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Discussion Starter #1
I have a 1996 Tigershark Monte Carlo 900 that will not idle in water. Years ago the jet ski was flipped and the engine compartment was filled with water. The water was flushed from the engine and the ski was run to boil off the rest of the water. Sadly we were unable to take it back on the water before we had to store it for the winter. Come summer it was difficult to start, but it started. We soon found out that while the ski will idle out of water, it will not idle in water. We got it running once and it would run so long as you didn't let off the throttle. Sadly I haven't had much time to solve the issue so it has been sitting for years with some occasional attempts to get it running. But this time I am determined to get it back on the water!

I decided to do a compression test before trying to fix it again to ensure that I wouldn't be wasting my time on a junk engine. The numbers I got where 110, 120, and 100. This was a cold test with possibly not enough power to the starter. Although the numbers aren't great I don't think it should keep the ski from running. The ski is still difficult to start. The ski idles at around 3,000 rpm out of water. I also used fresh fuel whenever trying to run the ski.

The last time that I had it running I noticed that some of the carburetors seemed to be spitting gas back up the intake a little. to me this didn't seem right so I have been looking into carburetor issues. My thought is that may not be getting enough gas due to a faulty or dirty carb, giving enough power to idle out of water, but not enough to turn the impeller once in the water.

This brings me to the main reason I decided to post to this forum. I began disassembling the carburetor and while some screws are somewhat corroded it looks like the jets and float are free of corrosion and in good condition. What I came across is that all of the diaphragms have some wrinkling to them (see attached image). Being from an era of fuel injected engine my knowledge of carburetors is somewhat limited. From what I have read is that a wrinkled diaphragm is bad, but all of the images of wrinkled diaphragms look much different than the ones used in this jet ski (much thicker rubber) and I don't know what the diaphragms should look like/behave. These diaphragms look like they could easily be slightly wrinkled and work fine. Since I'm not confident in whether or not this ski will actually ever run I figured I would check to see if these actually need replacement before I start sinking money into this ski.


Some additional information: Although this ski is old it has had very little runtime. It sat in a warehouse until someone else starting using it and they only used it a few times before they sold it to us. It ran great when we got it, but we just so happened to have flipped it on the first day of use, so we haven't exactly put any runtime on it either. Figured this might help rule out some possible wear and tear issues.


I know this was a lot of text and appreciate anyone who actually bothered to read it all. Primarily I just want to know if the diaphragms are good, but I would also greatly appreciate any suggestions on what may be wrong with the ski. I will gladly answer any additional questions you may have. I don't know how soon I will actually be able to start trying them, but I should be able to start really digging into this soon.
 

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Discussion Starter #2
I was able to find the model number for the carburetor and from what I can find the wrinkling seems pretty normal. The diaphragm still has elasticity and I doubt it has any holes due to its lack of use, but I will check for holes when I do my cleaning.
 

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Carbs are Mikuni bn-i series. There are little passages and a inlet screen that jet plugged up. The diaphragm you are picturing is the regulator diaphragm. It regulates the fuel flow at given throttle positions. AT full throttle it will push down on the needle arm to open the needle all the way.
If it has been sitting for years, you need to rebuild the carbs. When you get the kit, do one carb at a time so you don't get parts mixed up between them. Before removing any mixture screws, carefully count and document how many turns from lightly seated each screw is. It has to be returned to that exact position. There is a high speed and a low speed screw. Do not get them mixed up, and do not under any circumstance use the low speed screw to adjust idle speed. That is what the idle screw is for. The kit might come with a new spring, but just reuse the old one. Do not separate the carb rack. Keep them together. I recommend getting true Mikuni kits for your first time. I also recommend you get a manual for the ski, replace the oil injection lines, and fuel lines (especially the oil injection lines as they get old, stiff, and brittle). If you get a 50cc syringe from a feed store, you can carefully fill the new lines, but try and keep from getting any air bubbles in there.I would also add a tablespoon of oil to each cyl to recoat the walls and rings, and add about 1.25oz per gallon of oil to the first tank of fuel.
I'm hesitant to say those compression numbers are good, and that the bottom end is any good, but only time will tell. There should only be max variance of 10% between cyl's.
Jusy fyi's. Don't crank the engine for more than 10 seconds at a time, and let it rest. It will overheat and burn up the starter. I ususally do about 3 sec. shots until it fires. You can also mix up a small bottle of pre mix to use for priming. Do not run it without water any more than 10 seconds, and then let it cool off for a bit, and if running on the hose, no more than 5 min., and.. Start the engine first, then turn on the hose, turn off hose, couple quick light revs, shut ski down.
 

