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RSRBOB, Technician
Category: Boat
Satisfied Customers: 1078
Experience:  Former Yamaha Factory Service Rep, Dlr Line Tech, Serv Mgr, G/M
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I have a 2004 Yamaha XLT1200. I'm having an issue where the

Customer Question

I have a 2004 Yamaha XLT1200. I'm having an issue where the jet ski wont go over about 15 mph and dies if you quickly pull the throttle.
I have replaced all the seals in the carbs, replaced all the fuel lines from the tank to the carb, new fuel filter and cleaned the selector switch. It starts okay if not cold, otherwise it seems it takes a while to start the first time. Once its started it will run idle okay but if you give it gas it bogs down and dies. If you easy the rpms up it wont go over about 15 mphs.
Submitted: 2 years ago.
Category: Boat
Customer: replied 2 years ago.
To add, I've also removed the CAT and replaced with a Dplate. I also removed the oil pump and went to premix.
Expert:  RSRBOB replied 2 years ago.

Hi and thank you for your question.

The very first thing we need to do is check the compression. This can create a whole hose of problems, some of which are like what you are experiencing.

Check all 3 cylinders, and keep the other 2 spark plugs installed in the engine as you test each cylinder.

Let me know what you get for compression and we can go from there.


Customer: replied 2 years ago.
RSROR,I have 110 across all 3 cylinders.-Jeff
Expert:  RSRBOB replied 2 years ago.


The compression is low, but not alarmingly low and it is consistent, so we will leave that alone.

You said you replaced all the seals and gaskets in the carbs. Did you see any damage while they were apart? Also, where do you have your low speed and high speed screws set to? What color are the spark plugs when you take them out? Did you do anything with the needles and seats, or did you adjust the float arms? Did you take the high speed and low speed jets out to make sure they were clean when you had the carbs apart?

This sounds like a fuel issue, considering the compression is consistent. When it only goes 15 mph, is the power just flat and not wanting to rev any higher or is it sputtering? How many RPM's is 15MPH?



Customer: replied 2 years ago.
RSRBOB,I'm going to try and answer this in order.1. Damage while they were apart - Nothing that I could tell, not an expert by any means but I did have to use a brush to remove some residue from the old paper gaskets. There is a lot of corrosion to the outside of the carbs. So much so that the idle adjustment screw holding bracket had broke off, so I cant re attach the idle adjustment screw. I sort of bypassed that by adjusting the idle on the throttle cable directly.2. High and Low Speed Screw Settings: I didnt mess with them, didnt remove them. Honestly was to intimidated to do it.3. Spark plugs are new, but when I remove them they seem clean. I did notice they seem like they get cleaner the closer to the front of the jet ski I go. Meaning the 1st cylinder closet to the rear of the jet ski seems dirtier than the last one closest to the front.4. I did remove the needles but not the seats. I just looked to see if they had any damage and they didnt. Didn't have any real signs of wear.5. In terms of power it is about 5000 RPM at 15 mph. But you cant just pull the throttle and get to that. You kind of have to baby it up to that but thats fully pulling the trottle at the point you get 5000 RPM. Not sputtering really just not wanting to rev hire. If you pull the trottle quickly it bogs down and dies. Sometimes you cant even get it to 5000 RPM, sometimes you can barely get above just idle speed.6. One thing I did observe that I dont understand when replacing the fuel lines I had a really hard time priming the lines. Finally out of frustration I bought a 2 foot section of clear fuel line. I removed the fuel line going into the carbs from the fuel filter and basically used two 1/4 nipples to connect this clear fuel line to the fuel filter and then to the carbs fuel feed line. I saw large amounts of bubbles in the fuel. Which leads me to believe i'm sucking air somewhere above the carbs in the fuel system. At that point I removed the fuel selector and replaced all the fuel lines from the selector to the tank. Still same problem you can see bubbles in the fuel. Sometimes even big gaps of air between the fuel. The only thing I have messed with is the vent line from the gas tank. It has a check valve on it that I think is meant to keep gas from going out the vent if the ski turns over. Is it possible that I have something wrong in that vent line? I'm sure the carbs could be cleaned better than I did them but what I cant figure out is where and why that air is in the fuel lines.
Expert:  RSRBOB replied 2 years ago.

