09-24-2012, 10:58 PM #1
The be all end all “My STX 12f or 15f or Ultra LX is not running right” Thread
Hello and welcome to the forum, if you are reading this I am able to assume that unfortunately your ski is not running as well as it should be (or at all). Let me begin by saying DON’T PANIC, there skis are just like any other mechanical device and as such do have problems. Fortunately these skis can take a severe amount of abuse (within reason) without major failure. I have personally run my 15f with a majorly rich air fuel ratio, sunk it 2 times, and run with more than 50 degrees of timing at idle. I can’t recommend this nor did I do this on purpose but when building a ski that is in uncharted waters you find things out that you shouldn’t.
This guide as you can tell by the title will cover the NON-SUPERCHARGED Kawasaki engines that power the STX models as well as the Ultra LX. Before beginning any of the diagnostics make sure that the battery is fully charged and that you have a fire extinguisher nearby. If the battery is charged but the motor will not turn over ensure that the motor is not hydrolocked (full of water) or that the jet pump bearings or impeller are not seized. If either is the case do not attempt to crank the motor any longer as damage will result. If the jet pump is locked up and you remove it DO NOT attempt to start the motor, this will damage the drive shaft support bearing and could damage the hull.
My engine won’t start:
Bad or old gas
Gas will not last forever, this is not leftist propaganda it’s the truth. Modern fuel contains ethanol and in some cases can contain up to 20%. Ethanol wicks water in and as basic chemistry teaches us water is not combustible under normal circumstances. Get a siphon out and suck the old gas out and put fresh gas in. Give it another shot on starting, if it doesn’t start move on to the next step.
Bad spark plugs
The spark plugs may still look okay but typically this is the easiest fix and fairly cheap as well, use the spark plug in the tool in in the tool kit under the seat, the top is 17mm and the wrench is also in the tool kit. Remove the plugs and replace them with P/N NGKCR9EK or CR9EIX. While you have the spark plugs out check the compression, you will need a 10mm adapter to test with. To properly check compression you need to open the throttle fully and crank the engine over for a few seconds until the gauge stops rising (it will still move but the reading will stabilize after a few rotations) As per the Kawasaki Manual, the compression for a 15f or Ultra LX should be between 172 and 260 P.S.I. What you should be looking for though is consistency between the cylinders. If you have any cylinder which is lower than the rest by a large margin or is 0 bigger problems lie beneath and you should begin more in depth troubleshooting. When you reinstall the spark plugs be sure to use ANTI-SEIZE on the spark plug threads and install with a TQ wrench and Torque to 113 In-LBS (This is important because the Kawasaki spark plug threads are fairly small and can either strip or break the plug when removing it or installing. If you feel resistance while trying to remove the plugs, stop, have a beer or beverage of your choice and spray some penetrating solution on the plug and let it sit then come back and try again) If replacing the spark plugs doesn’t get the engine to start move to the next step.
Low Or No Fuel pressure
If your engine is not getting enough fuel it will not run properly or at all, on the 12f, 15f, and Ultra LX the Fuel pressure should be 43 P.S.I. at idle or just after cranking. If the fuel pressure is low there are a few different potential causes. Just after cranking the motor over you should hear a whirring sound. If you do not hear the sound remove the fuel pump housing from the fuel tank, and check for rust on the fuel pump. If there was ever water in the fuel it could have damaged the fuel pump resulting in lower fuel pressure. You can attempt to turn the fuel pump over on the bench to verify but it is typically easy to see if the pump is dead. If you hear the pump working check the pressure just off the send line of the fuel pump. Then check the fuel filter for flow, if it is clogged it will need to be replaced. The third possible cause is a faulty fuel pressure regulator. This is on the return side of the fuel pump assembly and is a small box shaped item secured by 2 screws on the fuel pump can. This should hold up 43 psi if pressurized with an air compressor, if It doesn’t it will need to be repaired by adding some spring tension or replaced with an aftermarket external regulator. If the ski does not start at this point move on to the next step
Faulty fuel injector
While this is a rare occurrence it is possible for the injectors to degrade or become clogged, if you think that an injector may be plugged, remove the ignition coils and crank the engine over for a few seconds then remove the spark plugs, if any of them are dry the injectors are not working either due to electronic issues such as faulty wiring or a dead injector, this can be verified by removing the faulty injector and swapping it to a different cylinder. If all of the injectors are functioning properly move onto the next step.
