96 spx performance issues - need advice

[k_dog345]

Hi, I just finished rebuilding my carbs, fuel system, and replaced my rotary valve cover. My ski runs like a dream when it is running high speeds. But if I let it idle for more than a few seconds, it will start to hesitate on me and want to die. Occasionally it will die, and start up becomes hard. I have to apply full choke and a lot of gas to get it to fire and move past the dead spot. But then runs great again!

Plugs are showing me a rich condition



I’m not well versed tuning carbs, but I think I need to adjust the low screw? Advice is appreciated.

 

[mikidymac]

Sounds like your needles and seats are leaking. Did you use Genuine Mikuni parts and check pop-off and leak down?

 

[k_dog345]

Sounds like your needles and seats are leaking. Did you use Genuine Mikuni parts and check pop-off and leak down?

Ugh, that is not the news I wanted to hear. Yes, I used genuine mikuni parts, I checked pop off (and struggled with it, see: 10 psi pop off difference between mag and pto). But I have not performed a leak down test. I also got a new needle/seat. But I couldn't use the new seats, the o rings were too big and I couldn't get them to seat. When I was checking the pop off pressure, I used plenty of wd40. I did not notice any bubbling around the seat, but I wouldn't doubt that maybe that's what is happening because I had to reuse the old seat and oring. So, you're pretty positive it wouldn't be something else? And where should I order another needle/seat if so... I got the needle/seat from Bay Area Powersports on Amazon.

 

[mikidymac]

I have never seen a Genuine Mikuni needle and seat not fit.
Yes they need to be replaced and you should not have 10 psi difference between carbs.

 

[k_dog345]

I have never seen a Genuine Mikuni needle and seat not fit.
Yes they need to be replaced and you should not have 10 psi difference between carbs.

Mikuni Twin Carb 2 Pack Needle Valve Seat Kit Sea Doo HX SPX GTI XP

This is what I got, reading closer, looks like it's "OEM Quality aftermarket". I'm not sure where to find the genuine needle/seat either, my google searches have turned up nothing for me. Any suggestions on where to get a replacement needle/seat?

 

[mikidymac]

There is your issue for one. Aftermarket is junk.

Here is a link to Genuine Mikuni but the inventory from everyone is low so not sure what is up with the supply chain at the moment. Mikuni 1.2.

 

[k_dog345]

There is your issue for one. Aftermarket is junk.

Here is a link to Genuine Mikuni but the inventory from everyone is low so not sure what is up with the supply chain at the moment. Mikuni 1.2.

Thanks again! Much appreciated

 

[JeremyD615]

Just for future reference, the needles and seats should always be kept as a set. Don’t put a new needle in an old seat, as you’ll have issues like this...

 

[k_dog345]

Just for future reference, the needles and seats should always be kept as a set. Don’t put a new needle in an old seat, as you’ll have issues like this...

Word. This is exactly what I did! I'm a little confused though, if needle and seat were leaking wouldn't that mean I have flooded carbs? As I said, it took full choke and throttle to get the ski to start again and run up past the dead spot. If the carbs would flooded I would think that giving gas and choke would make the issue worse....


To clarify, if I idle for more than a few seconds it will continue to idle fine. But when I go to take off, this is when the hesitation starts and stall likely happens. And then it is hard to start. I realize my initial wording may of sounded like the ski would start to hesitate and stall at idle. It's only when I attempt to give it throttle out of idle after idling for some time.

 

[JeremyD615]

I’d suspect that the needle may be sticking in the seat rather than leaking...

 

[djcarter]

Sounds like your needles and seats are leaking. Did you use Genuine Mikuni parts and check pop-off and leak down?

Do you guys have a link for instructions on checking pop off? I too have a 1996 SPX Im trying to get running after an engine rebuild. I plan on rebuilding the carbs and want to check all this after rebuilding them.

NVM I found your carb rebuild post @mikidymac. Very nice, thank you for taking the time to post that.