honda tach adjustment or are my rpm's limited?

computer-rooter

I have just repowered my 22 classic with a 2002 honda bf90. It's claimed to have 20 hours on the powerhead, but that's another story. In the course of repowering, I also replaced the control console and cables, wiring harness, and added a complete set of honda gauges. Some of the crappiest quality instruments I've ever encountered in my life! Anyway, The tach is supposed to be set up according to the number of pickups (sensors) on the alternator. I've looked all over, and although I can't find the number documented, I think I see two pickups on the alternator. Assuming the alternator is that big spinny thingie under the plastic thing on top of the motor. My question is: Does anyone know the proper setting for that adjustment on the bottom of the honda tach to sync with the BF90A?

The reason for the above question is that when my tach settles down (it has a twitch -- is that normal?) and I can run WOT I can only get 4000rpm showing on the tach, for almost 25knots with a 3x13p honda prop. I dropped to the 13 from a 4x15 because at best trim and WOT I could only get 3800 showing on the tach and 28knots. I don't know if I have a bad tach or if the engine is limited somehow. It seems curious that I'd be going 28knots @3800 with that 15" prop. That would put me at about 40 or so at redline . . . which would explode the hull . . . It doesn't make sense.

Salty Dog · Posted: Mon Jul 10, 2006 8:56 am Post subject:

computer-rooter,
Had a similar problem on my Honda 75. The indicator dial on the back of the tachometer was set to the wrong position. Not sure if the 75 and 90 are the same (and I'm going from memory here), but I believe I had to change my setting to number 2, then everything worked fine. If you're totally unsure, just call a Honda dealer and ask them. That's how I figured mine out.

Jack

smittypaddler · Posted: Fri Jul 14, 2006 10:20 am Post subject:

I had the same concern on Na Waqa, and exactly the same symptoms; 4000 rpm wide-open, at 24 knots, with 13-pitch prop. I stopped at a Honda dealer in Florida. They told me the tach was for a different Honda engine, even though that's the way it came from the factory. I decided to make the mental adjustment, and left the tachs alone.

jennykatz · Posted: Fri Jul 14, 2006 10:58 am Post subject: tach problems?

I had Problems with a yami f115 The Tach had to be reset in the back just calll your Honda dealer he should be able to tell you what setting .
Also I have a 22 cruiser with a 06 suzi 90hp with a 14/18pitchs/s prop I reach 33mph at 5800rpm great suzi factory prop . your 13-15 pitch seems way to low call around at a prop shop and try diff pitches the17-19 seems like the best pitch for a 22 cruiser

Wefings · Posted: Fri Jul 14, 2006 12:13 pm Post subject:

Honda and Suzuki have totally different gear ratios [final drive ratio] . Suzukis turn much bigger pitch wheels at a slower speed than a Honda can .
13-15 inch is probably correct for Honda depending on load .
Marc

ccflyer · Posted: Fri Jul 14, 2006 12:38 pm Post subject:

If you check hondamarine.com, you can select the 90, and you'll be able to find performance tests with a C-Dory.

Seems the best performance was with a Honda 13 1/4 x 17 x3 or a Mercury 13 1/4 x 18 x 3.

computer-rooter · Posted: Fri Jul 14, 2006 4:05 pm Post subject:

I had started with a 15" 4-blade screw, thinking it was a starting point that I would either be going up or down from. I was getting a nice top end (28knots), but the tach was only reading 3800rpm. I went to the 13" 3-blade to see what would happen to my top-end RPM. I picked up 200, to 4,000rpm. However, I went down to 24knots and from an even 4mpg to about 3.4mpg.

That was when I began questioning my instruments rather than the motor. The tach takes a few minutes to settle in when I first start up, and often it remains in outlandish positions for a few miles before it settles in to anything that seems reasonable. For example, I know I'm not turning 8500rpm at 2knots. This is what it might show while I'm goign dead slow through the harbor. It may or may not return to where it was after I bump the trim.

I'm new to outboards. I don't know what they are supposed to sound like at a given RPM. I know people who can tell me within a couple hundred revs how fast their motor is turning over. I'm not one of them. So I have to rely on the gauges to tell me what's up. Being a pilot also, I've been brainwashed into trusting my instruments over my own senses. That works if I've got confidence in my instruments, but with a brand-new trim and tach gauge both acting funky, I've got no reason to trust them.

So, to give the new instruments a fair chance, I need to double check any settings and adjustments they require. Since the honda book and my local dealer are both silent on the topic, I thought I'd ask here.

. . .and I can't really ask the local honda boys any more questions. I had them do a checkout on this motor before I bought it, and do a 20-hour service. After 8 weeks, it came back with both the engine and lower end full of water (I drained close to 8 quarts of mocha out of the engine), tight valves, the old fuel filter, and the fuel lines reversed as to their direction of flow, which caused two carbs to flood and the other two to starve, and had fuel spewing everywhere. In my opinion these guys are dangerous and ought to be put out of my misery.