Faulty ignition coils
The Kawasaki Ignition system is driven by what is called a waste spark system which uses 2 ignition coils to fire the 4 cylinders. The Kawasaki coils are pretty reliable but if you have reached this point this will not be comforting. Check the ignition coils by removing the spark plugs from the head and grounding them to the engine with the coils connected. (It is also a good idea to remove the fuel injector plugs as well while doing this) Then crank the engine over and check each of the 4 spark plugs for sparks. If you don’t see a spark make sure that the spark plug is grounded and if it is replace the coil or plug wire. If this doesn’t fix it move onto the next step.
Unplugged wiring, damaged connectors, damaged sensors or wrath of God.
At this point if the ski is not running you need to evaluate whether or not you should take the ski to the dealership. Before you give up and part out your ski, it is worth picking up a multimeter and testing the sensors resistance values, the cam position (400-460 ohms), crank position (408-612 ohms), and (old style non brass) temperature sensors (oil and water temp 293k ohms at 68 degrees f and 13.2k ohms at 212 degrees f) can all be tested (at least partially) with a standard multimeter. It is also worth really going through the wiring harness and looking for unplugged connections, without all the sensors plugged in nothing will happen. Throttle position, map sensor, and vehicle down sensor all require special tools to test but if you think these are problematic take it to the dealer and specifically ask for them to be tested.
Next we will go through the possible causes for poor running at idle.
Last edited by smokeysevin; 01-14-2014 at 10:11 PM.
09-24-2012, 10:59 PM #2
In part one of this series we went through the various causes of why your naturally aspirated Kawasaki engine was not starting, in this part we will go through common causes for less than optimal running at or around idle, if you are at this point I am assuming that your ski will start, if not please go back to the post above and read through it and follow the steps outlined then return to this post once you have your ski running. If the ski is running but not optimally please go through the first post anyways as this will likely clear up any problems you have. If it doesn’t return to this point and follow the guide.
If you can get the ski to run and ride but it dies when coming off throttle or it will not idle smoothly, there could be a few problems.
Idle Control Valve not functional.
Kawasaki uses a stepper motor idle control valve to regulate the idle and to operate the Kawasaki Smart Steering or KSS. When you crank the engine over while trying to start the engine then let off without the engine running or when you shut the engine off after running there will be a clicking or ratcheting noise that comes from the top of the throttle body if you do not hear this noise check to see that the 3 wire plug is connected, if you still do not hear this noise you have 2 options to allow your ski to idle. First, you can replace the idle control valve with a new one from Kawasaki, this will retain your KSS and will regulate the idle as per factory settings. If replacement is not an option it is not the end of the world, you can tighten the idle screw on the throttle body to open the throttle slightly and allow more air past the throttle blade at idle, this works for some people but you will need to keep in mind that the idle will be higher and outside of the ecu’s control. You can either remove the stock idle valve and replace it with a plate or leave the valve attached.
