Tachometer or speedometer

[PISTONESAL]

Hello,

I have 2 look like speedometers on my boat when I got it. First, neither one is hooked up. What/how do I hook it up? Also, will I be able to use one of them to help aid in doing an idle rpm test? I'd hate to go out and buy a $75.00 tachometer if I can use one of these. Can someone please help? I don't know how they work. any help would be greatly appreciated..

thanks

Sal

 

[Theoutdoorsman]

Re: Tachometer or speedometer

The speedometer is one of the least useful tools to a boater, in my opinion. Once you know how fast it will go, it is what it is. It would be in your best interest to invest your money in a good tach so that you can monitor your rpm's and prop the outboard accordingly. My speedometer is merely a hole filler. I could never get the pickup tube to stay down in the water so I put it in the inside of the boat transom and got rid of the problem........ ...... Needless to say, I don't use it anymore. If you want to know how fast it will go, get a friend to gps the rig at WOT and forget about it. It's unimportant anyhow. The WOT and idle rpm's, on the other hand, are.

 

[Joe Reeves]

Re: Tachometer or speedometer

As above, the tachometer is most important.

However, a speedometer in conjunction with a tachometer can be rewarding as follows.

If you have a engine where the top rated rpm is say 6000 rpm, and you have a propeller installed that at full throttle reads say 5800 rpm, that's a good match pertaining to engine/propeller.

Now, under way, at say 5200 rpm, the speedometer reads (to pick a figure) 40 mph, and at 5800 rpm the speedometer still reads 40 mph (due to the hull configuration), you are wasting gasoline and it would be advisable to back the engine down to that 5200 rpm figure to conserve fuel.

 

[Fireman431]

Re: Tachometer or speedometer

Make sure the tach works. Should be hooked to the engine wiring harness (you didn't specify make/model of engine or boat). It reads with a +battery feed for the ignition switch or harness, a -battery ground, a coil feed (usually green), and a white wire for the inside light. There are usually adjustments on the back of the tach to specify the number of cylinders in the engine. Make sure that is set correctly.

Notwithstanding the speed and fuel use, you want to be sure you're not over-revving the engine, which could lead to higher costs than the fuel.

The speedometer is usually just a pitot gauge mounted on the transom (connected with a long lenght of vacuum tubing) or mounted in the lower unit of the engine itself.

Good luck!

 

[PISTONESAL]

Re: Tachometer or speedometer

Thanks for the replys. I have a Bayliner classic with a 1978 Johnson 75HP outboard.. What is the coil feed? Is it possible to pickup a tach not to expensive? I was planning to get this going this weekend but I need a tach. Can one be picked up at a auto store or does it have to be special since it is marine?

thanks

sal

 

[ezeke]

Re: Tachometer or speedometer

If your boat is equiped with a side mount remote control, it may have a plug located below the ignition switch for the tachometer harness. If so, you might be better served by buying the tachometer with the harness from a OMC/BRP dealer.

Otherwise, any marine tachometer that fits the hole in your console and can be set to 6P should serve you well.

The OMC wiring colors are light blue for the positive lighting, black for ground from the ignition switch, purple for positive voltage from the ignition switch, gray for the signal from the engine.

 

[jay_merrill]

Re: Tachometer or speedometer

There are usually adjustments on the back of the tach to specify the number of cylinders in the engine. Make sure that is set correctly.

Just a minor correction because I wouldn't want the OP to become confused - the tach is set for a given engine according to the number of "pulses," not cylinders. This is a function of the number of alternator poles and is normally set at half the number of those poles.

Just to make things easy, though, the OP can identify the year/make/model of his motor and you can pretty much bet someone around here will know how many pulses to set the tach for.

 

[Fireman431]

Re: Tachometer or speedometer

Thank you for the correction. I know my Johnson 150 tach has 4/6/8 on the back and I assumed that was cylinders (as mine is set on 6). Maybe that's why mine reads 9,000 RPM at idle.....

 

[PISTONESAL]

Re: Tachometer or speedometer

My motor is a 1978 Johnson 75HP. What is my pulse count?

Thanks

Sal

 

[ezeke]

Re: Tachometer or speedometer

6P on Teleflex and OMC/BRP Tachometers. See page 4 for application chart: http://ww2.tflx.com/PDF/99320.pdf


Faria does not have the 6P setting on all of their tachometers, just the system check ones.

 

[PISTONESAL]

Re: Tachometer or speedometer

What about a tiny tach model TT2262XLR?

 

[Reggie08]

Re: Tachometer or speedometer

6P on Teleflex and OMC/BRP Tachometers. See page 4 for application chart: http://ww2.tflx.com/PDF/99320.pdf


Faria does not have the 6P setting on all of their tachometers, just the system check ones.

My Faria tach has a 6P setting without the system check, but the reading seems to be a bit high on it so it may not be the correct tach. Picked up the tach, voltmeter and trim gauge for $40 off ebay.

 

[ezeke]

Re: Tachometer or speedometer

Try to stay up to speed on this stuff. The newer non-systemcheck Faria tachometers do not have 'p' settings per se. You set it for 5 for the equivalent because there is no 6. Here is a link to their application chart:

http://faria-instruments.com/site_manuals/IS0012u.pdf

Note the two windows in the lower right corner for the possible settings.

 

[Reggie08]

Re: Tachometer or speedometer

Son of a....my tach is a 6000rpm tach which according to that application chart is for I/O motors only

 

[ezeke]

Re: Tachometer or speedometer

Yes, but, then the last line in the 6000 RPM window says 12 pole outboards can be set on 4.

 

[Reggie08]

Re: Tachometer or speedometer

I noticed that too. I'll change it to 4 and see how it reacts. I thought it was little off yesterday when I bumped the throttled to WO and the tach maxed out.