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Discussion Starter #4
Thanks for all the information. I actually have a manual already (the previous owner gave it to me). My only question is that the manual says to lightly tighten the jets and then back them out one turn. Should I follow the manual or keep them as is? For all I know they could be set wrong already for some reason.

I always make sure that the ski doesn't run long without water, but a maximum of 5 minutes on water is new to me, thanks for that.

I'm aware that the all cylinders should be within 10% of each other. Honestly with all this ski has been through over the past several years I was expecting it to be worse! My main hope is that once it is up and running is that the warm compression is better than the cold (after all, this is how I will be using the ski).

Thanks for your help. I do appreciate the suggestions to help prevent my engine from getting any worse.
 

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They may be slightly off the 1 turn but not by more than 1/8. If theyre any more than that i would set them back to factory.
 

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Discussion Starter #6
So I rebuilt the carburetor and replaced the fuel with fresh fuel. The new issue I seem to be having is that I'm not getting any gas to the carbs. When I reattached the gas lines they were bone dry. After cranking the engine for a few seconds about five times there the lines are still completely dry. How long should it take for the fuel pump to fill these lines and get fuel to the carbs? will the pump even work if the lines are dry? Do I need to fill them?

I also haven't replaced the lines yet as I was hoping to see how the ski ran before I put anymore money into it. The lines don't seem like they have any damage. They do seem a little stiff though, so it could be an issue with the lines, but none of the carbs are getting fuel. Unless a single bad line could throw off the fuel pump I feel it is unlikely that all the lines have completely failed.

Could it be possible that the fuel pump needs to be repaired?

Any insight would be greatly appreciated so I don't have to waste too much time and money chasing every possibility.

FYI, I made sure that the gas knob is turned to the on position.
 

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It is very possible the pump needs to be rebuilt also. I would make sure the pulse line is good and secure, and maybe make sure all the fuel lines are secure. You might try bypassing the fuel selector valve. Could be a blockage there also.
 

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Discussion Starter #8
Thanks for your help. I think that I'm going to start with the pick up lines first. After some research I found that the pick up lines tend to fall apart. There also isn't a ton of gas in the tank so that might be why I am only noticing this problem now. I'm also going to try running on reserve an see if I get gas.
 

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Discussion Starter #9
I checked the pickup lines and they were fine. I rebuilt the fuel pump and was able to get the ski running on the trailer. After letting it idle for awhile and noticed that one of the cylinders seemed to be smoking/steaming. Upon further inspection I noticed that the center cylinder appears to be leaking water from the crankcase gasket. I don't know where the water runs so I'm not sure if this should even be able to leak water. This cylinder overheated in the last time we got it running for a single trip (enough for the cylinder head to brown a little). I figured it was probably tied to a possible lean carb issue, but it looks like the is probably the issue. shortly after spotting the issue the ski began to struggle to idle and then died. Looks like I will likely be rebuilding the top end of this engine. I just hope that the overheating didn't cause any warping.

I had also noticed that when you rev the ski, the PTO carb (and only the PTO carb) spits back some gas and smoke. I wasn't able to tune the carb beyond the initial setting that the book has, so it's possible that this is the issue.

Is there anything you think I should be aware of or that I should check before rebuilding? Is there any underlying issue that may have caused this that could blow the gasket again?

I also have a question about what the crankcase gasket affects. If I am correct the piston head should always be above the crankcase gasket. So the crankcase gasket would not affect compression?
 

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I would do a compression check. Yes, the base gasket can affect compression a small amount, but more so of a lean or hard starting condition. I don't believe water travels down that far on that engine, so I would suspect a leaking exhaust gasket or cracked cyl. Depending on how hot it got, you may be doing a full rebuild as it may have slightly hurt the lower rod bearings, or if water made it's way into the crankcase, it would have rusted the bearings. When you pull the top end, check for any rust at all on the counter weights, smoothness of bearings, and rod thrust clearances.
 

