This has been driving me nuts. I have a Seadoo GTI Le RFI 787 with a 9 tooth SBT Starter that is 4 months old.
The starter will crank with the spark plugs out, but doesn’t with the spark plugs in.
I can turn the engine over easily by hand at the PTO with the spark plugs out, and naturally it gets hard when it hits compression with the plugs in, but you can still push it over compression slowly by hand.
There is no excess oil in the cylinders when it cranks with the spark plugs out.
The starter pulls 59 amps at 11.2 volts with the spark plugs out, I have seen 300 amps with plugs in and the voltage drops to about 9.5 - 10 volts.
If I time it right and get it spinning with a compression gauge in one cylinder, the compression is 150 psi in both cylinders.
If I put 1 spark plug in and the compression gauge in the other cylinder, it gets to about 55 psi on the compression gauge and the starter stalls.
I have bypassed all the solenoid and battery wiring by using heavy duty jumper cables directly to the starter motor.
With the battery wiring and solenoid connected, the solenoid would just cycle by clicking in and out, without turning the starter.
The armature has been machined and undercut and I checked the armature, there is no variation between segments at 0.010 ohms and no variation in readings horizontally apposed. I also checked the resistance in the same position as where the brushes run and there is no variation in the readings. There is open circuit between all the segments and the armature shaft.
If anyone has any suggestions on how to fix this problem, I would be extremely grateful.