For those of you yet to install a tach that dont want to pay 200 bucks for one, heres a 40 dollar alternative.

You can run a sunpro tach if you dissasemble it and replace R9 (resistor) with a 780K ohm resistor. Then set the selector switch to 4 cylinder (you just replaced the 4 cylinder resistor to work on your ds), and wire the tach input to the crank sensor pickup wire at the cdi box.

Not the best unit, Not the best setup, not water tight, but with a little clear silicone sealer applied carefully, its splash proof and only 35 bucks. I've done it to both size sunpro tachs. Only bad thing is there only 8000 RPM tachs......

But if your cheep like me, 40 bucks is easier to stomach.......

They come in the larger 3 1/2 inch (i think thats the size) and a smaller 2 5/8". Dont presure wash or hose it directly and your fine to 8000rpm. More Rpm wont hurt it, but it might start spinning at 10,000 untill you back off of the gas and drop below 9000 rpm.

If you have acces to a function generator, you can calibrate it while your in there. Set the function generator to 133.3 Hz and turn the trim pot in the tach till it reads 8000 rpm. If you use a 2% tolerance 780K resistor, you shouldnt have to make any adjustments.

Not as easy as pluging in the bombardier unit, but might save you 150 bucks?

Dave.

 

berksglh, thanks for the info on the tach. If I can't get a new ring for my stock tach (from wrecks) then I might look @ doing that instead of buying a new one.

 

Excellent info! I suppose this should be helpful for any atv?

 

i have a digital "tiny tach" that came out of a cabelas (i beleive) catalog awhile back....

it shows hours/minutes it has run and current RPM

its been sitting in my garage for a year (i got the BAJA ds so dont need two tachs)

not trying to make a for sale thread out of this but if anyone is interested in it send me a PM

 

Excellent information, thanks!! A cheap tach may be the way to equip a machine that's subject to abuse (MX, GNCC). Do you think it will work with one of their 10K rpm tachs?

 

Supposedly in early summer Trail Tech is releasing a tach/egt/speedo (I think but it might be something else) in an all-in-one unit like their computer. And to top it off target price is $100.[img]i/expressions/face-icon-small-happy.gif[/img]

 

Yes and no.... R9 on the other boards may not be the same value to start with, and the counter chip on the board may be different and need a different value to calibraate to the 1 cylinder tach input.

The process is simple, but some knowledge and tools are required, or its basically imposible. If you can dissasemble the tach, study the cylinder selector switch. The is most likely a common pin and 3 selectable pin based on switch position. In the 8K tach i have these 3 pins corespond to one of 3 resistors. Each resistor value is selected for the number of ignition pulses per revolution.

The DS650 Crank sensor fires 1 time per revolution, 8000 RPM is 8000 Pulses per minute, divide by 60 seconds in a minutem and you get 133.33 pulses per second (Or a frequiency of 133.33 Hertz) The actual coil signal most likely sparks on the exhaust stroke as well as the power stroke as the CDI box cant tell what stroke the the cam shaft is on. It only can tell when the crank is just about to TDC. Otherwise the Frequience to calibrate the tach to would be cut in half if.

I conected whats called a decade box (switch selectable box to simulate any resistor value you want) in place of the resistor comming of the switch i deturmined was the 4 cylinder resistor (or what ever one is easiest to get at, just set the switch for the one you are replacing) I set the decade box to the resistor value i was replacing, this is just a starting point. Then I connected a functin generator to the tach input, (function generator simulates in this case the pulse input from the crank sensor, or rpm) Applied 12 volts to the power wires and Set teh generator for 133.33 Hz.

The started changing the resistor value one way or the other till the tach read 8000 rpm. It read 4000 before making adjustments as a 4 cylinder automotive motor sparks 2 times per revoloution.

I did a simmilar tach mod 9 years ago on my 1985 SP600 single cylinder 4 stroke dirtbike. I dont recall the tach manufacture, but i toubt it was the same? That time i did it on the bike but had an inductive pickup tach hooked up to tell me what rpm teh motor was at adn set the tach resistor at idle whil on the bike. The reved it a bit to see if it was close.

I also killed one tach in teh process of figuring this out. That cost me 35 bucks. Disconect the 12 volts and the tach input before deslodering the resistor. I got sloppy on the last one and blew it up. But it was still cheeper then 210 bucks in teh end.

So yes and no.

 

Thanks. I understand what you did but I don't have the test equipment to tune a 10K unit. I'm still thinking about a separate EGT and Tach vs. a combo unit.

 

berksglh I got a sunpro off ebay and don't know which wires go to what.
Can you help

 

Black to a good ground,

red to a switched hot wire. (i tied red to the dead wire on the keyswitch, when the key was off, there is not 12V on it. )

The white wire runs the gauge light, i just tied mine in with the red.

The green wire is the tach signal wire.. It normally goes to the primary side of the ignition coil, but these tachs dont work like the ones made for the ds. I conected my green wire to the crank sensor ignition pickup. That wire runs to the CDI box as the ignition input signal. I conected the green wire just before the CDI box conector.

I would have to look in the manual or at my quad to tell you exactly what wire it is.

I can look and let you know friday if you need the info.

Also my origonal large sunpro tach vibrated a bit due to the plastic dash bolted solid to the frame. Was sortof hard ro read while riding, but gave you the idea. I am running the smaller unit now so i can fit more gauges in my oversized dash, and i now added the vibration Isolaters like the Baha X has on its dash, i saw at our local dealer. I made my own isolators out of radiator hose rubber, and blind nuts.

Tach is easy to read, and all gauges are stable while riding now.

Dave.......