and
seat was required prevent a lean seizure at wot.

But the problem (that looked like a lean seizure) was actually the impeller.
(There were other poorly designed product like the Ocean Pro head that
also contributed to many wot seizures).

There is a good possibility that your initial results of a compression test
may look good. An engine with a light seizure may have normal compression.

But if the compression test is more than a few psi difference
between cylinders, that is not normal.

Be prepared to remove the cylinder head (you can reuse the gasket) and
take some pictures.


Bill M.