1994 SeaDoo XP Low RPM in Water

[Venom]

Hi All,
I have been working on ATV's and most anything with an engine for many years. I have owned personal Watercraft in the past. Right now i am trying to help a friend with his SeaDoo XP. After much research it seems it is a very common problem.
The XP runs great on the trailer, Around 7K RPM. It runs all the way up until the rev limiter kicks in. On the water it starts right up and pulls hard until 4K RPM and that is where it stays. I have read countless threads about this problem. But, I either found someone had the problem, started trouble shooting, fund the problem ( usually the rectifier ) and they are up and running again. A large portion of what I read.. Someone has the problem, starts troubleshooting and never finds the problem even after they have replaced numerous parts and completed all the troubleshooting. And third lots of threads never showing the outcome or if they ever got it fixed.
I would like this to be the thread that goes from start to finish in diagnosing and repairing the issue.
I have obtained the service manual and started testing components.. The thing I found funny is that at the end of electrical testing procedures it states.. " Even though everything may test ok, that does not mean the part is working, only replacing the part will be the definitive answer" Anyone that would like to chime in feel welcome... Thanks for any help.

 

[Venom]

Please give your advice on tests I should be doing.
Tests and observations done so far:

1. Meter on battery, started XP, took it to 5500 RPM. Results averaged 13.7 volts.
2. Compression Test. Front Cylinder 131, Rear 130
3. Idles at 3000 to 3100 RPM on Trailer. 1500 RPM in water.
4. Cleaned Factory Fuel Filter
5. No Obstructions in exhaust or water lines
6. Took off carbs Disassembled, cleaned, reassembled. ( This step I should repeat and check pop off pressure )

 

[jmartin2178]

This may sound simple, but I had a similar issue with mine and it ended up being a clogged fuel filter. Replaced the fuel filter with a larger one and currently works like a champ.

 

[Venom]

This may sound simple, but I had a similar issue with mine and it ended up being a clogged fuel filter. Replaced the fuel filter with a larger one and currently works like a champ.

Thanks for the response, I will replace the fuel filter today.

 

[Venom]

When people say the exhaust is clogged.. Where does it clog? By the Head?

 

[AKnarrowback]

You should not need to put a larger fuel filter on. Just clean out the stock one under the dash. It's a filter / waterseperator that can be taken apart cleaned and put back together in 30 seconds. It works better than any other in line filter you can put in.

I'm not an electronics expert, but the rectifier problem seems to be an issue with the newer DESS system type machines and not the older machines.

Have you taken the carbs apart and done a thorough cleaning?

A clogged exhaust? There isn't a really tight passage to clog on these machines. I have never heard of a clogged exhaust before. If it started on the trailer then the exhaust is flowing. It's when the exhaust outlet is too far under water that starting these things can take a few extra seconds, but once the water is pushed out they stay running just fine.

When I stand my machine on end I can stall the motor by giving it a quick blip on the throttle that shoots it up and lets it settle back in about half way. If I'm not on the gas when it settles in the exhaust is so far down that the back pressure from the water stalls the motor.

 

[tjones823]

You should not need to put a larger fuel filter on. Just clean out the stock one under the dash. It's a filter / waterseperator that can be taken apart cleaned and put back together in 30 seconds. It works better than any other in line filter you can put in.

I'm not an electronics expert, but the rectifier problem seems to be an issue with the newer DESS system type machines and not the older machines.

Have you taken the carbs apart and done a thorough cleaning?

A clogged exhaust? There isn't a really tight passage to clog on these machines. I have never heard of a clogged exhaust before. If it started on the trailer then the exhaust is flowing. It's when the exhaust outlet is too far under water that starting these things can take a few extra seconds, but once the water is pushed out they stay running just fine.

When I stand my machine on end I can stall the motor by giving it a quick blip on the throttle that shoots it up and lets it settle back in about half way. If I'm not on the gas when it settles in the exhaust is so far down that the back pressure from the water stalls the motor.

I know this sounds stupid but what’s your idle RPMS out of water? I had same issue and my idle rpms out of water were to low so when in water it would bog out

Turned my idle rpms up to 3000-3500 out of water which is about 1500 in water.. no more issues

 

[etemplet]

Did you replace your spark plugs? Did you remove the spark plug caps to determine if the wire is in good condition and the cap is making good contact. Some people clip 1/4" off the wire but be careful that your wire will still reach the spark plug. You're coil could be breaking down under load but to me that possibility is remote.

There are 4 holes in the carburetor barrels that should spray nice streams of cleaner when you test them. (see carb rebuild thread). The 3 smaller holes in the center seem to be the most troublesome.

When you take the ski to the water try pulling the choke out a bit at 4k to determine what is going on. If it runs worse you are getting too much fuel. You could raise the pop-off pressure to the higher range... that leans out the fuel and makes big differences sometimes.

These skis are not easy sometimes.

 

[Venom]

You should not need to put a larger fuel filter on. Just clean out the stock one under the dash. It's a filter / waterseperator that can be taken apart cleaned and put back together in 30 seconds. It works better than any other in line filter you can put in.

I'm not an electronics expert, but the rectifier problem seems to be an issue with the newer DESS system type machines and not the older machines.