Hi and thank you for the additional information. Highest praises to you for your clear concise method of replying. It is refreshing to get a reply such as yours. Sadly it is the exception not the ruel. :)

This may or may not help me, but what transpired that led you to working on the carbs? (No easy task I might add, how about that exhaust pipe?)

Now, I do have one further question, and the observation about air in the lines raises it. Did you inspect the fuel pump side of the carb? That is the side of the carb with the large rectangular aluminum block with the 4 screws, not the flat diamond shaped steel plate. The check valves in the fuel pump have been known to crease and no longer seal. I am also curious if you replaced the fuel lines that are inside the fuel tank? It does sound like you are getting air from somewhere. At this point, those seem to be the highest probability for creating the symptoms you are experiencing.


Customer: replied 2 years ago.
RSRBOB,I got the jet ski with a busted engine. Previous owners had thrown a rod through the crank case. I got lucky enough to find this motor in the area from a guy who was parting out his jet ski for unknown reasons. The engine had good compression so I thought what the heck. At this point I had nothing but an empty hull so I figured i may as well clean the carbs because they had been sitting up for about 3 years. I did work on the fuel pump side. I replaced all the gaskets and the two clear plastic check valves which I assume I put on correctly. I didn't replace anything inside the tank. All i did was replace the fuel lines up to the nipple on the tank. The carb rebuild kits that I bought didn't indicate which direction those check valves had to go so I assume they were bidirectional.I have a second jet ski, an XLT 800, that I havent started working on yet that has the same symptons. It however has a good engine but it sat up for a few years as well.It is possible to get air leaks from the fuel selectors?As far as the carbs are concerned...i can pull them back off and reinspect those check valves and even send you some pictures. I just hate to have to remove that complete pain in the...exhaust.
Customer: replied 2 years ago.
Also the exhaust pipe, i was told that the cat converters in these could cause problems as they broke down. This one was so bad it feel apart in my hands. Some internet searching led me to the Dplate modification.
Expert:  RSRBOB replied 2 years ago.

Thank you for the additional information.

The round clear plastic pieces are the check valves I was referring to. They are in fact directional, BUT, I have serious doubts that it would affect the way the ski performs. There is a blue line on each check valve that is supposed to be installed away from the aluminum block. I have looked for a difference of one side vs. the other side and cannot for the life of me find a difference, other than the blue line. I don't think going back into the carbs is indicated at this point. I am still impressed you could get it done and are even remotely volunteering to do it again.

In thinking deeper about this and based on the information that you never heard this engine run correctly, I have to ask if you checked the reed valves closely when you had the carbs off? If the engine were to get water in it below the piston when it comes down it forces it back out the intake and can break the reed valves. Just another thing to think about.

The idea I had about the fuel lines in the tank was if there is a crack or hole in them that would allow them to get air in the lines. It sounds like you replaced all the lines from the top of the tank to the carbs.

If you are re-using the electrics that came with the engine, perhaps we need to check them out to make sure we aren't dropping a cylinder as we try to rev it up. To do this, you will need cooling water. Either run it on the flush kit, leave it tied to the trailer and back it in the water so the jet is under water, or tie it to a dock, unless you are on a very un=busy body of water where you can ride it around a look at a timing light while underway. You will need an automotive type inductive timing light to check the ignition. Primarily we want to see if we are loosing spark to a cylinder as it revs up. Secondarily we would like to see the timing advance as it revs. You are going to need to be able to see the coupler to determine that. Which constitutes removing the plastic shield over the coupler, putting the front cylinder at top dead center, and making a mark with a magic marker on the top of the coupler, at 12:00. Start the ski and observe where the mark that you made is, then rev it and see if it moves (advancing) from there as you rev the engine.

One other thing to think about would be if the power valves are stuck down. At 5000 RPMs you should be able to see the pulley with the cables on it move along with the shaft that connects all the cylinders together. It is not unheard of for them to get stuck from being carboned up, and quite possibly from sitting too.

One last question I have would be did you take a look at the throttle plates and did they appear to be at the exact same opening at rest. This is carb sync and can negatively affect an engine's ability to rev.

Give those things a try and see where we are at.