GTX surging and compression

[davidpriolo]

1997 gtx 787 my ski runs fine for about 10 minutes then starts surging from 6000 rpm down to 4000rpm back and forth. I have changed all the grey fuel lines ,all the filters , cleaned the rave valves, replace the fuel knob, and fuel sending unit($200+) readjusted the carbs ... I just did a compression test, the front cylinder get up to 155psi and the rear gets to 135psi is that a big difference and can that cause a surging problem??? Also one of the air vents under the rub rail fell into the hull cavity and is not set back in the gromet correctly is that a big issue? Any ideas would be helpful Thanks

 

[seadooya]

the pto cylinder compression is not good, considering the mag is 155, but it should run. Check the volts at battery, while holding 5500rpm, should be between 13.5-14.5v

 

[davidpriolo]

Thanks for the quick reply. I guess the PTO is the rear cyl correct? And yes the ski runs fine at idle in the driveway and good for about 10 minutes in the water then starts tehe surging or the rpms rise and fall and rise and fall

 

[davidpriolo]

could it be the Rectifier and if so whats a quick check? Also do you think a top end gasket change will help raise the rear cylinder comp.