1993 SeaDoo XP - Engine missing, possible fuel starvation?

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Spunbearing

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Hi everyone,

I am hoping you can help me out with a problem I am having with my 1993 SeaDoo XP. This thing has been my go-to-Doo when my other ones need work and now it is the one acting up. It runs fine on the hose but when I put it in the water anything over 1/4-1/3 throttle makes it sound like one of the cylinders is missing. If I give it full throttle it accelerates for about 1 second like it is running perfect and then goes back to sounding like one cylinder is misfiring. It idles and starts without any issues. I think it is not getting enough fuel to the MAG side carb due to fuel starvation but it could be anything at this point.

Here is some back story, it was fogged and winterized but left in storage due to life events for 4 years. Last year I took it out for a run for the first time and it ran amazing on the hose but in the water it was bogging (pop-pop noise, engine misfire) when giving more then 1/3rd throttle. I pulled it out and cleaned the carbs over the winter. I used my ultrasonic cleaner, carb picks and compressed air to make sure it was spotless. I expected to see them gummed up but they were actually clean to start with. The Low-speed needle is 1-1/4 turns out, high-speed is closed and pop-off set to 26# per factory settings. Jets and intake are stock factory size. When I originally picked up the unit I rebuilt the carbs with Mikuni rebuild kits but kept the original float springs because the ones in the rebuilt kits are wrong. The filters in the carbs had some sediment in them so I cleaned them out. I put the carbs back and but I am still having the same problem. I forgot about the spin off fuel filter so I pulled that out and it was clean but the o-ring in the filter popped out of the groove and would not go in because it has expanded. A new one is being ordered so I can reinstall it. I also removed the fuel selector switch and verified that it is clean. All of the grey fuel lines were replaced a long time ago with fuel injection lines and the gas tank holds pressure. The fuel tank pickup with fuel level sensor is also less than 10 year old. I am using no ethanol gas but I did not drain the little gas left in the tank, instead adding fresh gas with it. I thought it could be old gas but at this point I have run about 10 gallons through it with no change in the throttle response. The gas in the tank does not smell “old” or look discolored, there is no sediment or buildup at the bottom of the tank. Changing the fuel selector to/from RES has no impact on the performance.

Thanks,

Spunbearing
 
Check the fuel selector switch (ON/OFF/Reserve) it often gets clogged. I ended up just bypassing mine and never had an issue after.
 
Thanks for the reply Feeze68. I was reading about that issue while doing "research" so I replaced it with a new one. No change :(

So I am looking through possible causes and I am wondering if the head gasket is leaking water into the cylinder. Is there an easy way to check for this without taking the head off? I was thinking I could floor it till it bogs, kill the engine and pull the plugs to inspect for water infiltration. I also need to check cylinder pressure. Another thing I thought I would check is the pickup tub in the gas tank for clogs. There was one post of a bug being in the tube on someones so i thought i would make sure mine is clean. I have also heard rectifiers can go bad and cause issues with the spark at higher rpm. I think I replaced mine already a while back but I can double check it. I only see the 'Doo every other weekend to it is hard to get time to test it. Oh well.
 
I got an hour away from the family to look at the 'Doo so I hooked it up to the hose to see if I could see any water leaks anywhere but everything looks good. I took the gas tank out to check the fuel pickup and everything was clean, the screen on the bottom of the pickup was clean. I drained the gas and cleaned the tank while I was at it but ran out of time to do a water test with fresh gas. The engine revs great on the hose and when I pulled the plugs after there was no signs of moisture and they look good.

Am I right to think that if there was an issue with the rectifier it would show up out of the water as well? I would think because it is electrical and not engine load related it would show up. I will try to do a compression test next time but the way engine starts and idles so well makes me think the compression is good.
 
Finally got a minute to do a compression test, 145.0psi on the MAG side, 145.5psi on the PTO side. Sill not enough time to do a water test yet though, ug.

