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95 TS Daytons 640 uncontrolled revving

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  • 95 TS Daytons 640 uncontrolled revving

    I have searched through the documents on here and learned much, but nothing seems to address my problem.

    I have just started working on this TS about a week ago. The block was rebuilt last year, but I am not sure if the carbs were also rebuilt. They don't look it, but I don't know for sure.

    My problem is when I crank it up out of water, it will idle for 5-10 minutes fine, then just rev so high that it shuts itself off for no reason. If I start it up again, and give it full throttle, it will rev up then die. The rpm's go beyond the 8000 on the tach, so I am not sure if this is normal. Should there be some kind of rev limiter on this pwc?

    Anyways, I thought maybe its the carbs, but why would they just start revving for no reason? I didn't see any of the butterflys sticking.

    Any suggestions would be greatly appreciated.

    Patrick

  • #2
    You are leaning it out so much it's glowplugging. The sparkplugs are getting so hot they light the fuel mixture just from the heat - the rev limiter is electronic, it does nothing for a mechanical runaway. You are doing severe damage by doing this.

    Yes the carbs are the first parts to check, also you need to do a case pressurization check to make sure you don't have a breach. Somewhere you have an airleak, or your carbs low circuits are extremely clogged or set lean.
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    • #3
      I have taken your advice and richen the low mixture and now it seems that it is idling at around 2500 rpms.

      Now the problem is that it will idle for about 5-10 minutes and then just die. No rev, nothing.

      BTW-During these mechanical runaways, I have been trying to cut if off, since I can only imagine the amount of damage that can happen at those rpms. I have been mostly successful with this, but i missed it a couple of times :(

      Patrick

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      • #4
        I am confused as to what you mean by case pressurization. Is that the 150psi cylinder pressure I keep reading about elsewhere?

        I am also new to two-strokes, so if you could explain carb "low circuits," I would be greatly appreciative.

        Sorry for all the Noob questions. I am good with cars, but these dual carb, 2-strokes are killing me.

        Patrick

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        • #5
          To cure a runaway pull the lanyard off, pull the choke open and hold the throttle wide open. If you have a primer pump it until it dies.

          The low circuit is adjusted through the low speed mixture screws you adjusted.

          It sounds like you are in the right neighborhood now, where exactly do you have the screws adjusted to now? Does the ski have any mods?

          no case pressurization is making sure the case is air tight and doesn't have any seam or seal leaks. It's done to 7-10 psi. You are thinking of cranking compression.
          SBT Tech Support is here to help with your problems.
          We try to answer each question quickly and accurately.
          Please do not use Private Messaging for Tech Support, use the forums.

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          • #6
            Wow, sorry, I have no idea how many turns from closed they are. It was a minor change on the low end (maybe 1/4-1/2 turn from original position. From my reading, I have gathered that clockwise is lean, counter clockwise is rich.

            Busted the choke cable trying to stop it one time it ran away (hasn't ran away since the adjustments). Guess I am going to have to buy a new one of those now (you guys sell em?).

            No mods that I am aware of. Just a couple of Mikuni carbs (I think they are 38mm. They are stock). She is still cutting out after a while at idle. I checked the fuel filter for possible stoppage, but it blew thru clean.

            Now, I guess I have to work on the high end. The ski will rev, but die out in the top end like its flooding. I am going to try to lean out the high end using the same methods as richening the low end.

            If i could just get her to idle indefinitely, I will feel like I have gotten somewhere with her.

            Thanks for the help. I am sure I will be doing business with you shortly [img]/graemlins/winkanim.gif[/img]

            Patrick

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            • #7
              You should remove the carbs and give them a clean before you chase your tail around.There's a fuel filter in the carburetor as well as the external one you cleaned.Cutting out at full throttle maybe starving,not flooding.Sometimes they cut out after a while idling cause the plugs oil up from an over rich mixture...non of mine will idle for ten minutes..and hey what you want to idle for?!!Do you run premix? Your idle speed is set by the cable adjust, not the jet..be carefull.

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              • #8
                I wanted to make sure you were running it in the water or a flush kit. If you run it for 5-10 min without cooling it will overheat and die.

                Remember to use proper flushing procedure.
                engine on, water on, water off, engine off.

                Be carefull on the high speed setting not to make it too lean and burn or sieze a piston.
                The stock settings should be good if is has not been modified. I can look them up and post tomorow.

                If your settings now are a lot richer then the stock setting especialy the low speed,I would suspect water or debris in the carbs, rebuild them. They sell the kits here. Afeter setting to stock follow the carb adjustment procedure in the tech section here.

                I should have a used choke cable and will let you know.
                Providing mobile JetSki service to the Charlotte / Lake Wylie area.

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                • #9
                  Russ you posted that the same time I did so I second what you said.
                  Providing mobile JetSki service to the Charlotte / Lake Wylie area.

