Since you have never been able to get it up to maximum rpm, it does sound like it's over pitched.
If your engine speed is now lower than before, it might be your filters. I use a 10 micron primary, and a 2 micron secondary. You might also make sure all your fuel lines are tight, and that you're not sucking air along with fuel. Alan Bergen 35 Mk III Thirsty Rose City YC Portland, OR On Sun, Sep 29, 2019 at 11:53 AM Bruce Whitmore via CnC-List < cnc-list@cnc-list.com> wrote: > Hello all, > > We have a 1994 C&C37/40+ with a Yanmar 3JH2E engine. Without load, it > will rev to the 3600 - 3800 range. I have checked the tachometer using a > handheld electronic unit, and it is generally accurate (I think within > about 50 rpm). > > The transmission is a Kanzaki KBW10 with a gear ratio of 2.14. Historically, > I have never been able to get the engine above 3200 rpms, and I strongly > suspect the 3 blade fixed prop has too much pitch. Thus my recent > questions about switching to a folding/feathering prop. According to the > survey, the prop is a fixed, 3 blade 16 x 10 prop. > > A few months ago, I noticed upon running the engine at about 3000 rpm > thinking that running it about 85% of max would be best, it started running > rough when in gear and at low speeds. I added injector cleaner, replaced > the filters, and even went so far as to visually inspect the tank for > water, dirt, etc. That visual inspection showed a reasonably clean tank > (no evidence of water, a few black spots on the bottom, but they were very > well attached to tank, no loose particulate matter). At that time, I ran > quite a bit of fuel through the racor using a small 12 volt pump, using it > as a vacuum to suck up any fine dirt or water out of the tank. I found no > evidence of such in the racor bowl. > > Recently, the engine has become reluctant to go any faster than 2800 > rpms. The bottom is dove regularly, and though there are some minor nicks > in the prop according to the diver, they are nothing to worry about. The > engine still revs to full speed in neutral, does not smoke either white or > black regardless of the throttle position, and starts easily. The rough > running in gear has now gone away, and I credit that to the injector > cleaner. > > So, a few questions for the collective brain trust: > > 1). Do you think our boat is overpropped? What should the right prop be > if it were a fixed, 3 blade? > > 2). What would you expect is the reason the engine does not want to > acheive the 3200 rpm it used to, keeping in mind it is not smoking, > missing, or dying? > > Looking forward to your thoughts, > > Bruce Whitmore > 1994 C&C37/40+ > "Astralis" > _______________________________________________ > > Thanks everyone for supporting this list with your contributions. Each > and every one is greatly appreciated. If you want to support the list - > use PayPal to send contribution -- > https://urldefense.proofpoint.com/v2/url?u=https-3A__www.paypal.me_stumurray&d=DwICAg&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=9w3G7Cf8YfQnrjmtuNxwDJYr3JMv9f1pAfgAJ9xXYQQ&m=UiT3BPkbK6yBhQgGGEtnuY4Y6z-gNFXcOap8-twTjIE&s=x4iQewqMjgTN5WRC9hDZMAIaJg5bWQZgJI6sQeEEKJM&e= > >
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