Engine swap now engine backfire

[wvdealz]

My 951 in my 2000 XP got toasted at the end of the summer. I came across a 1999 XP Limited with a great running motor (ran it before removing it) and completed an engine swap. I went ahead and changed all the grey fuel lines and rebuilt the carbs with Mikuni carb kits. Finished getting it put back together today and when I try starting it, it won't start and backfires. First backfire was moderate, but second was as loud as a gunshot. I didn't touch the donor engine, left it sealed and swapped no parts since it ran perfect. Did I miss something and does anyone have any suggestions? I thought about changing the MPEM, but they are actually different, instead of having 4 plugs, the 1999 only had 3 due to being the LTD. Any help would be appreciated.

 

[Coastiejoe]

[MENTION=41828]Minnetonka4me[/MENTION] may be able to help in regards to the MPEM.

I have to think some sort of input to the timing is the issue. [MENTION=31048]LouDoo[/MENTION] also has very good 2-stroke knowledge...

 

[Sportster-2001-951C-Stock]

The 1999 was dual coil just like the 2000, right? Sounds like you got the two plug wires crossed? I'm not aware of any differences in timing pickups, there are two trigger magnets on flywheel.

Is it possible a screw fell into the intake and is holding open a reed valve?

 

[wvdealz]

Not much chance of coil wires getting crossed. They 2 different length and one cannot reach the other plug. Motor was lifted from one ski and set on workbench, carbs removed, rebuilt and installed..not much chance for anything falling into reed valve, but if I end up tearing into it, I will definitely check

 

[Minnetonka4me]

I wonder if it was a 98 XPL you got the motor out of....that is the only thing that makes sense. Did you use the flywheel and mag cup off the replacement motor or out of the 2000?

 

[wvdealz]

Update, I put the MPEM from the 99 (it has 2 plug ports instead of 3), I had someone offline tell me he thinks the 3rd is for guages only. I plugged it up and the ski fired right up. I used the mag cup and all motor parts from the 99...do I need to change the mag cup/flywheel or any other parts from the 2000 to make my 2000 MPEM compatible or is my 2000 MPEM roached? If so can I swap the wiring harness so I can use the 1999 MPEM?

 

[Sportster-2001-951C-Stock]

My plug wires are different length too, but I can swap stuff from side to side (did this troubleshooting a miss once).

The difference must be the ignition pickup, ie: location of the magnets on the flywheel. Sounds like you'll need to either transfer the MPEM and possibly harness from the donor or flywheel timing stuff from the old motor to the new one.

I'd swap the flywheel just to keep the 2000 stuff but that's me.

 

[wvdealz]

Is it usually necessary to swap the stator and flywheel when doing an engine swap? The part numbers are the same on these parts for both engines, but are the magnets different on the flywheel despite the same part number?

 

[Minnetonka4me]

That's a 98 if it only had 2 connectors. 99 would have had 3. Switch the flywheel. The pickup is fine, just the flywheel. Well technically you need to swap the mag cup but if you do that you should replace the bolts bc they are stretch bolts.

 

[wvdealz]

Actually the 1999 Limited has 2, it was different for the regular XP. The MPEM for the 99 limited only fits a 99 limited.

 

[Minnetonka4me]

You are incorrect sir. The 98 had the 2 plug MPEM and single coil, 99 and up had 3 plug MPEM and 2 separate coils. Not to act all high and mighty....but I know what Im talking about. 100% positive.

 

[wvdealz]

I got my information from http://www.seadoosource.com/mpemref.html Shows the 99 Limited stands alone for the MPEM, only year that takes that MPEM. The regular 99 XP is the same as 2000-2002. Anyways, great news...I swapped the flywheel and the motor runs perfect now.

 

[AdamXP800]

You ever seen that commercial, "it has to be true, I read it on the Internet" lol
Good news is you got it running

 

[wvdealz]

I'm not sure what is accurate but I can say for sure that the title to my donor ski said 1999 Sea-Doo limited. Just excited I fixed the money trap.

 

[AdamXP800]

I've seen a Gtx titled and an Spi before, nothing surprises me

 

[jhjesse]

Vin # on the ski will tell all no matter what the title says and Minnetonka is correct 98 had single coil 99 and up had two coils. There have been countless threads on 951s backfiring due to part swaps from 98 to 99.

 

[wvdealz]

VIN says 99 too. The donor ski had 2 coils.

 

[Minnetonka4me]

Ok it woulds like it was a 99 machine someone put 98 electronics into then. Does the donor ski have 2 big connectors or 3 for the mpem? I would be hard pressed to believe the 99 wiring would work with a 98 XPL, but I cant say I've ever tried it.

You need to re-read that link you posted, he has 98 XPL listed twice, then 99-02 XP. 98 is the one year one model part...like I said.

 

[wvdealz]

Just the 2

 

[Sportster-2001-951C-Stock]

Is it usually necessary to swap the stator and flywheel when doing an engine swap? The part numbers are the same on these parts for both engines, but are the magnets different on the flywheel despite the same part number?

Depends on the electronics being used. I'm no seadoo motor swap guru but I've swapped enough motors in enough boats to know when they pop and backfire there's a timing issue of some sort and the 951 is a reed motor so the intake valve timing is always correct (assuming reeds aren't broken) thus this must be an ignition timing issue.

I can't tell you which flywheel your donor motor has but seems likely to me it's incompatible with the electronics.

So you have a choice to make, IMO, then live happily ever after.... .

 

[wvdealz]

One more question...jetski runs perfect now but while I was working on the ski, I noticed the wires to the simp pump were cut so I spliced them back together. Now, as Soon as I plug in the dess key, the sump pump hums for a few seconds, then quits. Any idea what may be causing that now? The previous owner must have cut the wires instead of fixing the problem.

 

[Sportster-2001-951C-Stock]

I got my information from http://www.seadoosource.com/mpemref.html Shows the 99 Limited stands alone for the MPEM, only year that takes that MPEM. The regular 99 XP is the same as 2000-2002. Anyways, great news...I swapped the flywheel and the motor runs perfect now.

Nice, good to hear. So were you able to confirm by part number on the wheels they're not the same, or if the trigger magnets are positioned differently? Of course I'm curious about that.

 

[Sportster-2001-951C-Stock]

One more question...jetski runs perfect now but while I was working on the ski, I noticed the wires to the simp pump were cut so I spliced them back together. Now, as Soon as I plug in the dess key, the sump pump hums for a few seconds, then quits. Any idea what may be causing that now? The previous owner must have cut the wires instead of fixing the problem.

Some pumps have pretty crazy electronics in them now, they will come on briefly when they 1st receive power (even the type with mechanical float switch). The old (reliable IMO) pumps had no electronics inside, just a mechanical float switch and as long as that switch was open (float at the bottom) the motor never ran.

Some of the newer pumps have an internal timer and current sensing circuit where the timer automatically kicks on the motor periodically and if the current sensor senses no load the motor is turned off after a few seconds. If the current sensor senses "abnormally high" current it keeps the motor running till the current drops off to normal (load on motor means water is pumping).

Like I said, new pumps are whacko! (possessed?). Rube Goldberg would be proud.

 

[AdamXP800]

One more question...jetski runs perfect now but while I was working on the ski, I noticed the wires to the simp pump were cut so I spliced them back together. Now, as Soon as I plug in the dess key, the sump pump hums for a few seconds, then quits. Any idea what may be causing that now? The previous owner must have cut the wires instead of fixing the problem.

This is correct, the bilge pump should cycle when you hook the key on

 

[wvdealz]

Yeah, the 99 flywheel had 2 long magnets and the 2000 had one long and 3 short magnets.