See post 1
Low fuel pressure
See post 1
Worn spark plugs
See post 1
Burned or leaky exhaust
Kawasaki uses a waterbox for sound suppression and exhaust gas temperature control. The Kawasaki skis have a few variations between them but the principle is the same, the ski has a large aluminum cylinder connected to the end of the exhaust manifold by a blue silicone rubber connector. Under this connector are 2 sealing rings similar to piston rings. These rings are fitted into 2 grooves which when the waterbox is slid over compress and seal the exhaust gasses in. There are 3 potential problems here, first is corrosion, if the ski was not maintained and was run in a salt water environment the salt can eat away at the aluminum and allow the exhaust to escape from the intended path. Secondly the rings could have been installed incorrectly and not seal to the waterbox. Thirdly the hoses connecting the exhaust could be burned and leaking exhaust, if you have burned exhaust hoses this is a symptom of a larger problem such as insufficient cooling due to a plugged line or faulty pump and needs to be addressed immediately. Typically a leaky exhaust will result in the ski running fine for some time and then either stalling without restarting until the seat is removed and the engine is able to get fresh air or by the loss of performance once the engine has been running for a while. If any of the hoses have leaks be sure to replace them and check the cooling system for obstructions or cracks in the hoses. Even if you have an aftermarket bilge pump it will not keep up with the 2.5 inch hole in your hull if your exhaust coupler blows.
If the idle on your ski is inconsistent and fluctuates when moving the handlebars be sure to check for any hangs on the throttle cable, with the factory idle control system if the ski is under load and the handlebars turned the engine will blip the throttle once released to enable the steering to function after the throttle has been released. In cases where the throttle cable is pinched or too tight the KSS will activate even if you don’t want it to, be sure that there is a small amount of free play in the throttle cable and that it does not hang or pull the throttle when the handlebars are turned.
That covers the ski operating while coming down to idle or at idle, next we will cover the ski operating across the rest of the RPM range.
Last edited by smokeysevin; 10-03-2012 at 07:32 PM.
09-24-2012, 10:59 PM #3
In part 2 of the series “Help my Kawasaki runs like a Yamaha or Seadoo!” we talked about why the engine of your ski does not run well at idle. In part 3 we will make sure that your ski runs well all the way up to the rev limit. As in previous sections please begin with the first post and check through the things I have listed as in many cases this will solve the problem. 9 times out of 10 the solution is a simple one and usually a cheap one.
"My ski is only running XX mph and I am less than happy!" common causes for less than optimal performance
See post 1
Low fuel pressure
See post 1
Worn spark plugs
See post 1
Burned or leaky exhaust
See post 2
Damaged pump bearings, impeller, or pump housing.
In the jet pump on the 12f, 15f, and Ultra lx there are bearings that hold the pump shaft in place and allow it to rotate. There are 3 seals that prevent water from entering and damaging the pump bearings, There is one at the front of the pump, one inside the black plastic part of the pump cone and one in the metal part of the pump cone, if installed incorrectly these can allow water into the pump and bearings which allows rust which makes bearings less easy to spin. To check you need to unclip the reverse bucket from the cable, you push the collar on the cable back towards the front of the ski then slide it off the ball mount on the reverse bucket. Then you can remove the 2 bolts that hold the reverse bucket to its mount, this will allow you to access the steering nozzle and exit nozzle on the pump. You will need to remove the bolt that holds the steering cable on (10mm) and then remove the 4 bolts that attach the exit nozzle to the pump (12mm) this will allow you to access the 3 bolts that hold the pump cone on (10mm) remove the three bolts and remove the cone, twist and pull. Once the cone is removed check for water intrusion in the pump. If you see signs of water in the pump remove the 2 hoses on top of the pump by loosening the hose clamps and pulling. Then remove the 4 bolts that attach the pump to the pump shoe (14mm). Before you pull and yank on the pump you need to climb under the ski and remove the 2 allen head bolts from the center of the ride plate (5mm). Now you can pull on the pump and further inspect it for signs of water entry. Once removed spin the propeller, there should not be any real resistance while trying to turn the prop, if there is it could be a bad bearing or a damaged pump liner or impeller. If you think it is the liner, the impeller should drag in the same spot on all three blades. If you think it is the impeller it will usually drag one blade across the entire pump. If it is the liner the entire pump housing should be replaced as the liners are not easily serviced like a Yamaha or seadoo pump. If it is the impeller it is usually cheaper to replace the impeller with an aftermarket one or send it out to be repaired. If you see damaged blades on the impeller you may be able to file them out if they are small nics, if they are large replace or have professionally repaired.
