• If this is your first visit to the iboats.com Boating Forums, be sure to check out the FAQ. To post a question or comment, begin by signing up. To start viewing messages, select the forum that you want to visit from the selection below.
  • ALL iboats Forum Members and Guests:
    To show our appreciation for your participation in the Forums, we're offering an exclusive Forums-only discount good for an additional 5% off your iboats.com order for a limited time.
    To redeem, simply call our Customer Service Team at 800-914-1123 (Open M-F, 9am - 8pm Eastern Time) and mention the Forums 5% off discount. Offer excludes engines, trolling motors, and electronics.

Announcement

Announcement Module
Collapse

Help Tip: If you have a question that has not been answered to your satisfaction in the archives, it is always best to start a new thread of your own. By starting your own thread, you will receive the maximum number of views by forum members.

Below are some additional forum policies in hopes of all iboats members will follow, Thank you.

1. Please do not reply to old threads or hijack existing threads. Old threads of a technical nature are like a library book, Please do not write in them.

2. Old threads should be considered archives and used for reference only. Please do not reply to them.

3. Do not take over someone elseís thread (aka hijack) with your own question, even if it is similar. If you have a question that has not been covered to your satisfaction in the archives, it is always best to start a new thread of your own.

4. If you have a question for the original poster (OP) and the thread is over 30 days old, send the OP a PM, he may not even visit the forums any longer, or may not notice your question in the old thread.

5. By starting your own thread, you will receive the maximum number of views by forum helpers that may not even notice your question when itís posted at the end of someone elseís thread. And those answers will be specific to your particular issue.

6. Please do not post to threads that have been inactive for more than 3 months unless you are the original poster. We have very active forums and any thread that remains inactive for that long should be considered "dead". It is especially confusing when there is an entirely new question posted to an old thread.

7. Posting at the end of any thread is considered to be hijacking the original posters thread which in turn subjects the thread to be closed if it continues to happen thus not making it fair to the original poster in the future had for some reason he/she needed to return for additional information or provide an update of the problem solved which is always welcomed within a reasonable amount of time frame.

8. Please note that you should see a red banner pop up near the bottom of each inactive thread asking you not to reply to old threads. The Red banner will read: Please note this thread has been inactive for 90 days. For the best results, please start a new thread.

Thank you all in advance for doing your part in helping iboats run a smooth ship.

Additional forum rules linked below.
http://forums.iboats.com/forum-rules-guidelines-405/
See more
See less

can't go over 4600rpm @ WOT 115 yamaha 2-stroke

Page Title Module
Move Remove Collapse
X
Conversation Detail Module
Collapse
  • Filter
  • Time
  • Show
Clear All
new posts


  • can't go over 4600rpm @ WOT 115 yamaha 2-stroke

    Bought a used boat recently
    1982 16" fiberglass sportcraft open bow with 1990 Yamaha V4 115 2-stroke.
    The boat is a light (1400lbs loaded with 2 people in it) 16" v-hull/hybrid boat. It is rated for a max of 110hp.
    The propeller is a yamaha 13" X 21 pitch stainless. Max speed is 39mph alone (GPS tested). 37mph with 3 people. This boat defies logic and I'm trying to find the reason why it's so slow.

    I researched other similar boats and most of them are well over 40mph. Most of the them in the 45mph-47mph range and are able to hit 5300rpm+ with this size of propeller.

    What I've checked:
    -120psi compression on all cylinders.
    -new spark plugs well gapped
    -tried mounting the engine 1" higher to make the anti-cavitation plate line up with the bottom of the boat. This result in the same speed +-.5 mph with a lot slower acceleration due to prop venting. Also the boat can't turn hard now for the same reason. With the engine in the original position when the trim is down the boat handles very well.

    How the engine runs:
    never stalls seems to run really well, no hiccups or up and down rpm at WOT. Excellent acceleration out of the hole, shoot out and gets on plane very quickly. Hit 30 mph in around 5-6 seconds.
    But it just seems to not want to go over 4600rpm. Unless I overtrim the engine and lose a bit of mph. Trimming from bottom adds about 2.5mph.

    Next thing I need to check is Ignition timing and I ordered a 19 pitch aluminum propeller by turning point prop.

    Another note for the performance aspect is the boat has been repaired a few times and the bottom is kinda rough. A few patches not well sanded down and such. I don't know how bad this can affect top speed.

    Any other ideas or comments ?
    Attached Files


  • #2
    Re: can't go over 4600rpm @ WOT 115 yamaha 2-stroke

    you shouldrun well over that.
    5500 or so.you may be over proped
    good luck benny 1963








    ,
    Benny B

    Comment



    • #3
      Re: can't go over 4600rpm @ WOT 115 yamaha 2-stroke

      Originally posted by Benny1963 View Post
      you shouldrun well over that.
      5500 or so.you may be over proped
      good luck benny 1963

      ,
      Maybe, but what I don't understand is this:

      Normally when a boat is over proped, adding weight slows the boat down a lot, especially in a light boat. I barely slow down adding 400lbs.
      Also the boat did not go faster by raising the engine 1". This doesn't make any sense. The engine shoots so fast to max RPM but then but hits a wall at around 4500rpm. You need to use a lot of trim to go up to 4600-4700rpm and even then most of it is slipping.