Can someone please let me know about my question about the rectifier? Would this issue show up while running on the hose? Also, for the fuel return line, about how much fuel actually is going back to the gas tank? When I cleaned the carbs the I made sure I could pass air through there but it was a very very small opening. This is expected, right?

Thanks!
 
A rectifier running issue could show up on the trailer and it could not. You never really know how they’re going to act when they go bad. You can test your voltage while on the trailer though, and it will show an abnormally high voltage, above 14V, when it’s revved if the unit is bad.

Have you water tested after replacing the fuel filter o ring? I really think that’s your most likely issue, as an air leak will cause exactly what you’re experiencing...
 
A rectifier running issue could show up on the trailer and it could not. You never really know how they’re going to act when they go bad. You can test your voltage while on the trailer though, and it will show an abnormally high voltage, above 14V, when it’s revved if the unit is bad.

Have you water tested after replacing the fuel filter o ring? I really think that’s your most likely issue, as an air leak will cause exactly what you’re experiencing...

Thanks for the reply Jeremy! I will check the voltage on the trailer and see what it shows at the battery posts. I did water test it after replacing the o-ring and the fuel selection switch, there wasn't any change. I can check the hoses to see if there is any lose clamps but the hoses are new. I also only run ethanol free fuel and the system looked clean.
 
Ok, finally got the 'Doo back in the water today. I have new gas, new spark plug caps with the wires trimmed and I checked the voltage at the battery with it reved all the way up to make sure the voltage regulator is good. I am seeing around 14.5v. I am still seeing the same behavior. UG!

I basically am circling around back to the carbs. If I hit the choke while at full throttle the engine dies. If I turn off the gas while I am running the engine surges and then dies. From idle if I give it full throttle it takes off and then starts to bog.

How big is the whole for the fuel return in the carb suppose to be? When I was cleaning mine I noticed that it flower a little but not a lot of gas. About how big should it be? I wonder if mine is still a little clogged causing one of the carbs to flood.
 
The hole should be the full ID of the outlet nipple. You want as little restriction as possible in the return.
 
The return is calibrated and restricts flow to keep fuel pressure. It’s built into the body and you can see it gets smaller on the fuel pump side.
 
I didn’t think the early skis had and metering on the return line... Thanks for the correction Miki. I need to go back and look at the carbs on my earlier motors now.
 
As long as it has SBN carbs it has a restrictor. I don’t remember what year they phased out the round body BN to be honest.
 
I guess here’s where I’m confused. Spunbearing, are you saying that the outlet nipple itself is restricted, or are you talking about the orifice inside the carb body?

This is what the “hole” inside the carb should look like, if this wasn’t a nasty scrap carb I had laying around...2A4598CC-FA61-4640-AF6A-3B94B687F161.jpeg

This hole is calibrated for the proper flow. You shouldn’t have anything inside the outlet nipple or line though, unless I’m missing something...
 
Thanks for the replies guys! I was able to get the carbs off and snap a picture of the return hole. It is very small but it appears clean and is flowing air without any problems. I was really excited there for a second, I thought this might be the issue.


Return_Hole.jpg


Is there anything else that could cause a running rich condition? I just went through the carbs again and everything looks good, pop-off pressure is right, etc. etc.
 
Well guys, I finally got it! I was going through the carbs again to see if there was anything I could have missed and there there was! I had the settings on the low and high speed needles reversed! I set them correctly this time and the old XP was tearing it up. I was rebuilding them late at night after getting the kids to bed, I must have been too sleepy to realize the physically larger needle is for the low speed and the smaller needle is for the high speed. Silly me.

Honestly, I don't think it has ever run this well, with the new fuel selector, water filter o-ring and spark plug caps. Thank you all for your help. Here is an action pic for you guys.
SeaDoo_Going.JPG
 
I also wanted to post this incase it helps anyone. The new NGK TB05EMA spark plug caps are way smaller than the old ones! Look at the difference:

Spark1.jpg
Spark2.jpg

I think mine were the original ones from the 90s.
 
It's so nice when it ends up being something simple.

Glad you finally got it and enjoy that ski!
 
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