Honda BF90 Tachometer Readings

G

Grazer

New member
Hi all,
This came up a few times last year and again this weekend. The Tach shows normal ranges for RPM one day and the next day the RPM needle goes off the gauge beyond 7000 before even up on plane. The motor and throttle response seem the same, but the tachometer is way off. Anyone else experience this and may know what is causing this?

Thanks,
Grazer
 
I've encountered this a couple of times a few years back. As I recall, there is a slider switch on the back that is used to select the number of cylinders for your engine. That can get dislodged or perhaps get corrosion on the contacts. I would cycle it a few times, make sure that it's on 4 cylinders, then check it again.

Remember, I'm running on old memory, so apologies if this isn't the issue/fix
 
As Steve says--the tach runs off the electrical impulses from an "alternator"--in the Honda case, I believe this is actually part of the flywheel--and might be more accurately classified as a generator--but the idea is the same--and if that switch is not making good contacts or there is a loose connection, it would be easy to get a multiple of the actual RPM.

Double check all spade connectors on the back of the tach--and even in the multi plug connector from the engine. I like to put a little contact cleaner on the spades, wiggle them around , and then put a drop or two of one of the water proofing agents on the outside.
 
Had sort of the same issues as stated, then after tapping on the glass it would correct itself. This went on for several trips then it quit working altogether. It would read correctly then have a surge or read well under the real rpms, I have just learned to drive by feel and will replace it soon. Why the units go out is beyond me but it sounds like yours is starting to fail. The only suggestion I can make is to check your wiring to see that all connections are tight and corrosion free.

Dan
 
Grazer,
My tach has been doing the same thing for the last few hundred hours. I tap on the glass and then the gauge reads normal. I'm getting ready to roll over 1000 hours and plan to order and change that tach at that point. I will need Honda tachometer 37250-ZW5-010ZA (tach plus hours gauge for about $100 dollars from boats.net)
Best regards,
Steve Baum
 
My 90hp Honda did that same thing 10 yrs ago. A tap on the glass would "settle it down" for awhile then do it again.
Dr. Bob's solution worked for me and is still working 10yrs later.
Now my 200hp Honda is doing the same thing. I am at the glass taping stage with it and so far so good. Will do the spade terminal clean thing soon.
It must be a short-coming in the design of those tachs.

I just replaced my Honda water pressure gauge. Got it from Amazon. It is exactly like the Honda gauge except it was manuf. by FARIA. Works great. 25lbs. at 4000 rpm's.
After examining the old gauge it was manuf. by FARIA also. I think it got "buggered up" by salt water.
 
On our last trip out, I had to start tapping on the Honda voltage gauges. They would work for a while, then show low voltage, or nothing at all. Separate volt reading on the Navman indicated that voltage was good. Tap -tap- tap on the Honda gauges and all was back to normal for a while. Haven't checked the terminals yet...
 
It's a beautiful thing, Jack. Spent the 4th of July weekend out in PWS with the nephews. Plenty of room for everybody. Caught a bunch of reds, a halibut, and topped it off with a few gallons of shrimp to break her in right. Wife loves the hot water, stand up shower, and flushing head. Think we're gonna keep this one for a while. :mrgreen:

(We even towed a disabled 22-foot boat from Upper Herring Bay across Knight passage to Main Bay where we were relieved by the Coasties. Wouldn't have even attempted that with the 17-foot Arima...)
 
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