Sea Doo 787 Loss Of Power

[froggystyle14]

Hello I have just purchased a 1997 Sea Doo Challenger 1800 with dual Rotax 787 motors. One of the cylinders on the port motor was cracked on the outside from inproper witerization I suspect. The motor has been bored .50 over so I had the new cylinder bored with .002 clearance. I used the same piston and rings. After putting back together I put boat in the water and let motor warm up properly then tried to add power the motor ran fine up to 5000 rpm then I went to 6000 rpms and the motr ran for about 5 seconds then shut down. I refired the motor with the same results over 5000 rpms. If you catch the motor soon as it starts to stall and idle it back it will stay running or if you pump the throttle it will stay at about 4500 rpms because the accel pump is pumping fuel. I tried switching the carbs from starboard motor and the same results. The motor has 160 psi comp. The carb gaskets I got in the rebuild kit are thinner compared to the ones that came off it. I cleaned the rave valves and they seem to move freely. Sorry for being long winded I am just trying to explain everything because I am out of ideas. Please help

 

[Nate Surveyor]

It sounds fuel starved.

Nate

 

[froggystyle14]

Hello I have just purchased a 1997 Sea Doo Challenger 1800 with dual Rotax 787 motors. One of the cylinders on the port motor was cracked on the outside from inproper witerization I suspect. The motor has been bored .50 over so I had the new cylinder bored with .002 clearance. I used the same piston and rings. After putting back together I put boat in the water and let motor warm up properly then tried to add power the motor ran fine up to 5000 rpm then I went to 6000 rpms and the motr ran for about 5 seconds then shut down. I refired the motor with the same results over 5000 rpms. If you catch the motor soon as it starts to stall and idle it back it will stay running or if you pump the throttle it will stay at about 4500 rpms because the accel pump is pumping fuel. I tried switching the carbs from starboard motor and the same results. The motor has 160 psi comp. The carb gaskets I got in the rebuild kit are thinner compared to the ones that came off it. I cleaned the rave valves and they seem to move freely. Sorry for being long winded I am just trying to explain everything because I am out of ideas. Please help

I also tried switching the fuel lines from one motor to the other and the starboard ran fine with the port fuel supply but the port one did not. I am sure it is fuel starved but I do not know why.

 

[Nate Surveyor]

A little list, (This may not be it, but it is practical, and as you go down, becomes more complex)

Gray fuel hoses. (Search gray fuel lines)
clogged fuel select valve. (disassemble, and clean out)
leaking pulse line from crankcase, which works the fuel pump. (Replace little hose, and check the fittings)
clogged filter inline, (water trap)
plugged vent hose.
pinhole, in gas feed line
little filter inside carburetors.
bad pop off pressure, in carbs
Sticking diaphragm
Sticking fuel inlet valve
Loose Carb, allowing direct air into engine, or bad gasket on carb/manifold, allowing air in.

This is not a comprehensive list, and Timmy may chime in with the rectifier wire thing, but I don't know enough to help alot more.

Hope you get her going!

Nate

 

[Gunsrunner]

Sound like carbies and fuel supply are out.
I would check charging, bad stator can also stop a motor around 4500-5000rpm.
Otherwise i would check pulse line as said before.