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Discussion Starter #11
Thanks. I will check all of that. I'm just hoping that the cylinders are fine, as I'm sure finding a replacement will be a pain if it is cracked. I also hope that it doesn't need any bottom end work as that is when things begin getting time consuming. I will certainly check to be sure, but I can still turn the engine over by hand fairly easily, which I would think wouldn't be possible if things were rusted on the bottom end.
 

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I think I may have just found my issue. I just remembered that I noticed one of the water lines that is connected to the cylinder heads was leaking the last time we had it running (this was years ago). I noticed the water on the carburetor side of the engine, which is opposite from the line, but I think it was leaking into the channel between the cylinders and I only noticed it on that side because it was easier to see. I don't remember which cylinder was leaking, but I bet that this is the overheating issue. The only thing is this is a small leak. From what I have read about other skis is that a small leak is all it takes to cause overheating. Is this correct?

Also, on the topic of the carburetor spitting back. After doing a little research I think that the reed valves might be the issue. Seems like they are allowing combustion gases to come back through the intake.
 

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Discussion Starter #13
I did another compression test to see make sure that nothing has changed after running it on the trailer before I start buying stuff. oddly enough the PTO cylinder is now up to 124 from 110, the rest are about the same. I did notice though that the MAG and center cylinder built up pressure slower than the PTO cylinder. I decided to jump in and remove some of the heads. The PTO cylinder looked healthy, but had quite a bit of sand in the cooling section. What is the best way to clean sand out of here, and why is it here in the first place? The gaskets on the center cylinder on the other hand had both the inner and outer gasket blown. I'm not sure how I'm getting 116PSI of compression on this cylinder The outer gasket was blown where I saw the water. It must have been dripping down and I only noticed it when it got to the bottom of the cylinder and started boiling. I have already ordered a head gasket set and will be putting them on when I get them.

I didn't check the MAG cylinder yet because I would have to remove the exhaust first. Hopefully it is just a blown head gasket like the rest.
 

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The sand has to be rinsed out. It gets in there from running in to shallow of water. Pwc manuals state do not run in less than 2ft of water, just for that reason of sucking up debris sitting on the bottom. My advise is to pull all the jugs off and rinse them out, and thoroughly rinse the exhaust system.
 

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Discussion Starter #15 (Edited)
While waiting for the head gasket kit to come in I decided to check out the reed valves and found this (see attached image). The reed valve is missing a huge chunk. This is from the PTO cylinder which was spitting back a lot of gas. I checked to make sure that it isn't still stuck in the intake, and it's not. It must have been sucked into the engine. Doesn't look like it damaged the cylinder. What other possibilities are there for damage?
 

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Looks metal. If so, you need to find it. That will cause the prob you are having along with slightly lower compression, hard starting, and low power. Replace all of them with a set of Boysen pro series set.
 

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Sadly I have already ordered steel replacements and they are on the way. I did some research and it seems that most people say that the steel reeds will often get broken up in the crankcase, possibly nick the piston or cylinder wall, then exit out the exhaust. Overall the damage is usually fairly minor from what I have read. As I stated that cylinder seems undamaged. So I either got lucky or most of it is still in the crankcase. Either way I would really rather not pull the engine out and open the crankcase if I don't have to. Not only because it is time consuming but there are also a lot of things that could go wrong, and since I am not that familiar with these engines, I fear something would go wrong.
 

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Been so long i cant remember if they are std spring steel or stainless. Might check with a mag. Might be able to use a small retrieving mag and fish it out.
 

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Discussion Starter #19 (Edited)
The reed was actually still connected and stuck in the cage, so no need to retrieve! I changed the reed valves and head gaskets today. I started it up and it seemed to run a lot better. The carb didn't spit back, no water leaks, and no apparent overheating.

One thing that concerned me though is that while running it on the hose the jet pump seemed to rattle quite a bit. From my research some people seem to think this is normal, others suggest rebuilding the jet pump. Seems almost like it may even be specific to certain skis. Any input to whether or not this is normal for Tigersharks?
 

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Jet pump noise is halfway normal, but should not be overlooked. The bearings are prob. getting worn, and replacing them and the seals is a good idea now before they go out.
 
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