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94' Yamaha 115 2 stroke won't idle

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  • 94' Yamaha 115 2 stroke won't idle

    motor will start with choke on, off once started. have to keep fast idle around 1500 rpms to keep motor running. if i drop fast idle and put into gear quickly it will stay running but if i give it any more throttle than 1500 rpm it floods out and dies. if i go through this starting process and leave it run at 1500 rpm for about a minute it will eventually clear and start to run smoother then i can hammer down and it runs great, if i put throttle back to neutrel it dies.

    ive replaced spark plugs and opened and cleaned carburators. the needle valves are rubber and they do have a line around the point where they seat. ive been told they are the problem and to rebuild the carbs. ive also been told by one guy that i have spark issues.

    if it runs strong after it clears at 1500 rpm for a minute that would eliminate the electrical issue right? im hoping its the carbs, im waiting for the rebuild kits to arrive any day now.

    any input would be greatly appreciated.
    thanks.

  • #2
    Carbs

    But I am guessing fuel related so it could be number of things. Your quick connect for fuel is oring in place does any gas dribble down? I just put oring from ACE harware for faucets and bulb gets hard now! Thicker oring slightly bigger. Fuel pump diaphram kit is needed for your model if not done yet. You can start taking the carbs off and looking at them. Number each one and it's position, for high speed jet count the turns down and try to get them in same as installed. Rebuild parts may not be needed just good cleaning and oiling rubber gaskets. Obviously you need to set pilot screws correct if it runs and sputters all out I turned mine clockwise 1/8 to 1/4 leaner. 520 degrees out it or 1 1/2 turns
    Last edited by 200090tlry; 08-24-2011, 01:01 AM.

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    • #3
      i dont think there is a quick connect for the fuel line, it has a inboard tank that is plumbed directly into the motor. ive by passed this and ran out of a jerry can to eliminate any tank or bad fuel possiblities. are you saying the fuel pump diaphram needs to be rebuilt? why do you suggest this? how can i tell if its not pumping fuel properly? or do you just reccomend it gets replaced? ive already taken the carbs apart and cleaned, i didnt oil any gaskets though.

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      • #4
        Just from what you have desribed

        Sounds like motor is running rich, what are your pilot screws set at. Do you have the manual on motor. Mines 1 1/2 but does the same thing your describe I turned clockwise 1/8 to 1/4 and it runs way better all out. Could also be a sign of weaker spark but I would first try fuel solutions. Fuel pumps are a good idea to replace on an older used motor. I found on Mercury's they have issues and took my awhile to solve my issues with overoiling lack of fuel. Well the little rubber was fliped around on one side and turns out was problem. Im not that familiar with Yamahas fuel pumps they do seem like a superior product but I replaced mine so I am not chasing any gremlins. Ordered all parts for my new used motor at one time. What altitude are you running
        Last edited by 200090tlry; 08-24-2011, 04:45 AM.

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        • #5
          pilot screws are at 3/4, i was told between 5/8 and 7/8 are yamaha recomendations. i just removed the idle jets and cleaned them and the ports as best i could without removing carb again (they are in the front so they were easy to get at). i also removed spark plugs (they were wet and a little black) cleaned them and tried running again. no luck still runs rough at low to mid rpm and wont idle. if i remove a spark plug and turn the motor over i get a small but consistant spark on all cylinders. i asume this spark gets brighter with rpm because it runs off of a magneto? or should they all be strong at idle? could all 4 coil packs be bad at the same time? i dont think they would but i may be wrong. is there a way to check coil pack with an ohm meter?

          thank you for your help so far!!

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          • #6
            pilot screws are at 3/4, i was told between 5/8 and 7/8 are yamaha recomendations. i just removed the idle jets and cleaned them and the ports as best i could without removing carb again (they are in the front so they were easy to get at). i also removed spark plugs (they were wet and a little black) cleaned them and tried running again. no luck still runs rough at low to mid rpm and wont idle. if i remove a spark plug and turn the motor over i get a small but consistant spark on all cylinders. i asume this spark gets brighter with rpm because it runs off of a magneto? or should they all be strong at idle? could all 4 coil packs be bad at the same time? i dont think they would but i may be wrong. is there a way to check coil pack with an ohm meter?

            altitude is 1893ft.

            thank you for your help so far!!

