1998 Seadoo GSX Limited with slow irregular crank. New fully charged battery. After about 4 cranks it will start but runs rough and backfires occasionally. I can take the ground wire and connect to battery and connect a jumper from positive side of battery to starter side of solenoid and the engine turns over at a rapid pace like normal. Plugs in or out doesn’t matter when attempting to start normally. I’ve ruled out the starter, made sure my reed valves were good, swapped starter solenoid. Checked all grounds and cleaned all connections. I’m thinking it’s something to do with the ignition system or woodruff key. When I put a voltmeter on the battery side of the solenoid I get 12 volts. When I put the voltmeter on starter of the solenoid and push start I get 12 volts initially and then the numbers bounce all over the place. The jet pump isn't installed. Could it be the start/stop switch, but that wouldn't explain the engine backfire.