96 Seadoo GTX misfires through the carb

[TimJ]

I have just finished rebuilding the engine on a 96 Seadoo GTX. The engine starts and idles but when the throttle is opened it backfires through the flame arrester and then dies. Thinking it was a lean condition I be been through the carbs a few times now but it is always the same. I have also checked the rotary valve timing twice! And it’s spot on. I used a timing light to check the ignition timing and I found that when it backfired the timing light picked up the mark on the PTO about 40 degrees retarded. So I then thought that perhaps the trigger coil was defective. When I was rebuilding the engine the stator and pickup did show signs of possible water damage. I bought one of the cheap stator and trigger coils of eBay to give that a try and now ther is no spark at all. I will start faultfinding the no spark but thought it might be useful to post this to see if anybody has had a similar problem.

 

[mikidymac]

The aftermarket electrical parts are junk.

 

[POPPS]

As miki would ask,,,"did you use genuine mikuni parts?"

 

[TimJ]

Yes genuine mikuni parts for the carbs but a cheap knock off for the replacement trigger coil.

 

[POPPS]

AM electrical are a gamble,,,do a resistance test on the pickup,and your stator,,,, don't have the specs off hand,,,if it starts well,,,it is probably is not timing,,,best move is follow miki's carb thread with the genuine kit,,,that is easier than pulling the front cover,

 

[TimJ]

Thanks for that. The trigger coil resistance is within spec as are the stator windings. The problem now is that there is no spark. My next step is to confirm all of the wiring. The front electrical box is grounded through the stator core so maybe that’s the problem. Or another wiring fault that was partial before I changed the stator and pickup. Or the more obvious that the new stator and pickup are no good. I didn’t check the magnet before I fitted it. Anyway I’ll keep the post updated when I get a chance to get down and do some more fault finding. I would be really interested if anyone has experience of a backfire through the carbs associated with the trigger coil, CDI or wiring. I am chasing this down because I saw the ignition timing retard drastically when the engine was reved up. This coincided with the backfire exactly. I was using a timing light on the mag spark plug lead. As always I might be missing something here!

 

[mikidymac]

The aftermarket electrical parts almost never work.

 

[TimJ]

I got some fault finding done on the no spark with the new cheap trigger coil and stator. Whilst I haven’t tested it yet I am pretty sure that the no spark was caused by the bracket supplied with the trigger coil. It caused the sensor head to be about 5 mm further away from the protrusions on the flywheel rotor than the OEM part. So I have swapped the brackets around and will retest. I confirmed all of the wiring associated with the ignition system and all was good. I measured the resistances of the CDI and compared them to the manual. The resistances were very different. Has anybody measured the resistances of a 96 GTX CDI in line with the the manual before? I would be interested in your findings. Even better does anybody have an internal schematic?

 

[TimJ]

Hi Guys to wrap this one up the ski is running great now. When I changed over the brackets on the trigger coil it sprang to live and reved out nicely with no backfire. Points to note are:
A faulty trigger coil can cause the CDI to randomly retard the ignition timing when the revs are raised causing the fuel to ignite in the crank and backfire through the flame arrester.
The cheap knock of trigger coil and stator windings do work but the mounting bracket is wrong on the sensor and the cable lengths on the windings are too long. Both corrected and I let them know!