Re: [OMC-Boats] Engine RPM and Boat Speed

From: Don Mandelas <dmandelas@...>
Date: Mon, 28 Jul 2008 13:58:59 -0700

Ethan, I undertsand what your saying. I'll recheck the RPMs with the timing light again and double check the settings. (I'll re-do the test so that I'm confident with the results). Maybe I'll even get the tinytach you were talking about.
> Date: Mon, 28 Jul 2008 13:42:35 -0500> From: brodskye@...> To: omc-boats@...> Subject: Re: [OMC-Boats] Engine RPM and Boat Speed> > On Sun, 27 Jul 2008, Don Mandelas wrote:> > This weekend I was able to obtained a timing light and digitally measure> > the revalutions per minute of my V-6 155 hp boat engine.> > I discovered that when the timing light indicated 1,100 RPM's my boat> > tachometer was reading 1,000 RPM's. And, when the timing light indicated> > 4,000 RPM's my boat tachometer was reading 3,000 RPM's. This means my> > tachometer is reading a full 1,000 rpms below what it should be on the> > higher end of the scale and is probably the primary reason why I am going> > slower than normal. I'll replace the tachometer and try the boat again.> > This sounds a little strange - you say that the tach is reading low, so the> engine is actually spinning faster (and making more power) than believed.> > I found the opposite on mine - when I measure the RPM (using a TinyTach> inductive pick-up on a spark wire), I see that the tach is reading> substantially high (1000-1500 rpm). My understanding is that older tachs> tend to read high due to weakening of the return spring with age.> > Are you sure you had the timing light set properly (some can be switched> between various combinations of two-stroke/four-stroke, single/multi> cylinder, and wasted-spark modes) and it wasn't reading high by a factor of> two? I'm not sure how it works with older distributors, whether each spark> plug fires once for every revolution or just every second time. I think> it's the latter.> > Tinytachs are a fairly cheap way to have a more accurate RPM reading, as> well as an hour-meter. Unfortunately I don't remember whether the 4C or> the 2C should be used.>> > If anyone has figured out a way to adjust the factory OMC facts, I'd like> to fix mine. I haven't figured out how to do that yet.> > Ethan> > -- > Ethan Brodsky > _______________________________________________> OMC-Boats mailing list>>
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Received on Monday, 28 July 2008

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