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  1. #1

    We have not set fire to it......YET!!

    99 STX 1100 triple carb Kiehin model.

    Hi new to the forum and jet ski's, we really need some help with the motor, I will give as much info as possible to save to and fro with questions, sorry for long post but it all is relevant, many many thanks in advance.

    A friend has purchased the above ski, he has zero knowledge about them as did I at the time. It has been running fine for many months with only poor cold starting being anything of note, once started though it used to run great, top speed 80 plus km and always seemed OK until late last year.

    My friend was out with his wife when all of a sudden it lost power, he nursed it back to the shore noting that he had used a lot of fuel, turning to reserve did nothing (we later found out the cables were broke and it was 'on' all the time and reserve was not available), when safely on land he lifted the seat to find the used fuel was actually in the hull!

    After returning home he cleaned it all up and then tried running it, fuel was leaking somewhere so he called me up....god I wished he had not.

    I am a car mechanic buy trade so I think it should be pretty straightforward.....yeh right, I put a mirror under the carbs and the centre one was leaking fuel as was the rearmost one. I removed the carbs and after dismantling I found two worn diaphragms and the rubber 'nose' on one of the needle valves was broken off and lying in the fuel chamber. So we ordered three sets of needles and diaphragm kits and I rebuilt the carbs, I also put new diapragms in the fuel pump.

    I did not alter any of the carb settings i.e. the mixture screws, the diapragms that control the venturis are all good.

    After fitting the engine was difficult to start, once it did though it revved great but the idle was poor and it kept cutting out, after cutting out it was very difficult to start again. Eventually I got started and after managing to alter the carb idle mixture screws (stupid design for access) and it stayed running at around 2000 rpm on the hose but the engine was popping and banging, at times if you revved it the revs would rise but NOT come back down, the throttle was not stuck open, at one pointed it revved to the point we were worried and pulled the stop cord AND THE ENGINE STAYED RUNNING!

    Despite being on the hose (we understand engine on/hose on - hose off then engine off etc) the engine was very very hot, we have never felt it being this hot before and you could even smell it was hot, is there a time limit on the hose?. The hose pressure was good, the water was coming out of the ski exhaust, the small hole above the thrust impeller and also out of the 'vent' at the right hand front side of the ski.

    The fuel (all fresh) seems to be flowing well, the fuel filter on the side of the hull is new and full of fuel, all new spark plugs, fuel filter line to IN on pump, pipe from crankcase to 'infinity' symbol and return line connected to the uppermost connection on the carbs. I have put new cables to the fuel tank and have checked we have flow from both and when OFF fuel is indeed off.

    I have downloaded different manuals but the best I can get is for the ZXi and not the STX, the carbs are similar but they have a max speed screw and the ones we have do not.

    In a nutshell it is running like a bag of spanners, stinking hot, shit starting, the carbs seem to be unresponsive to the idle screws despite the revs being pulled right down, and to get it to start we have to pull the choke control right out. From a car mechanics point of view the hot running/difficult starting seems to be indicating a weak mixture? Current plans based on what I have read thus far, I am going to make some new inlet manifold gaskets, remove the fuel chambers and check the needle valves are opening/closing, I am thinking about checking the reed valves but cannot see the point if they have not been disturbed? Incidently there are no more fuel leaks, whilst on the hose we have a very small trickle of water coming from the back of the ski trickling forwards as the ski is on trailer facing downhill but all good on the oil and fuel side.

    Sorry for the long first post but we are getting desperate.....jerrican and matches at the ready.

    Many thanks in advance guys and girls.

    regards

    Dave


  2. #2
    Pain is fear leaving your body.... rlovebk's Avatar
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    The runaway engine happens when there is a lean condition usually caused by an air leak somewhere. Fuel lines or more than likely carbs intake did not seal well. You can use choke to kill it most times. You will want to address this right away.
    Add a primer, for starts if this has Kiehins anyways. Many 99 STX came with CV carbs which are a pain and you cannot really run primers in these as butterflys work for mix.

    I would go thru entire fuel system again from tank to engine. Replace all fuel lines if needed, check pick-ups and returns in tank and all fittings/filters, etc. Our fuel here eats up diaphrams and seals. Don't know if yours does. You are lucky. That ski is a bomb with fuel in it like that. Very dangerous.

  3. #3
    steve45's Avatar
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    Yes, probably an air leak. Still, there's a possibility that the kill switch was malfunctioning. If you yank the plug wires off and it continues to run (now that's freaky!), you know it's running lean and a hot spot in the combustion chamber is causing ignition. In this case, the easiest way to kill it is wide open throttle.

    I've put primers on several of these engines. There is a balance tube between the carbs. I drilled & tapped holes for the spray nozzles in the elbows on each end of the tube. DO NOT remove the chokes on the CV carbs! They are required for proper fuel metering. Also, run the STOCK flame arrestors!