In part 4 we will talk about other common issues and how to find, prevent, or fix them.
Last edited by smokeysevin; 10-03-2012 at 07:31 PM.
09-24-2012, 11:00 PM #4
If you have read this far hopefully your ski is running properly and you are ready to hit the water. Before you do there are a few other things that you should check to make sure that this ride is a happy one and not the start of more problems.
If you are having any issues with water in the hull or the engine overheating or nothing coming out of the cooling outlet (pisser) on the right side of the hull the hoses are the place to start checking.
BEFORE YOU START MAKE SURE THAT YOU CHECK ALL HOSE CLAMPS FOR TIGHTNESS AS WITH LOOSE HOSES YOU WILL NOT HAVE WATER SUPPLIED TO THE ENGINE WHICH IS NOT GOOD
Kawasaki uses a manifold on the top of the pump to supply cooling water to the engine and exhaust. This manifold takes the pressure from the impeller and pump and uses it to feed the engine. Because this manifold is fed by lake water it is subject to debris being pushed through which means that the hoses can become blocked. Check the hoses for blockages or debris, remove the manifold from the top of the pump by loosening the 2 hose clamps and pulling them off. Now remove the 2 bolts (10mm) from the top of the pump that hold the manifold on and check for obstructions, it helps to put a small squirt of RTV or silicone sealant on the o-ring to keep it in place when putting the manifold back on.
If you don't find anything in there but are still having issues go through each of the hoses and check for blockages. On the early model 12f and 15f there was another cooling manifold underneath the intake manifold on the right side of the motor that was prone to corrosion and led to 2 problems, overheating due to blockages or large amounts of water filling the hull. There is a newer part that replaces the old one on the 12f and 15f and has a much more corrosion resistant brass fitting.
The other part that commonly causes problems is the output shaft cover on the back of the engine. While this part does not cause problems under normal circumstances, if left in salt water or poorly flushed it will corrode, plug, or leak.
If the ski had not been flushed properly or run in shallow sandy water there is a good chance that the brass fittings have some debris in them restricting water flow, if you have checked the hoses and pump but still have overheating problems this is a good thing to check.
NOW THAT YOU HAVE FINISHED MAKE SURE THAT YOU CHECK ALL HOSE CLAMPS FOR TIGHTNESS AS WITH LOOSE HOSES YOU WILL NOT HAVE WATER SUPPLIED TO THE ENGINE WHICH IS NOT GOOD
Seized Spark Plugs
to remove use the spark plug in the tool in in the tool kit under the seat, the top is 17mm and the wrench is also in the tool kit. Remove the plugs and replace them with P/N NGKCR9EK or CR9EIX. When you reinstall the spark plugs be sure to use ANTI-SEIZE on the spark plug threads and install with a TQ wrench and Torque to 113 In-LBS (This is important because the Kawasaki spark plug threads are fairly small and can either strip or break the plug when removing it or installing. If you feel resistance while trying to remove the plugs, stop, have a beer or beverage of your choice and spray some penetrating solution on the plug and let it sit then come back and try again) If you snap the plug off in the head you have to remove the head to get the plug out so go slowly.
Last edited by smokeysevin; 10-08-2012 at 04:52 PM.
10-13-2012, 10:29 PM #5
- Join Date
- Jul 2011
- Cayman Islands
Don't forget what took me forever to figure out "low compression".
Possiblities seized piston rings, valves sticking and or Worn/ damaged thrust washer/spacer on crankshaft which will eat into crankcase and cause low compression.
Possible cause for worn damaged thrust washer/spacer is a blown jet pump which causes a huge amount of thrust on crank and damages the washer. This a common problem with Kawi skis from what i'm told.
Sorry just adding my experience.
