Honda Tachometer BF90 - Question

Montana Kev · Posted: Tue Aug 30, 2011 12:28 pm Post subject: Honda Tachometer BF90 - Question

We repowered the recently purchased 1998 22 with a 2003 BF90 (it came with a Honda 50). The tachometer reads about 600 rpm low. There are no adjustments on the Honda tachometer for the different size engines/more cylinders. A Honda dealer just told me that the old tach needs to be replaced with one specifically for the 90HP.

So, I wanted to check with the group on recommendations for a new/used tach. What would be a good replacement, type, brand, where to buy. Maybe someone has a used one for sell etc…

Thanks,
Kevin

Wandering Sagebrush · Posted: Tue Aug 30, 2011 12:53 pm Post subject:

Kevin, that surprises me that there are no cylinder settings on the back of your tach. Both of my boats that had BF90s were rigged with Honda tachs that had a slider switch on the back for the number of cylinders.

That said, I think these tachs are of poor quality. More than once, I have had them read significantly off actual RPM. At one time, I thought I had a slipped prop, but it was just the tach reading high. Maybe the newer instruments are of higher quality, but I would look for a third party tach that has good reviews (if there is such a thing).

TOGO · Posted: Tue Aug 30, 2011 12:56 pm Post subject: Tack

On the Bartender I built I had a 2005 Honda 50 with a Honda Tack on the back there were little switches that allowed one to set the tack up for different number of cylinders. I just looked at my 2008 Honda 90 tack and can't tell with out removing it. Try looking at the Honda site for the tack and see if it is adjustable I bet it is.

Montana Kev · Posted: Tue Aug 30, 2011 1:15 pm Post subject:

jlastofka · Posted: Tue Aug 30, 2011 3:46 pm Post subject:

If your tach is off by a constant ratio, it could be a number-of-cylinders setting. If it's off a nearly constant fixed amount, it's some other problem. Example: Going from a 4 to 6 cylinder setting at 5000 RPM should change the tach from 5000 to (5000*4/6=) 3300.

I have a newer V-Tec 90 Honda and the tach sometimes reads way off. I can often tap on the glass window and get it to jump to a reading that's probably correct. It seems kinda bogus (and surprising, coming from Honda) but I've heard similar things from others. It doesn't seem like a sticky needle, judging by the way it moves around. It just seems way off, and then it can be coaxed into reading properly. This only happens once in a while.

I expect there are inexpensive tachometers from automotive places like JC Whitney (if they're still around) and I believe all the newer outboards have a tachometer output signal you can tap into. I think some of the tachs will take their input from the engine alternator also.

I'm installing a Flo-Scan fuel totalizer and it includes a digital tach, so I'll have an exact reading from that. Not that I really care. I want the GPH or MPG readings to play with trim tab settings and boat weight distribution.

Even heavily loaded and tail heavy, I think I remember getting around 3.3 mpg at Lake Powell at 15 or 17 mph, so I guess the boat was doing OK and I don't expect to save enough money to pay for the fuel gage. I just like data and experimenting. So I'll recover some money, and have fun experimenting, and have increased range.

Les Lampman

Montana Kev · Posted: Tue Aug 30, 2011 9:19 pm Post subject:

Thanks Les, that solves the Tachometer Mystery. I will scout for a new one, probably just get a basic Teleflex. Someone should be able to put the one I have to good use on a Honda 50.

Thanks to all that responded.

Kevin

Gilbertsons · Posted: Sun May 17, 2015 11:59 am Post subject:

I would like to restart this discussion for those motor heads out there. I have had the same problem described in this thread. I have a 2008 BF-90D Honda Outboard with EFI. My tachometer consistently reads RPM's below what the motor is actually running at. I have read the related threads and have cleaned contacts etc. I think it may be related to the "turn" setting on the back on the tachometer. My tachometer options settings are as follows:

Pole Setting
4 1
6 2
10 3
12 5

My current setting is "2" meaning it is set for "6" pole. What is confusing to me is that many of C-Brats comments on this is that you set it for the number of cylinders on the motor. In my case that would be setting "1" for 4 cylinders. But I really think this would be the number of poles on the ALTERNATOR, right? I think my alternator for this year motor is 44 amps, but I don't know that number of poles on it.

Does anyone know?

I hoping it it's 4, so I need to have my setting on "1" and then maybe my tach would read at a higher range. I would have experiemented with this settings if I had the boat in the water and not stored on the trailer!

Jack in Alaska · Posted: Sun May 17, 2015 8:05 pm Post subject: 90 tach

On my previous 22' I had a Honda 90. The tach on it worked well for 5 yrs. then started to get "funny". It would go up and down w/o the engine changing. A good hard slap with my hand would return it to the proper RPM. It still does that but basically works ok. Not a 1st class item.

journey on · Posted: Sun May 17, 2015 8:07 pm Post subject:

Journey On has a Honda tachometer and it's not the best in the world. There are times I darn near break my finger, hitting the glass before it settles down and reads right. Why don't I replace it? Lethargy, hitting it is less work than replacing it, and cheaper. This year it's going to get replaced.

The switch on the rear is for cylinders, of which the Honda BF-90D has 4 ea. Diesels use the alternators to run any electrical tach, gas counts the cylinders.

Boris

tsturm · Posted: Mon May 18, 2015 10:24 pm Post subject:

Les Lampman · Posted: Tue May 19, 2015 1:02 pm Post subject:

The BF90 has a 4-pole tach.

Les

Les Lampman · Posted: Tue May 19, 2015 1:14 pm Post subject:

By the way, there is no such thing as a "Honda" tachometer unless you have an early BF35/40/45/50 (early to mid 90's).

All other gauges are sourced through American Honda Motor Company (not Honda of Japan) and were/are made by Faria, Beede, VDO, and Veethree. We've always had at least two choices in the accessory catalog to pick from. We had trouble with Faria right from the start, so we always used Beede gauges until they were no longer available. Now we use Veethree and they seem to be doing well.

Les

rainger · Posted: Tue May 19, 2015 8:37 pm Post subject:

Like others said the tachs are adjustable. I have the same tachs as you I bet. Here are pictures of the front and back. As others have said you change the little screw to different locations for proper readings.

[1mg]http://www.c-brats.com/modules.php?set_albumName=C-Hawk&id=20150504_130723&op=modload&name=gallery&file=index&include=view_photo.php[/img]

[img]http://www.c-brats.com/modules.php?set_albumName=C-Hawk&id=20150504_131413&op=modload&name=gallery&file=index&include=view_photo.php[/img]

Heck I cant get the image to inset into the message even when it is in my album.

Les Lampman · Posted: Wed May 20, 2015 1:19 pm Post subject:

Hmmm, I need to slow down when I type!!!!

The BF90 has a 4-pole alternator (not tach as I typed).