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            • #7
              Just looked in my book

              3/8s to 7/8s for 97-98 the newer outboards are more screws out. Im guessing yours will be same 97s. Have you put new plugs in motor exact same NGKs brhs-10 Oriely's has them. Once you have looked everything over and still not working good then you can move on to reeds,compression check.

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              • #8
                Update

                just finished rebuilding the carbs, adjusted one float so all 4 are now .630". as i was putting the carbs back together however i realized one of the air mixture screws is badly worn, the other three look a little worn but not too bad in my opinion. i installed the carbs and tried running the motor anyway and it runs strong except it still wont idle. it dies out under 1500 rpm. can these air mixture screws be the culprit? dont know what to do next (after replacing thes mixture screws of course)

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                • #9
                  My bets are on fuel-related issue.

                  Thoroughly clean carbs
                  Replace worn needle valves.
                  Replace air mixture screws.
                  Note that air mixture screws do NOT adjust richness, just quantity.
                  Yamaha recommends 3/8-7/8 turns for your motor.
                  Lastly check your fuel pump (pressurize it to exclude any leaks in the engine)

                  Good luck

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                  • #10
                    is there a way i can check if the fuel pump is working properly?

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                    • #11
                      Yes, it is analytically explained in Yamaha manual of your motor.
                      You just need a vacuum pump with a gauge, and some disassembly before you start

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                      • #12
                        Scott W C.

                        While not the same motor, I had idle issues with our 90 TLRD. After the third time through the carburetors, I believe my problem was clogged pilot jets. As I understand, the pilot jets provide fuel at idle while the main jet provides fuel under power with throttle open.

                        On only one of my three carburetors could I remove the pilot jet. The others were too stuck to risk. I ran a bristle from a brass wire brush along the passage from both the bowl side and throttle body side. I also blasted the passage with store brand carburetor cleaner and compressed air from both sides until I felt a good blast of air from one side to the other.

                        My issue was from ethanol eating the aged fuel hoses. The carburetors were choked with crap. Even the bowl drain was plugged. If your lines, bulb, etc. are more than 4 years old, I suggest a complete replacement including fuel pick-up tube and if you don't have one, a 10 micron water separating fuel filter. I also use Stabil Marine fuel stabilizer religiously.

                        I suggest Yamaha's service manual that is easily purchased online. After the first use, the expense is incidental. Also, gaskets are easily available here.

                        Since it runs at 1500 rpms, I wouldn't suspect the fuel pump. I'm also not sure if testing will take less time or money than just dissemble, inspect and replace suspect parts.

                        This is pure conjecture. Our middle carburetor has the electrothermal valve (fancy choke) and emergency starter assembly. Ours was miss assembled by the prior owner's reputable marina. If yours has similar and is experiencing difficulty, they could be dumping fuel making the mixture too rich to run at idle.

                        Hope this helps, good luck and keep us posted.

                        BTW, Last Saturday I was returning on the emergency ferry from Rodanthe, Hatteras Island, NC chit chatting with good friend Cpt. Rudy about another's Merc Verado. He noted that near everyone on the Outer Banks runs Yamaha's because they don't like working on weekends.

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                        • #13
                          I recently replaced the damaged air mixture screws I had spoke about and the engine is now idling nicely at around 700 rpm. So from start to finish I rebuilt the carbs (also had to adjust one of the floats was baddly out of tollerance) and replaced spark plugs. (air mixture screws do not come with rebuild kit, I recommend ordering them along with rebuild kit) Looks like I've fixed the problem, it was a combination of a float being out of tune and causing the flooding and the bad air screws that lead to my problems. I havn't had it on the water yet, just running with the muffs on. (I hope I'm not jinxing myself hahaha) Thank you for all your help I appreciated every response I recieved!
                          Last edited by Scott W C.; 09-27-2011, 12:35 AM.

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