04-14-2013, 01:11 PM #6
It has been brought to my attention that there was an issue with the ECU on certain model STX-12Fs, the ECU has a slightly different ECU tune that runs differently. *Everything that follows this is as I have been informed, due to the nature of ECUs and the different environments in which we are fortunate enough to ride in this is not a blanket statement on which is good and which is not, furthermore this is not to say that you WILL have a failure if your ecu is one of the following or you will be safe with one of the others, I am simply passing along the information I have been given in the hope that I can offer some help in diagnosis.*
That being said there serial numbers on the STX-12F ECUs are as follows
36 (reported 2 cracked pistons under normal operating conditions by fellow member)
32 (current number)
28 (early model ECU)
Any time the engine is opened there is the possibility for the cam timing to be set improperly during reassembly, it is fairly simple to check for this, first remove the spark plug boots from the head. Then remove the emissions tubes from the left side of the engine, then remove the crankcase breather tube from the rear of the valve cover. Now you can remove the oil drainback tube from the front of the engine. Then you can remove the 10mm bolts that hold the valve cover down. It helps to have either an inspection mirror or a cell phone camera to see what position the cam marks are in. Now you need to set the number one cylinder at top dead center (TDC). The proper way to do this is with a TDC finder but it can also be accomplished with a coat hanger or long screw driver in the spark plug hole. In this case it is important to be CLOSE not exact we are not degreeing the cams just verifying their proper location. What we will do in this case is turn the engine over by hand until the screw driver or hanger reaches the highest point, this is a good indication of TDC. To turn the engine by hand the coupler cover must be removed. It is held in place at the back of the engine by 2 10mm bolts.
Check that the cam marks match up with the picture below.
Hot Start Issue
There have been many cases where the ski can become hard to start after riding for a while. These case happen under a variety of circumstances, water conditions, temperature conditions, fuel conditions, and even different age skis. One fix that seems to help most people is out replacing the engine oil temperature sensor located in the oil pan at the front of the engine, and the water temperature sensor located in the exhaust manifold of the ski near the number 2 and 3 cylinders. These sensors have a superseded part number that helps prevent the issue. The new part number is as follows
If you order the sensor be sure to check the number on the kawasaki bag when you receive it as I have been informed that certain part retailers may still have old stock.
When reinstalling the sensors it is important to refill the sensor cavities with a liquid that conducts heat, motor oil will work as will silicone oil. If performing the swap with the engine in the hull you may substitute the oil for silicone dielectric grease or marine grease. Be sure to fill the cavity enough to allow the sensor to receive the transmitted heat.
After installing the new sensors be sure to connect them to the factory plugs and then secure the wires with zipties away from anything that moves or gets very hot.
If you get a TEMP alarm after installing the new sensors remove them and add more oil or grease.
Last edited by smokeysevin; 05-14-2013 at 09:06 PM.
04-28-2013, 08:04 PM #7
Great post for those that own or are looking for a 12F or 15F. I am a bit confused about the ECU's on the 12F. You don't seem to specify which years to stay away from. If I found a good deal on a 12F when I am looking for a 15F, I would be tempted to purchase it but not if the ECU's can cause catastrophic failure.
04-28-2013, 08:55 PM #8
They are not year based, you should just check the number on the ecu itself. That being said none of it is a definitive you should avoid, or a I need this one. It's just guideline.
05-12-2013, 05:29 AM #9
This has helped me a couple of times in diagnosing problems. Great thread!!! The new problem with my ski is pretty obvious though.
Now to get me one of those silicone exhaust couplers to replace the one that burst. Ski kept bogging down and I was 160 miles from home. Had to ride with the seat partially open.
05-12-2013, 09:45 AM #10
I ordered a high temp silicone replacement (hts brand)
Edit: I measured the pipe today and it's 3.1 inches so you should order a 3 inch coupler hose.
Last edited by smokeysevin; 05-14-2013 at 11:11 PM.
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