Have you taken the carbs apart and done a thorough cleaning?

A clogged exhaust? There isn't a really tight passage to clog on these machines. I have never heard of a clogged exhaust before. If it started on the trailer then the exhaust is flowing. It's when the exhaust outlet is too far under water that starting these things can take a few extra seconds, but once the water is pushed out they stay running just fine.

When I stand my machine on end I can stall the motor by giving it a quick blip on the throttle that shoots it up and lets it settle back in about half way. If I'm not on the gas when it settles in the exhaust is so far down that the back pressure from the water stalls the motor.

Found the factory fuel filter. Took it out and it was remarkably clean, flushed it anyway and put it back in.
I see another filter that looks like it may be on the 2 stroke oil line. I am attaching a photo. I have taken the carbs apart and stuck them in a large Ultrasonic Cleaner.. I rebuilt them and they seem to be working fine. As far as the clogged exhaust I found some more info on that. It appears the blockages occur on the smaller hoses and elbow fittings. I found a blockage in the small hose coming off the head that exits out the rear through a tiny hole just under the tow ring. Blew out the blockage from the head side of the hose. made a slight pop and a little water sprayed out the back. Now it is free and clear. Photos included. I still have many hoses to check for blockages. The service manual states under troubleshooting: Exhaust system restriction can cause lack of acceleration or power. It also states to only replace those elbows with the exact part number because the hole sizes are specific to that engine.
Some state they have cleaned out all those lines and it fixed the problem.
Thanks for your help

 

[Venom]

I know this sounds stupid but what’s your idle RPMS out of water? I had same issue and my idle rpms out of water were to low so when in water it would bog out

Turned my idle rpms up to 3000-3500 out of water which is about 1500 in water.. no more issues

Idles at 3000 to 3100 RPM on Trailer. 1500 RPM in water.
Thanks for the help

 

[Venom]

Did you replace your spark plugs? Did you remove the spark plug caps to determine if the wire is in good condition and the cap is making good contact. Some people clip 1/4" off the wire but be careful that your wire will still reach the spark plug. You're coil could be breaking down under load but to me that possibility is remote.

There are 4 holes in the carburetor barrels that should spray nice streams of cleaner when you test them. (see carb rebuild thread). The 3 smaller holes in the center seem to be the most troublesome.

When you take the ski to the water try pulling the choke out a bit at 4k to determine what is going on. If it runs worse you are getting too much fuel. You could raise the pop-off pressure to the higher range... that leans out the fuel and makes big differences sometimes.

These skis are not easy sometimes.

Although the plugs seem to be working perfectly, I did order new plugs that will be here Saturday. I did inspect the boots and they are very clean inside on both ends. I did clip back the Spark plug wires and the wires looked great. I have thought about the coil.... I have seen coils do exactly what you are saying on ATV's. Since I saw no one that found that to be the problem I have kind of put that on the back burner for replacement.
Thank you for the carb info.. I will look for the carb rebuild thread. I have rebuilt the carbs and it runs the same but it is always possible I missed something.
I will try pulling on the choke in the water to see the difference
Thanks for the help

 

[Venom]

After working on lots of vehicles I find the SeaDoo XP Service manual really lacking in detail in many areas.
I appreciate all the help..

 

[etemplet]

Exhaust system blockage confused me for a long time till I removed the large exhaust hose from my 1996 GTX 787. The hose was internally blistered and I could see where exhaust gasses might blow up the blisters like a ballon further blocking/restricting the flow of the exhaust.

For your ski those smaller hoses are for cooling water. The one that goes out the back under the tow ring is the tattle tale. It lets you know you are getting water flow to the head. All good checks though, make sure everything is clear. Good Luck.

 

[j.harris]

As for the carb rebuild did you check pop off pressure and that the needle and seats seal?

 

[Venom]

As for the carb rebuild did you check pop off pressure and that the needle and seats seal?

Hahaha, I was just reading that in the Carb rebuild thread when I got notification of this message.. guess the carbs are coming back off.
Thanks for the help

 

[tjones823]

Found the factory fuel filter. Took it out and it was remarkably clean, flushed it anyway and put it back in.
I see another filter that looks like it may be on the 2 stroke oil line. I am attaching a photo. I have taken the carbs apart and stuck them in a large Ultrasonic Cleaner.. I rebuilt them and they seem to be working fine. As far as the clogged exhaust I found some more info on that. It appears the blockages occur on the smaller hoses and elbow fittings. I found a blockage in the small hose coming off the head that exits out the rear through a tiny hole just under the tow ring. Blew out the blockage from the head side of the hose. made a slight pop and a little water sprayed out the back. Now it is free and clear. Photos included. I still have many hoses to check for blockages. The service manual states under troubleshooting: Exhaust system restriction can cause lack of acceleration or power. It also states to only replace those elbows with the exact part number because the hole sizes are specific to that engine.
Some state they have cleaned out all those lines and it fixed the problem.
Thanks for your help

Change all those lines! And that filter!

Also make sure the pisser in the back is pissing or those lines are clogged to.. just replace them all

 

[MikunisFromHell]

inspect the plugs. Black, fouled, wet = rich. Dry, grey= lean. You want chocolaty brown.