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New 9.8 4stroke: Rev limiter during break in period?

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  • New 9.8 4stroke: Rev limiter during break in period?

    After much self-debate about the new 9.9/15/20 family vs carbed 4s 9.8, I just bought a new 9.8 for my light 12ft aluminum vee. I have about 5 gentle break-in hours on it and just got a little inductive hour/tachometer, which showed me some surprises.

    It runs 16mph at less than half throttle (100lb boat plus 170lb me). Manual says I can now do short blasts of “full” throttle. When I do, revs go from 2800 at half throttle up to 3000 at full then fall slightly to about 2800ish. Speed doesn’t pick up much, maybe 3 mph.

    Specs say say it should hit 5-6k rpm and I know I’m not overpropped in my tiny boat. Does this thing have a rev limiter keeping it under 3k while breaking in? I think I have the tach set up right, it’s saying 1k at neutral idle and 800 in fwd idle.

  • #2
    Owner's Manuals tell you stuff like that.
    BOAT SPECS FORUM HELP STARCRAFT FORUM SHOP iboats
    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
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    • #3
      Nope.

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      • #4
        Originally posted by Mcboatface View Post
        Nope.
        Then it isn't rev limiting during break-in. The book would say that to stop unnecessary warranty claims for poor performance.
        BOAT SPECS FORUM HELP STARCRAFT FORUM SHOP iboats
        Please, no PM's (Private Messages) regarding boat/engine problems.
        That is what the forums are for.
        Only forum/moderator issues will be answered in PM's.

        Comment


        • #5
          Tach is probably wrong. Idle spec is 950 in N, and 900 in gear. Many people set that a hair higher for better warm-up, unless they have an RC setup with neutral warm-up lever.
          Max WOT RPM is 6000. Recommended top RPM of 5000 to 6000. Higher is better. There is an ignition-staggering rev limiter, which engages at about 6250.
          This is a siamese ignition coil; Both plugs fire once each revolution -- that means once at the power stroke, and again on exhaust... If you set the tach correctly, you should be OK.
          Paul
          Buffalo NY USA

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          • #6
            That’s got to be the issue - thanks Paul. Will try the other tach modes and report back. Also, if I’m hitting high cruising speed at less than half throttle, then quickly bouncing off the governor, then I take it I can go up a prop pitch or two

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            • #7
              Interesting. So, let’s say 5000 rpm. Gear reduction is 2.08. Stock pitch is (I think, couldn’t find the mark in the dark on the water) 8.3. Assume 10% slip. Comes up to 18mph on my napkin calculator. So, no way was I getting fuel cut at 3k rpm at 18mph. Tach has to be wrong.

              Reset tach setting to 1 pulse : 1 rotation and got (seemingly) accurate rpm readings over 4300rpm. Below that, rpm readings were doubled. Weird. On the previous setting I had before, described in first post, rpms seemed right at lower rpm but obviously were wrong at high rpm. Not sure if I have a bad tach or if there’s a quirk of this ignition system I don’t understand yet. Anyone else w similar issue or recommend alternative tach? Im using the hardline products one from amazon.

              This is whole thing is a little disappointing with respect to my break in period - I was under half throttle as instructed but well over the prescribed 3k rpm for a lot of the break in. I hope break-in engine loading has a greater influence than engine rpm on future longevity.

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              • #8
                Since you have a siamese coil, it's 2 pulses per revolution. Remember that both cylinders fire during compression, and they both fire on exhaust. And each plug wire sees the same signal. So each compression gives 2 pulses, and each exhaust also gives 2 pulses.

                As for break-in, the thing is to allow bearings to mate, and rings to seat. After about 2 hours, the bearings are pretty good. Then you have to "run it like you stole it" while as warm as possible (with 10w-30 oil -- not over filled by even a drop) to seat the rings. You should be OK.
                Paul
                Buffalo NY USA

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                • #9
                  Yep, induction tach must be set to 2 pulses per revolution in order to read correct rpm throughtout the whole rpm range. Portable OB's delivered with a prop are usually medium pitched ones. Doesn't mean that that's the ideal prop for your combo, after break end period ends will need to go for a prop maximization.

                  Ideal is to prop your OB right with a less prop pitch ir order to rev at max 6 K wot rpm range when at full throttle. Report the max wot rpm achieved as loaded to start propping it right.

                  Correct OB height, trim and deck weight distribution is a must have to get the max fun out of any underpowered portable OB.

                  Happy Boating


                  Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

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                  • #10
                    A siamese coil fires once each revolution !!-------And one spark on each plug every revolution-------On one cylinder it fires properly on compression.-----On the other cylinder the spark does nothing as it is the exhaust stroke.

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                    • #11
                      Originally posted by racerone View Post
                      A siamese coil fires once each revolution !!-------And one spark on each plug every revolution-------On one cylinder it fires properly on compression.-----On the other cylinder the spark does nothing as it is the exhaust stroke.
                      No. Since it's a 2-cylinder, both plugs fire twice each revolution. One is after compression, while the other is on exhaust.
                      Paul
                      Buffalo NY USA

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                      • #12
                        I do not think so---------It is a 4 stroke and therefor 2 revolutions to complete the cycle.------Therefor each sparkplug fires every ONE revolution !!!-----Think it trough mate.

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                        • #13
                          OP needs to test the induction tach set to 1 and 2 sparks per revolution to determine which setting reads max wot rpm range around 5/5.5K K rpm. My vote is for 2 sparks per revolution as stated by Paul.

                          Happy Boating


                          Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

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                          • #14
                            Each sparkplug fires once per revolution of the crankshaft !!!-----Both plugs fire at the same time.-----One spark plug does some good and ignites the mixture.-----Other cylinder sparkplug fires on exhaust stroke.----AKA a " wasted spark " system.

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                            • #15
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                              Originally posted by racerone View Post
                              Each sparkplug fires once per revolution of the crankshaft !!!-----Both plugs fire at the same time.-----One spark plug does some good and ignites the mixture.-----Other cylinder sparkplug fires on exhaust stroke.----AKA a " wasted spark " system.
                              Right. And since you are seeing both plug wires (siamese coil) you see two pulses per revolution. Just as though you were monitoring the wire from the CD to the coil.
                              Paul
                              Buffalo NY USA

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