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90 hp yamaha 2 stroke need help with wot!!??

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  • 90 hp yamaha 2 stroke need help with wot!!??

    I have just purchased a 19' polar fiberglass boat with a c90tlrv yamaha 2 stroke on it. I have ran a compression test and come up with 100-105 psi on all three cylns. I also ran a spark test and with a 7/16 gap and got a strong blue spark. I sync. the carbs and the linkages and also used a dial indicator to get TDC of #1 to set the timming mark and set the ign timming to 8 degrees atdc. The boat has a new fual tank and fuel line with inline filter. fresh non-ethinol 50:1 mix. It will start up great and idle well no caughing or sneezing. When i put it in the water I can not get it to come up to WOT in fact the boat will not even get up on plane. any ideas please!!!. and P.S. I have a rapture SS prop 13-1/4 X 19 on it and the keel is aprox 1 to 1-1/2 inches above the bottom of the boat.

  • #2
    Re: 90 hp yamaha 2 stroke need help with wot!!??

    That is a large pitch prop for that size motor and boat. What is your max rpm? And your antiventilation plate should rigged be about 1 to 1.3-1.5 inches above the keel depending on water pressure.
    DO YOU HAVE: GOOD COMPRESSION, PROPERLY TIMED SPARK, PROPER FUEL AIR MIXTURE?

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    • #3
      Re: 90 hp yamaha 2 stroke need help with wot!!??

      Check fuel pump maybe order new one and get new gasket for back. If screws are loose it wont allow top rpm. You should be running 17pitch alum. If running stainless I would suggest 16pitch but 17 is better than your current setup. I picked up 500 rpm with fuel pump kit installed. Getting 4500 rpm at 5200 alititude with 17k. May try my 15pitch soon.

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      • #4
        Re: 90 hp yamaha 2 stroke need help with wot!!??

        http://www.yamaha-motor.com/outboard.../perfbull.aspx

        Look here and see what a boat like yours should be doing and what size prop was used. If yours can not get close to that then you have a motor problem.

        My guess would be fuel related, but a test run with the Yamaha test prop will tell you if the motor is producing the proper HP

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        • #5
          Re: 90 hp yamaha 2 stroke need help with wot!!??

          If you were losing spark on one cylinder it might start up and idle fine and then not run up to WOT plane speed. Maybe a bad/fouled plug/wire/coil? Maybe bad fuel pump diaphragm causing very rich fuel mixture on that plug?

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          • #6
            Re: 90 hp yamaha 2 stroke need help with wot!!??

            Ok so I need to hook up my tachometer. The boat was previously owned and I need help hooking up the tachometer to the yamaha 90 wiring harness I didn't know what wires to use. I have the tachometer that was in the console. It is a Yamaha digital marine meter with the trim indicator and three warning lights. At this point I only need to know which wires to use any suggestions??

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            • #7
              Re: 90 hp yamaha 2 stroke need help with wot!!??

              You have the same exact motor as mine. Put in new/clean plugs,take the boat for a run on the lake, turn off motor and pull plugs to see which one may not be firing or which cylinder has the problem. The weak/bad cylinder plug may have more carbon on it. May be that fuel pump diaphragm or plugged carb jet. Good Luck!

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              • #8
                Re: 90 hp yamaha 2 stroke need help with wot!!??

                Are you certain the throttles are opening fully. Even if the throttle lever is fully forward, you need to look into the carburetor bores to ensure the throttle plates are perfectly horizontal in the bore.

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                • #9
                  Re: 90 hp yamaha 2 stroke need help with wot!!??

                  i have checked the carbs they are opening all the way. I will be changing the fuel pump this weekend and giving it another try but i really need to hook up this tachometer so I can tune the engine properly. Does any know which wires to use for this ?? do all tachs use the same color wires?? which wires do I need to use on my harness I dont have any plugs so I am going to have to solder and splice the wires together. any help would be greatly appreciated!!

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                  • #10
                    Re: 90 hp yamaha 2 stroke need help with wot!!??

                    Yamaha tach signal is green. American (Merc and OMC) are gray. So if your boat is wired for an American motor you would use the gray wire on the boat side, but green wire is where the signal comes from the motor. I know it's stupid...
                    DO YOU HAVE: GOOD COMPRESSION, PROPERLY TIMED SPARK, PROPER FUEL AIR MIXTURE?

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                    • #11
                      Re: 90 hp yamaha 2 stroke need help with wot!!??

                      Ok I came home this weekend and I have installed a new fuel pump, cleaned all three carbs by fully taking them apart and soaking them for aprox 45mins to 1 hr in carb cleaner then cleaned them with compressed air and reassembled them. have to say they were darn clean. I also inspected the idle adjustment screw and float valve they did not have any apperance of ridges on them. I put them back on the motor and also installed all new fuel lines,vacume linesw and new clamps at all terminations. I installed a tach to the motor and set all the linkages to spec I also set the idle timing to 8 degrees ATDC this thing sounded and ran great in a tank. set the WOT stopper to match the mark on the CDI. I then took it down to the river and put the motor in the water so I could run it at WOT under a load but I am only able to get 2400 RPM. The carbs are fully open butterflies are horizontal on all three. The only way i can get it to 5000 RPM is to trim it way up and it shoots water 20' in the air. Their is something wrong I have ran three seperate compression tests with two different gauges and all three times I came up with 105 PSI on all three cylns. also ran a spark test with 7/16 gap wery strong blue spark . tested the motor at the river with a boatside fuel tank. PLEASE ANY BODY I NEED HELP I am pretty knowledgable on mechanics although this is my first marine engine but my goodness this thing is winning so far so ANYBODY HELP HELP HELP!!!

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                      • #12
                        Re: 90 hp yamaha 2 stroke need help with wot!!??

                        P.S. I also checked my prop it is a 13-1/4 x 15" SS three blade

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                        • #13
                          Re: 90 hp yamaha 2 stroke need help with wot!!??

                          Ok maybe this is a stupid question but, can i test the WOT of my motor while the boat is on the trailer with the motor in the water or does the motor need the momentum of the boat to acheive its WOT?? ( 5000 + RPM )

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                          • #14
                            Re: 90 hp yamaha 2 stroke need help with wot!!??

                            Have you checked the overheat temperature alarm circuit with the pink wire from thermal switch on back top starboard side of cylinder head? Maybe motor is stuck in the safety/reduced RPM mode by that circuit? Just an idea, since it sounds like you've checked everything else. Good Luck!

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                            • #15
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                              Re: 90 hp yamaha 2 stroke need help with wot!!??

                              Originally posted by THE OPERATOR View Post
                              Ok maybe this is a stupid question but, can i test the WOT of my motor while the boat is on the trailer with the motor in the water or does the motor need the momentum of the boat to acheive its WOT?? ( 5000 + RPM )
                              It would be best to have the motor run with the Yamaha test prop to see if the motor is putting out the proper RPM and HP. That can be done on the trailer in the water. If it will not then you have a motor problem, and if it will then you have a boat or set up problem.

                              As long as the linkage is against the WOT stop then you can check WOT timing with a timing light.
                              I have done it by taking the linkage loose and just moving the wiper to the WOT mark while idling, but by doing it while running on the water it will tell you that the motor is getting the proper advance while loaded up.

                              I do not believe the motor will get to the proper WOT RPM with out the boat moving across the water as it will be loaded too heavily. That is why it helps to use the test prop, as it is made to be tested without running across the water.
                              You have stated 2 different pitch props on this boat which is the correct one.

                              If I had to guess I would say carbs problems still, but hard to test that.

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