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                  • #10
                    Originally posted by russthemuss:
                    You should remove the carbs and give them a clean before you chase your tail around.There's a fuel filter in the carburetor as well as the external one you cleaned.Cutting out at full throttle maybe starving,not flooding.Sometimes they cut out after a while idling cause the plugs oil up from an over rich mixture...non of mine will idle for ten minutes..and hey what you want to idle for?!!Do you run premix? Your idle speed is set by the cable adjust, not the jet..be carefull.
                    Ok, tomorrow i plan on removing the carbs and throughly cleaning them with a bottle of carb cleaner. I have gotten more information on this ski today. The carbs have never had any work done to them, so I assume a rebuild is in order (Its been 8 years or so).

                    As I understand it, the oil/gas mix is made on the fly (two seperate tanks), so, no, it's not premix.

                    i have been setting my idle via the idle screw on the carbs, not by the mixture screws. The only issue I am having is that it will idle for a few minutes at say 2500, then run up to maybe 3200 for about 30 seconds, then fall back so quickly that i have to choke it to keep it going.

                    Hope that gives you a little more insight into these issues I am having. I am thoroughly enjoying working on this (my first 2-cycle motor), and everyone's help has made the busted knuckles worth the effort. There is already progress.

                    Thanks for all the advice

                    Patrick

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                    • #11
                      Originally posted by dank:
                      I wanted to make sure you were running it in the water or a flush kit. If you run it for 5-10 min without cooling it will overheat and die.

                      Remember to use proper flushing procedure.
                      engine on, water on, water off, engine off.

                      Be carefull on the high speed setting not to make it too lean and burn or sieze a piston.
                      The stock settings should be good if is has not been modified. I can look them up and post tomorow.

                      If your settings now are a lot richer then the stock setting especialy the low speed,I would suspect water or debris in the carbs, rebuild them. They sell the kits here. Afeter setting to stock follow the carb adjustment procedure in the tech section here.

                      I should have a used choke cable and will let you know.
                      I am currently running it on a hose in my backyard. I have pretty good pressure and the block never gets any hotter than "warm to the touch." i assume its not overheating, but there may be more to the heat dissipation than meets my eye.

                      I have recently learned the proper method of flushing only recently (found the forum today). I have since used this method. I have not noticed the plugs getting a whitish substance on them, so I don't think I suffer from some of the symptoms of bad flushing technique.

                      I have not really started into the high mixture settings, due to the fact that I suspect dirty carbs. I figure any adjustment I make now will be null after the carbs are placed back on the intake manifold. I will keep the leanness issue in mind when I go to make that adjustment.

                      Please post any factory default settings you have. I am sure that would make a world of difference, and at least give me a starting point. The plugs are so black now, I can't even gauge my richness. I am going to have to replace these plugs soon.

                      In addition, the block has recently been rebuilt (less than 12 hours on it), and I was idling it to help break it in. The problem is the engine block (new crank, bearings, rings, pistons, ect) was rebuilt last fall, and the engine was never broke in before it was put away for the winter. I don't know if this has effected anything, but it starts up fine (with priming) and runs relatively good, considering I know nothing of the innards of a 2-cycle carb. I could be completely a$$ backwards, and that wouldn't surprise me, but I am not completely ignorant of how a gasoline powered motor works.

                      If you have a choke cable, I would gladly pay you for it. I currently have a paypal account and can pay immediately to your account if you have one also.

                      Thanks again guys. Your help is invaluable, and if I could, you all would be invited over for beer and golf.

                      Patrick

                      [ April 01, 2003, 02:45 AM: Message edited by: tn_pmm8647 ]

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                      • #12
                        Sounds like you are on the right track now. It seams to be running lean causing the idle to climb. This can be the filters or fuel pump. or lines.

                        Make sure you drain out the old fuel if it has been in there all winter.

                        Get a rebuild kit before you take the carbs apart. If you need something there is less chance of looseing something or forgeting how it goes back together if you do it right then.

                        Once you get the carbs clean and set to factory settings you will have to check the jetting with the ski in the water under load. On the trailer will not tell you much.
                        Providing mobile JetSki service to the Charlotte / Lake Wylie area.

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                        • #13
                          Stock settings:

                          High screw: not specified
                          Low screw: 7/8 turn out
                          SBT Tech Support is here to help with your problems.
                          We try to answer each question quickly and accurately.
                          Please do not use Private Messaging for Tech Support, use the forums.

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                          • #14
                            Well, I can assure you that the carbs are far more than 7/8 of a turn out on the low side. Probably sitting at least 1 or 2 complete turns out. The ski won't run if it is turned in that far, but that is without a carb rebuild.

                            Patrick

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                            • #15
                              Then you know what your next step is.
                              SBT Tech Support is here to help with your problems.
                              We try to answer each question quickly and accurately.
                              Please do not use Private Messaging for Tech Support, use the forums.

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