98 SeaDoo GTI 720 low power on the water

[gnygren]

I have a 98 GTI that has no snappy power. Almost everything new. It starts good and seem to rev up good on the trailer but in the water it just feels slugging and when I first went out it would get up to 15 to 20 mph but after riding a bit would only get up to 10 to 15 mph. It seem to run ok and smooth but low power. A couple time when idling it would pop and stall. But mostly runs and idles good. I think it may be something electrical but don’t want to just buy an MPEM for nothing. One odd thing I came across when testing the voltage regulator/rectifier. I have 13.6 + volts from the regulator to the MPEM but when I check the voltage at the battery with engine running it was only 12.6.So it appears like the power is not getting through the MPEM to charge the battery. Also the fuel gauge isn’t working. I don’t know it that’s related. This is what I have done
- rebuilt engine from SBT
- new rotary valve and cover to spec
- rebuilt carb. Also bought new carb and same problem.
- replaced all fuel lines and cleaned selector.
- jet pump seems good and replaced wear ring.
- swapped coil and plugs from other matching.

any help or advise from you wizards here would be greatly appreciated.

 

[mikidymac]

Have you checked compression?

Are you 100% rotary valve timing is correct?
Did you rebuild the carbs with verified Genuine Mikuni parts?

 

[gnygren]

through

Have you checked compression?

Are you 100% rotary valve timing is correct?
Did you rebuild the carbs with verified Genuine Mikuni parts?

I have not checked the compression as it’s a new motor but could do that. I did use a mikuni kit from the dealer. Also bought a new carb as I was convinced it was carb related but they both do the same. I’m fairly confident that the rotary timing is good.

 

[Ckrawiec]

Have you checked the voltage on the Red/purple wire between the mpem and the solenoid....that's where the 14V should be if the RECtifier voltage is getting though......fuses good???...I believe there will be a 15 amp on the mpem and a 15 amp in the rear electric box (mind you..... i'm looking at a 97 wiring diagram but they should be somewhat similar to a 98).

The POP & Stall is suspect......a POP could have been a backfire.....excess fuel in the exhaust.....leaking needle/seat in the carb letting excess fuel to get into the piston and pushed out...you might be running rich.

My guess is the carbs need a little more love......

 

[gnygren]

Thanks for the help. I have retested and I think the power is getting through the MPEM ok to charge the battery. My gut says carb but I’ve been through the 2 carbs now several times and the problem won’t go away. Could the MPEM cause these symptoms ?

 

[SIMPLEARKANSAN]

Did you already replace the MPEM, or perhaps the previous owner did with an aftermarket MPEM?

 

[gnygren]

I believe the MPEM is OEM but a diode was replaced in it a couple years ago. I guess I may have to try a new MPEM next or pull the carb again. Hopefully the video will help with diagnosis. Here is a link to a video of the machine running. I rev it up good and then slowly turn down the idle until it pops and stalls.perhaps it is running rich. It does seem to smoke a lot.

 

[gnygren]

Where is the best place to get a good used OEM MPEM. part number 278 000 916

 

[mikidymac]

Westside Powersports Seadoo.

 

[gnygren]

Westside Powersports Seadoo.

Thanks. I’ll check that out.