      Also a 21 pitch 13" prop isn't that big of a prop for a light 16' fiberglass boat ?
      Maybe I'm expecting too much out of the 115 yammie.

      Comment



      • #4
        Re: can't go over 4600rpm @ WOT 115 yamaha 2-stroke

        I have a 16 foot 1977 Skeeter that I just added an 1993 Yammie 115. It instantly gets up to 50mph and has a Alum. 17pitch on it. RPM are more then you say, maybe your boat hull is slowing it down somehow?

        Comment



        • #5
          Re: can't go over 4600rpm @ WOT 115 yamaha 2-stroke

          Originally posted by 72Glastron View Post
          I have a 16 foot 1977 Skeeter that I just added an 1993 Yammie 115. It instantly gets up to 50mph and has a Alum. 17pitch on it. RPM are more then you say, maybe your boat hull is slowing it down somehow?
          What rpm are you turning with that prop @ 50 mph ?

          My fish finder says I do 47-50mph. But GPS says 37-39mph depending on conditions.

          My rpms do sound like they are @ 4500rpm. I have the yamaha digital gauge and it is set for the correct engine.

          I am starting to think that because the stern of the boat is shaped like a tri-hull in the back. When on a plane the boat has tri-hull type resistance causing low max speed. I should post a pic of the hull to figure out if it's one of the low efficiency one.

          Comment



          • #6
            Re: can't go over 4600rpm @ WOT 115 yamaha 2-stroke

            any other input ?
            I want to try something today.

            For checking ignition timing @ Wot with the boat out of the water I read somewhere about a trick ?
            I don't recall the exact procedure. Anyone knows how to do it ?
            I have a timing gun

            1990 Yamaha 115 2-stroke

            Comment



            • #7
              Re: can't go over 4600rpm @ WOT 115 yamaha 2-stroke

              go to a good dealership,rent their test wheel. if the motor will spin it your over propped,if it wont you have engine issues.
              no tech questions by PM, they wont get answered.
              you have to be trusted by the people that you lie to .

              Comment



              • #8
                Re: can't go over 4600rpm @ WOT 115 yamaha 2-stroke

                Originally posted by rodbolt View Post
                go to a good dealership,rent their test wheel. if the motor will spin it your over propped,if it wont you have engine issues.
                Good idea !! sweet. That takes away the boat as a factor.

                Comment



                • #9
                  Re: can't go over 4600rpm @ WOT 115 yamaha 2-stroke

                  yes it does.
                  and on a boat with an unknown history its the only way to seperate hull/prop issues from engine issues.
                  you would not belive the amount of new rigs we get that are way overpropped from the factory.
                  used gets even worse sometimes with Ebay and such.
                  no tech questions by PM, they wont get answered.
                  you have to be trusted by the people that you lie to .

                  Comment



                  • #10
                    Re: can't go over 4600rpm @ WOT 115 yamaha 2-stroke

                    We will know soon with a new aluminum 19 pitch prop from turning point propellers.

                    Checked timing advance today. Perfect at idle part throttle and WOT. 25btdc @ wot and 5 btdc @ idle.

                    I checked something else today. I use portable tanks. And the primer bulb is pretty firm normally. However at WOT the bulb goes soft and there seems to be a vacuum created. I tried pumping it but it stays soft and sucked up.
                    Don't know if this is normal. Going to 2/3 throttle the bulb pumps back up.
                    Maybe I have a vent issue on the tanks ? Could this cause a lower than normal fuel pressure and lean out @ wot.

                    Comment



                    • #11
                      Re: can't go over 4600rpm @ WOT 115 yamaha 2-stroke

                      I just tested the turning point prop on my yamaha 115

                      What's nice is that I went from a stainless steel 21 pitch that did 39mph @ 4600rpm
                      to an Aluminum 19 pitch that does 40mph @ 4900 rpm. The prop cost me 70$
                      I do a lot of fishing on an old logging river. There aren't many logs around anymore but once in a while you see one floating by.

                      When I raised the engine the 21 pitch yamaha ventilated quite a bit.
                      I did not change engine height and now barely have any ventilation. Much better acceleration and handling. Also I can trim the engine so much more now and gain speed. Still 40mph is all I got trimmed out @ 4900rpm.

                      What's strange is the 19 pitch prop runs 36.5mph @ 4600rpm with the engine trimmed down. Similar to the yamaha 21 pitch. It just allows me to trim the engine quite a bit more without ventilating.

                      Comment

                      Working...
                      X