1996 XP losing speed/dies at extended throttle.

[thzpcs]

Just trying to sort out kind of a weird issue I've been having with an XP I've been working on over the season.

I just put a new motor (165PSI in both cylinders) in it with freshly cleaned and rebuilt carbs. Mikuni kit, popoff on both carbs right at 29PSI. LS needles at 1-1/4, HS at 1/4. Replaced all the Tempo lines. No mods of any sort. Still running the oil injection pump, not premix, and I've verified it's working correctly.

Idles great, runs great, tons of fun. Up until you try and run it flat out at 100% throttle. There's tons of power down low, and it'll rev right up and get to 53-54MPH, but it just can't hold top speed. It'll just slowly lose power and keep bogging and bogging until it dies. When restarting, you have to flutter the throttle a bit, but it'll start right back up like nothing happened, and go on its merry way.

I'm still pretty new to these things, so I'm at a bit of a loss as to what might be the issue, as basically everything I've seen says it should be running well. Any thoughts on what I might want to check?

 

[2strokeboy]

have you redone the fuel lines or are thy grey tempo lines and do you have any fuel filters other than the stock one

 

[thzpcs]

have you redone the fuel lines or are thy grey tempo lines and do you have any fuel filters other than the stock one

Yes, as mentioned, I've replaced all of the grey Tempo lines before I rebuilt the carbs. I don't have any fuel filters other than the ones inside the carbs themselves, and the stock water separator, which was cleaned out before the rebuild and I also checked it again once I started having the issue, and there was nothing I'd noticed.

 

[2strokeboy]

Yes, as mentioned, I've replaced all of the grey Tempo lines before I rebuilt the carbs. I don't have any fuel filters other than the ones inside the carbs themselves, and the stock water separator, which was cleaned out before the rebuild and I also checked it again once I started having the issue, and there was nothing I'd noticed.

what year xp is this

 

[burtshaver2021]

Sea Doo PWC Carburetor Reference
It says here that the high speed screw should be at 0 turns out and the low speed screw should be at 1 turn out.

 

[etemplet]

Get that Pop-Off set to around 37psi. The black 80 gram spring and new needles should do the trick. It's probably too rich. I chased two GTXs adjusting the carbs. I went from 23psi to 36-38. World of difference. 30psi didn't get it done..... 33psi didn't get it done. 38psi and VROOM !!!

 

[etemplet]

Sea Doo PWC Carburetor Reference
It says here that the high speed screw should be at 0 turns out and the low speed screw should be at 1 turn out.

Some people give the rear cylinder a 1/4 turn on the high speed. 1/4 turn will richen it up a bit though and I think he is already too rich with the pop-off setting. On a side note... this year... both GTXs are FLYING !!! My wife's bumped 53mph and mine hit 52 on the GPS which is great for that ski. Gotta check thos spark plugs. I always thought both my GTXs were rich reading the spark plugs but I wouldn't drop the jetting down from factory stock.

 

[thzpcs]

I guess I'm just super worried about running too lean and screwing something up. I'm curious about what the throttle should feel like as well, as it seems like there's a distinct "step" in mine around 1/3-1/2 throttle where there's a very distinctive increase in acceleration as well. It's not like it's unresponsive at the low end, but there's definitely a point in the throttle where the acceleration profile changes. Similarly, if it's set correctly, should I be able to just go from 0-WOT and there should be zero hesitation at all? If I've been idling/at < 1/4 throttle for a bit and then go 0-100%, it'll usually stumble a bit unless I "clear it out" with a couple of quick chops of the throttle. Then it'll accelerate no problem, unless I let it idle for a bit again.

I tried setting the pop-off, and the LS needles with the carb tuning thread and using the choke to see if, when it bogs, it picks up/dies, so it felt like I set those pretty well. My concern was that when doing the test runs, looking at the plugs, I'm only seeing coloration on the electrodes, and not on the whole face of the plug like I've seen in pictures. I don't know if I'm just not running long enough or what, but like I said, I'm new to this and want to play it safe to avoid another engine mishap.

 

[burtshaver2021]

I guess I'm just super worried about running too lean and screwing something up. I'm curious about what the throttle should feel like as well, as it seems like there's a distinct "step" in mine around 1/3-1/2 throttle where there's a very distinctive increase in acceleration as well. It's not like it's unresponsive at the low end, but there's definitely a point in the throttle where the acceleration profile changes. Similarly, if it's set correctly, should I be able to just go from 0-WOT and there should be zero hesitation at all? If I've been idling/at < 1/4 throttle for a bit and then go 0-100%, it'll usually stumble a bit unless I "clear it out" with a couple of quick chops of the throttle. Then it'll accelerate no problem, unless I let it idle for a bit again.

