Small Outboard Tachometer

[kestrel452]

Hi all,

I just picked up a 2000 Mercury 2-Stroke 15HP outboard, which has a charging/electric start kit and tiller installed. It's going on a 3.5m Zodiac hard floor inflatable. I'd like to build a miniature instrument panel for it. I'd like to at least have a tach, and a water temp gauge to ensure the engine is getting enough water and isn't overheating. Is there any way to connect a round, needle dial tach and temp gauge to this engine? If not, im thinking I'll just use a Trail Tech Tach-Hour portable tachometer to at least make sure that it's propped right for my boat.

 

[alldodge]

Hi all,

I just picked up a 2000 Mercury 2-Stroke 15HP outboard, which has a charging/electric start kit and tiller installed. It's going on a 3.5m Zodiac hard floor inflatable. I'd like to build a miniature instrument panel for it. I'd like to at least have a tach, and a water temp gauge to ensure the engine is getting enough water and isn't overheating. Is there any way to connect a round, needle dial tach and temp gauge to this engine? If not, im thinking I'll just use a Trail Tech Tach-Hour portable tachometer to at least make sure that it's propped right for my boat.

:welcome: to iboats

There is always a way, just depends on how far you want to go to do it. Can mount a plate on the outside of the cover, or do you want to cut holes in it? Where would you like to have it installed?

 

[achris]

Standard marine tachos pickup signal from one of the AC legs of the rectifier. Don't bother with a temp gauge, get a water pressure gauge...

Chris......

 

[kestrel452]

Standard marine tachos pickup signal from one of the AC legs of the rectifier. Don't bother with a temp gauge, get a water pressure gauge...

Chris......

Water pressure seems like a good idea. How do I go about driving a gauge from an outboard like that though?

 

[achris]

Buy a water pressure gauge kit. It will come with a fitting for the engine powerhead, in the water jacket somewhere. Usually you'll find a plug in the engine. The kit also comes with a length of thin tubing and the gauge itself... Be careful, there are usually two ranges, 0 to 15 psi and 2-30 psi. Make sure you get the right gauge for your engine. The seller should have a chart with all the engines on it and it shows which gauge to use.

Merc gauge kits for water pressure are like this one -> http://www.ebay.com/itm/Mercury-79-15128A4-psi-gauge-kit-/221585039823

Chris.........

 

[gm280]

Almost any marine tach can be setup to be used. And other then a pee tube outlet, what other information do you need to determine your engine is working properly. A water pressure gauge will only show the pressure but certainly not show proper water flow through your engine. A plugged outlet or any other blocked or partially block water passage will still show pressure... I like to also know about my engine's performance but real knowledge and not some feel good info. I went through the exact same ideas when I bought my new Bass Boat some years ago. I wanted every conceivable gauge known to man to keep me totally informed about any issues that could possibly show up. And after putting such gauges in the dash, I found out I relied on them near about zero... And in less that one year later, I hardly even watch any gauge but tach and the pee tube stream. So it is your setup and everybody has their own ideas! Certainly nothing wrong with that, but there is no perfect gauge to let you know everything is working perfectly... I just hate to see you go through so much effort and then realize what you thought was a good setup really doesn't provide mush of any additional safeguards. But this is just my .02 cents worth!

 

[kestrel452]

I'm almost certain I already know the answer to this, but is there any way to tune this engine to safely gain a few more horses?

 

[Silvertip]

If there was a way to boost the power with no ill effects, the factory would have done so and called it a 20 HP rather than a 15.

 

[kestrel452]

If there was a way to boost the power with no ill effects, the factory would have done so and called it a 20 HP rather than a 15.

Well, they actually do. For example, the current 15HP is just a tuned down version of the 20HP. A simple change in the porting and exhaust yields that extra 5 horses, same engine otherwise.

 

[achris]

Well, they actually do. For example, the current 15HP is just a tuned down version of the 20HP. A simple change in the porting and exhaust yields that extra 5 horses, same engine otherwise.

Urrrr, are you SURE?????

The 15hp is the highest horsepower of that engine family (262cc). The 20hp (400cc) is a completely different engine...

Chris.....
(I was a Merc dealer in the 90's and am quite intimate with the small engine families) .

 

[kestrel452]

Urrrr, are you SURE?????

The 15hp is the highest horsepower of that engine family (262cc). The 20hp (400cc) is a completely different engine...

Chris.....
(I was a Merc dealer in the 90's and am quite intimate with the small engine families) .

Emphasis on the word *current*. The current 15 is indeed a down-tuned 20, both are essentially the same 114lb package from Mercury, but of course since you can't buy the 2-strokes anymore these numbers are for the modern 4-strokes.

