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  1. #1

    Question 951 & 787 Ignition Timing Curve Difference

    Just wondering if anyone knows the difference between the ignition timing curve from a 787 to 951 carby engines.

    Checking the specs between the 2 motors I can't see any differences, but the timing curve I'm guessing maybe different.

    I'm putting in a newly rebuilt 787 into a 2000 RX which has a completely unrepairable 947.
    I still want the Tacho, Speedo Fuel Gauge, VTS etc working otherwise I would just replace the electrical box.

    There are a few other modifications obviously between fitting the 787 but we've already sorted them.

  2. #2
    You would be much better off selling the 787 and buying a 951. The electronics are different, motor mounts, pump, etc. I would also think you would have a tough time selling a 787 RX.

  3. #3
    Don't forget that the 2000 RX MPEM is two-coil; all the 787 carbs are single. You would need to put a 951 twin mag cup (off your old 2000 engine or any 99+ 951) on the 787 engine.

    Timing curve is different. You probably would be close if you lost the TPS, which kicks in the retard to protect the 951 thru the lean band.

  4. #4
    Thanks for the info Sea Dood. I'm guessing you mean the Magneto cover as the 'Mag Cup' (sorry just trying to be sure). Are they fine to interchange, I do have that still left from the old 951.
    The TPS I haven't seen that yet but have read about them. If it was left as is what effect would that have on the 787. I expect lean means it could burn out pistons if left connected or would it make the motor run rich?

    Am I on the right track?
    Anything else you can think of that may give me problems?

    I accept what Wire4Money is saying but getting hold of a going 951 in OZ is near impossible, plus I don't expect to be worrying about resale price of a 2000 RX with a 787, more I'm trying to make good of the situation (a good 787 and a blown 951).

  5. #5
    By "Mag Cup", I am referring to the magnetic rotating assembly that is attached to the flywheel and encircles the stator. Your 2000 RX engine has part number 290887945 for the mag cup (look it up in the parts diagram so you can see what I am talking about..). You need to take this cup off your blown 951 engine and install it on your 787 engine to run a two coil ignition MPEM like your RX has. They are interchangeable.

    I have no idea about the comparison between the two ignition curves, but you better check them out before you end up blowing up the 787...If you were really industrious, you could plot out the ignition curve on a 787 engine, take readings at idle, 3K RPM, and redline (7100 or so) and then do the same with a 951 engine. This would give you a good idea if you are in the ballpark. Somebody like Bill O'neal might know the comparison between the two.

    The TPS just tells the MPEM when the throttle has been given 80% or more throttle, and the MPEM retards the ignition timing slightly. They did this in the 99+ skis to help keep the 951 from blowing up. You probably don't need this for the 787.

  6. #6
    Thanks again Sea Dood your help is excellent and appreciated.
    I had a look on the 951 Mag Cup and notice it has 4 trigger points, 3 narrow and 1 wide, I guess the 787 Mag cup has 1 wide and 1 narrow?.
    Is the Trigger Coil the same between the 2 motors?

    I guess one option may be to use both MPEMs and perhaps just supply some power and the ignition trigger to the 951 to work the Tacho & the other guages and let the 787 MPEM do the ignition, charging etc and nothing out to any guages.
    The only thing would be the Starting and which MPEM controls Anti Theft switch???
    2nd option may be to get a MPEM from a 2000 GTX/GSX and hope they use the same Guage?

    Would retarding the motor at 80% or more throttle via the TPS be a bad thing?

    Definitely the simplest would be to use the 951 MPEM initially.

    Who is Bill O'Neal, how do I contact him?

  7. #7
    Bill ONeill is the owner of Watercraft Magic in Glendora California. He is an awesome source of info for the 2 stroke Seadoos. He has his own section over at I have used his services for rebuilds and upgrades to my 951 carbs withgreat results.

  8. #8
    thanks tjcin I will look him up.

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