I tried setting the pop-off, and the LS needles with the carb tuning thread and using the choke to see if, when it bogs, it picks up/dies, so it felt like I set those pretty well. My concern was that when doing the test runs, looking at the plugs, I'm only seeing coloration on the electrodes, and not on the whole face of the plug like I've seen in pictures. I don't know if I'm just not running long enough or what, but like I said, I'm new to this and want to play it safe to avoid another engine mishap.

Did you try putting the high and low speed screws to factory settings 1 turn out for low and high at 0? What happened to the original engine? Just want to be sure the same doesn’t happen to your new engine.

 

[thzpcs]

I've not gotten a chance to

Did you try putting the high and low speed screws to factory settings 1 turn out for low and high at 0? What happened to the original engine? Just want to be sure the same doesn’t happen to your new engine.

I've not gotten a chance to adjust the high speed yet, but I had adjusted the low speed to where they're pretty close to 1, and it seems to be running well there, aside from the issues mentioned in the thread.

As for what happened with the old engine, I really have no idea, which is why I'm so concerned.

I got the ski "free" with a trailer, as the guy needed the room and couldn't get the thing running. It was in good shape overall, 170psi on both cylinders, gauges and VTS working, XPS oil in the tank, but was just flooding with fuel, so I changed the hoses and rebuilt the carbs with a Venom kit (Yes, I know) and had it out for one of the best days I've ever had on the lake. It ran extremely well, hitting 53MPH on the GPS, but would bog and die if you idled it too long. Reading about the issues with Venom kits, I bought Mikuni stuff, rebuilt them again, and then tried to take it out the next day. It started fine on the trailer, but when I put it into the water it wouldn't start. Took it out, brought it home and charged the battery up, tried starting it again, and after a couple of tries I noticed the exhaust pitch suddenly shift. I take the carbs off, and to my horror I find metal shavings in the mag side intake. Check compression, it's about 90-100PSI, so something is clearly wrong and I just decided to swap the motor with a very low hour fully assembled OEM motor a buddy had parted out of a GTX.

When I got the motor out, the hull was filled with oil, as I stupidly didn't realize there were 2 oil lines, and only pinched off the one to the pump before disconnecting all the hoses, and basically the entire oil tank had drained into the hull. Got the engine out and as I drained the hull, and I find just how fucked it was when I find a chunk of the block under all the oil, certainly explaining the change in pitch.

Like I said, I have no idea if it was something that I did, or if I just somehow got really unlucky and it just happened to be on its last legs when I got it. It still had the Tempo lines, so it could've been running really lean for a long while before I got it, but it was just so odd to me that it would just suddenly and catastrophically fail like that, just from cranking on the trailer.

After putting the new motor in, I rechecked all the passages and popoff on the carbs before installing them, and the popoff was set as mentioned and screws set to factory, hence why I wanted to err on the side of caution and go richer. I just really couldn't tell with the top speed issue, as I've never had speed "fall off" like that, and again, got really worried I was going to grenade another engine.

 

[POPPS]

you need the OEM mikuni carb kits!,,,aftermarket,,,NEVER WORK.

 

[thzpcs]

you need the OEM mikuni carb kits!,,,aftermarket,,,NEVER WORK.

I'm well aware of this now, hence why, even though it was actually running decently, I re-rebuilt them with all Mikuni parts.

 

[thzpcs]

So, just as an update for everyone on this issue, I think that I've got it figured out.

It seems that the bolts on the exhaust flange right above the airbox had worked loose a bit, and so there was a pretty significant exhaust leak there. My guess is that, in addition to the lack of backpressure and such, the engine was obviously not super happy about breathing in exhaust gas. It makes sense that it'd generally be okay at lower speeds for short bursts, but for extended WOT runs, it was just filling the hull with exhaust and depriving the engine of oxygen. I tightened those up and it's right as rain, hitting 51MPH no problem on the water.

I also adjusted the HS needles back, to 0 on the mag side and +1/8 on the PTO which seemed to help as well, as it got that extra 1MPH over 50 when both were at 0.

Probably still need to play with the popoff and low speed a bit, as it definitely seems to be running really rich on the low end now, but now I'm far less concerned about the thing blowing up or seizing on me.

 

[burtshaver2021]

That’s good that you got it figured out, Seadoo source says pop off should be 23 to 43 pounds for a 96 XP, you had mentioned yours was popping at 29 which is probably a little low, I’ve never bent the arm on a carb yet, just found that when I order new needle, seat and spring from OSD Marine that they always seem to pop at the higher end of the scale.