While you're right in regards to the older 2-strokes, the 15 and 20 came in different chassis (hence why I didn't think it was likely to be able to up-tune a 2S 15), my inflatable is rated for a max 20HP. I would've bought an actual 20, but they're just too damned heavy to sling around by hand (i don't have a trailer). The 2S 15 actually weighs less than the 4S 9.9. I was just hopeful there was some way to get a little extra power out the relatively lightweight package of this engine, because Tohatsu who seems to be making everyone's powerheads these days makes an 18hp 2S in the same size/weight as the Merc 15.

 

[achris]

It may involve a change of carb (usually does for most engine changes. It's the majot difference between the 75hp and 90hp 3 cylinder 2S) and maybe some different porting of the block. I know the 9.9hp and 15hp Johnsons had different exhaust 'megafons')

That all said, you're not likely to see much change in performance with the same engine block. What you need is more capacity, it's mostly about low and mid range torque, not top end HP....

Chris....

 

[gm280]

Seem so many what to "tune" their engine for more power. And nobody yet as come up with a viable answer. The easiest way to do that is to unbolt your present engine, and bolt on a bigger engine. That seriously is the cheapest and best option...

 

[achris]

Seem so many what to "tune" their engine for more power. And nobody yet as come up with a viable answer. The easiest way to do that is to unbolt your present engine, and bolt on a bigger engine. That seriously is the cheapest and best option...

100% correct, and the only answer I give when asked that question....

 

[kestrel452]

I called Speedhut and Auto Gauge. They were unsure which gauge would work, the type that attaches to the negative side of the ignition coil or the W or R terminal on the alternator. No idea what to tell them....

 

[kestrel452]

Another question if you guys don't mind...

The electric start kit and charging kit, does it add a standalone alternator or does it just modify the magneto to allow the excess power it generates be used to charge a battery? How many amps does the charging kit on this motor put out?

 

[achris]

I called Speedhut and Auto Gauge. They were unsure which gauge would work, the type that attaches to the negative side of the ignition coil or the W or R terminal on the alternator. No idea what to tell them....

Outboards don't use a coil fired system, usually because outboards have a single coil per cylinder. They generally use one of the AC legs from the alternator. Most are 12 pole alternators and marine tachos are designed to use this pulse.

Another question if you guys don't mind...

The electric start kit and charging kit, does it add a standalone alternator or does it just modify the magneto to allow the excess power it generates be used to charge a battery? How many amps does the charging kit on this motor put out?

Yes, they have an alternator coil under the flywheel. Some are integrated with the exicter windings for the power pack(s), but electrically, it's isolated.

Chris.......

 

[kestrel452]

Yes, they have an alternator coil under the flywheel. Some are integrated with the exicter windings for the power pack(s), but electrically, it's isolated.

Chris.......

So I take it Mercury sold these outboards all with the same stator but the ring of coil windings (if that's even what they're called) was somewhat incomplete unless the "aux stator" was installed to fill the gap? It's interesting how only 3 coils (a 1/8th section of the stator ring) that's isolated can produce power, i always thought it had to be a complete ring.

I read on another forum that if you don't have a battery hooked up to the charging cables you'll fry the rectifier. But that doesn't make sense because then you'd fry it with a fully charged battery too, and nothing to charge means no current flowing which means no heat....

 

[achris]

So I take it Mercury sold these outboards all with the same stator but the ring of coil windings (if that's even what they're called) was somewhat incomplete unless the "aux stator" was installed to fill the gap? It's interesting how only 3 coils (a 1/8th section of the stator ring) that's isolated can produce power, i always thought it had to be a complete ring.

Correct. You only need a magentic field passing over a winding of wire to induce a current flow, so no, the coil doesn't have to be a complete ring.

I read on another forum that if you don't have a battery hooked up to the charging cables you'll fry the rectifier. But that doesn't make sense because then you'd fry it with a fully charged battery too, and nothing to charge means no current flowing which means no heat....

Unless the 'rectifier' is also a regulator, then yes, no battery could easily lead to damage.... But a straight rectifier, no damage. As long as the voltage rating of the diodes (that make up a recitfier) are in excess of the peak voltage the alternator winding is capable of producing without load....

Chris......

 

[kestrel452]

Unless the 'rectifier' is also a regulator, then yes, no battery could easily lead to damage.... But a straight rectifier, no damage. As long as the voltage rating of the diodes (that make up a recitfier) are in excess of the peak voltage the alternator winding is capable of producing without load....

Chris......

The way you're explaining this is a little above my own comprehension

Are these charging kits made by Mercury (at least for my motor) able to be operated with no battery attached? My inclination is to say yes since the electric start and charging kit were sold separately but then again I dont know the difference between rectifier/regulator and straight rectifier systems. Thank you for answering my questions so far Chris!