MPEM 951 to 787 motor swap

[Hollymax0428]

Hello all, I have a question that searching doesn't really clear up.

I have a 2000 RX Jetski that has a blown 951 engine (peice broken out of the side of the casing bottom end). I also have a 1997 787 recently rebuilt motor.
Apart from the front engine mount & the exhaust on oppsite sides (which shouldn't really be a big problem), I hear a lot of talk about having to change electricals.

My knowledge on the Electrical box and the MPEM is a bit limited, but apparently the Magneto on the engine tells the Electrical box when to send power from the coils to the Spark plugs, via the polarity change and does the battery charging.

The rest of the MPEM appears to be for the guages, vts and some engine management like the rev limiter & overheating.

The specs for the electrical side, spark power, battery charging, rev limiter etc all seem the same between the 951 & the 787, but I'm not sure of the spark triggering.

If there is something specific to each of these motor not shared I would probably have to get the Electrical Box or MPEM or both from the GTX or similar that had the 787, but not sure.

Any help in this area would be appreciated

 

[seadooya]

from what i've read, you use the flywheel and mag cup from the 787, and all is good then.

my bad, this is for to run a 951 motor....i got a mpem from a 97spx(787) w/programmed key, if interested...pm me

 

[Hollymax0428]

Thanks seadooya, I have the MPEM & key from the 787, but I would be pretty sure it won't run the Gauges etc.

I've read about changing the Mag Cup but not sure what effect this would have, or why it would be required to make it work (lack of knowledge here).

I would have thought when it needs to fire the spark plug would be very similar between motors and the rest of the electrical specs seems either the same or similar?

 

[seadooya]

ur dumping the 951 and going to the 787 correct?..then install the 787 electronics, and depending on the gauges, only one that would really matter is a rpm gauge, which the "grey" wire controls it, or just wrap it around the mag plug wire...if need be, i got a fuel/oil gauge and speedo gauge too.
:cheers:

 

[Hollymax0428]

ur dumping the 951 and going to the 787 correct?..then install the 787 electronics, and depending on the gauges, only one that would really matter is a rpm gauge, which the "grey" wire controls it, or just wrap it around the mag plug wire...if need be, i got a fuel/oil gauge and speedo gauge too.
:cheers:

Correct going from 951 back to 787, but I have to keep the VTS, Tacho, speedo, fuel etc. working which I think I will need the 951 MPEM.

I suppose I could use both, although I'm not sure it is the rear electrical box that is more important or the MPEM. I'm guessing the MPEM advances/retards the spark discharge via the Electrical box.

The way I see it at the moment using the 951 MPEM, the only a difference could be the timing of the spark. The rest I can't see would effect the running of the motor. What do you think?

 

[seadooya]

coils' always firing..180*, so dont think it be the issue, but the whole enchilata of the woking of it for a 951, just dont see it communicating with the 787...

People will run the 787 flywheel in the 951 motor, cuz they go with the MSD enhancer, eliminating the mpem, but your situation is dif'rent.

The tach, you can use the grey wire from the mpem or wrap the grey wire around mag wire, because the purple is 12v constant..backlight, and black is ground, and VTS, yeah it be nice, but you can zero/lock it out...

What yr/mdl ski your mpem come from?

 

[Hollymax0428]

That's what I probably don't see, when it comes to 2 Strokes I'm a bit lost, no distributor etc. as to what the actual motor side of things affects the MPEM.

There is only the plug on the Mag & an Overheating Warning wire and the Starter Motor Wire that comes off the motor. The rest is self contained as far as the motor going. The Plug from the Mag has charging wires to recharge the Battery and one or two trigger wires for the spark (i think).

In the MPEM I'm guessing it can alter the timing & read the spark count through the tacho (which would also put a rev limiter) and stop anyone starting the motor without the key. The rest seems to be for other parts, speedo, fuel guage etc.

What's the MSD enhancer?

Sorry just noticed, it is a 2000 RX