  4. #4
    Hi and thanks for the replies, 88 views and two replies, like me and my friend it seems that the knowledge base is quite thin on this model.

    rlovebk:

    We are in Spain, interesting the diapragms did seem flimsy, they are all new now, you are right they are CV carbs. The running on seemed to be as mentioned a hot spot, I will make new gaskets tommorow before refitting the carbs. I did not pull the reeds as getting spares here is difficult. I guess if they were working before the fuel leak then they should be ok? I did not pull the unit out of the tank as whenever the fuel lines were disconnected the fuel poured out readily, I also blew down the return line to pressurise the tank. fuel poured out of the fuel line with the fuel switch in the ON and the RESERVE position, this leads me to believe they are clear. I have change the fuel filter in the hull as a 'just in case' measure, the small filters in the needle valves were also clean and strip down.

    Steve45:

    I have seen this primer modification mentioned quite a lot, can I assume it is not something done for an initial fuel refill after stripping but in fact used for perhaps the first start of the day? I also noted that when the choke is pulled out the flaps close ok, so how can the engine actually start with no air? The butterflies on typical car engines will still pull open slightly when the engine is cranking, I assume the air comes ffrom whatever is in the crankcase? When it run away after pulling the kill switch having done a lot of work on turbo diesel engines I thought it was running on the engine oil, I blocked the carbs and that sorted it out. We checked the kill switch over and over and it seemed to work ok so guess it was a hot spot. I have not removed the chokes or the flame arrestors. How the hell can you adjust the idle mixture with the carbs on, the screws are in a very difficult position to access?

    Thank you both for your replies, I will not be working on the ski until Tuesday morning, this might allow anyone else with any ideas to chirp in.

    Thanks again

    Dave

  5. #5
    steve45's Avatar
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    Yes, the primers are typically needed for the first start of the day.

    Air can get past the choke plates, but if you keep the choke on all the way, it will flood the engine. After the engine starts, you partially open the choke until it's pumping adequate fuel to keep it running.

    The carbs have to come off to adjust the idle mixture (along with the flame arrestors). It's a pain in the butt!

  6. #6
    Quote Originally Posted by steve45 View Post
    Yes, the primers are typically needed for the first start of the day.

    Air can get past the choke plates, but if you keep the choke on all the way, it will flood the engine. After the engine starts, you partially open the choke until it's pumping adequate fuel to keep it running.

    The carbs have to come off to adjust the idle mixture (along with the flame arrestors). It's a pain in the butt!
    Hi Steve, I am so accustomed to adjusting the idle mixture with the engine running, I did manage to try adjustments with long thin screwdrivers with some success however, the engine was simply not responding. I have now checked the carbs and see no problems, I am curious to the heating up of the enging, I have seen comments that the ski should be level and the hose not turned full on, at the moment the one I have been working on is facing downhill, I am thinking this is what was casuing the hot running? So, today will see me refit the carbs and make my own inlet gaskets with gasket paper, I will pull the fuel valve from the fuel tank and check the filter in there, then fit the carbs, then get the motor level and then spin her over to see what happens.


    I hear you about the primers, if my friend intends to keep this motor I will see if he wants to get some fitted, with the rumour that 2 strokes are on the way out and that the parts supply for these is drying up he may get rid of it.
    I will get back to you and the forum, you never know it may help someone else?

    Thanks again

    regards

    Dave

  7. #7
    Pain is fear leaving your body.... rlovebk's Avatar
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    For a resource for parts on these check John Zigler at Rock County Jet Ski. He deals in used parts. I would get rid of the CV carbs. They are not the best and most could never tune low speed circuit on these carbs and most believe it is due to their design. I am sure Zigler will deal international as he is a business man and likes to do business. I know 44's work well on these ski's but I do not recall method of adaption/manifold. Kiehin or Mikuni's will get you where you want to go.

    Primers ok on CV carbs but interfere with butterfly operation many times. I am not familiar enough to advise as to placement.

    As far as on the hose ski is best leveled or tilted back, not front (bow) down for sure. A good flow, just not full blast, is needed. You should not run too long on hose as most 2 strokes were not plumbed for full cooling on hose although yours may be.

    Wish I had more technical knowledge to share but I don't.
    Good luck.

  8. #8
    OK some feedback, first many thanks to all that contributed, we are very grateful.

    Having checked the carbs with the small filters, new hull filter I decided to pull the fuel pickup out of the tank, it was minging as was the muddy fuel at the bottom. It seemed that once the sediment had settled you could start it and run ok for a short while, the return fuel turbulence must have stirred up the rubbish and blocked the pickup filter, changing to RES would cure it for a short while until this too also got blocked. Cleaned this out and now it goes really well, when on the hose we also noted some water running from the back of the craft and thought this was down to the bow down attitude of the ski on the trailer.

    Now we have a great ski but water coming in from the rear, something it has never done, no hoses appear to be off, should I start another thread? On the water the ski is running perfect bar the water coming in from the rear.

    Many thanks again for the help....what now?

    regards

    Dave

  9. #9
    Pain is fear leaving your body.... rlovebk's Avatar
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    Leave the ski tied down to the trailer, (fore and aft) and back it into the water. Pull the seats and check it out. If you do not find it then start the ski up and look and see what you find.

  10. #10
    Pain is fear leaving your body.... rlovebk's Avatar
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    Leave the ski tied down to the trailer, (fore and aft) and back it into the water. Pull the seats and check it out. If you do not find it then start the ski up, (still tied down) and look and see what you find.

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