Car tach on kz 700

Why the resistor trick works:

If you put 2 resistors of the same resistance rating (Ohms) in parallel, you effectively cut their total resistance in half.
If you put those same resistors in series, you effectively have doubled their total resistance.

Let's say you have 4 resistors, 10 Ohms each (to make the math easy). Each one of them individually are rated to handle only 1/4 Watt but you need a 10 Ohm, 1 Watt resistor. What to do?

You know that you can add the resistors together and their Wattage will increase by 1/4 Watt for every resistor you add. You got 4 of them but if you just string them together willy nilly, your total resistance will be wrong.

So, you take two of them and put them in parallel and get a 5 Ohm resistor rated at 1/2 Watt. Do that to the two others and now you have two 5 Ohm resistors each rated at 1/2 Watt.

Now, take these two resistor pairs and put them in series with each other and you now have effectively built a 5+5 Ohm, 1/2+1/2 Watt resistor which equals a 10 Ohm, 1 Watt resistor, voila!

The reason I was asking about the dwell time is if one of the coils is in dwell (meaning its negative post is connected to ground through the points or the transistor ignition so that the battery current is flowing through the coil), it is also forward biasing its associated diode meaning the diode is conducting (or on) thereby pulling the point that the tach sense line is connected to down to ground. This means all of the voltage drop will be across the resistors only and there will be virtually none at the sense point. This means the tach will never see a pulse as long as one of the diodes is "on".






Here's a great site that explains diodes:
www.allaboutcircuits.com/vol_3/chpt_3/1.html

If you guys are ever in I'll come on by and I will buy beer and we will bbq !! . All of this info was great. I have found a set up that does work its. Loud hvx last one I am running just like the pic

It is so nice to see it swing the right rpm thanks guys mabe we should put this in the file base just in case someone else needs it....

now that we have a combo that works is there anythig i should do to make it better or will it be ok the way it is.. thanks agen so you know there wasnt one person anywhere else who had a clue how to do this... thanks agen...

That's great. The best part is you get to say you made it, and it didn't cost $80.

Yes, there are a few things you will probably want to do.

You may want to just consider the first one a prototype.

That area of the bike gets a lot of vibration, so you will need to do something to make sure it all stays together.

I would get a single, 1 watt, 470 ohm resistor from ebay, if radio shack doesn't have them. Then put the 3 components (resistor and two diodes) into a W shape so all of the wires come out one way. Then heatshrink over each part. Then wrap them together with tape neatly. then I'd put one zip tie around the wires right as they come out of the bundle. This will make it a soft package where the wires take the brunt of the vibration rather than the components. Then I would zip tie the package somewhere to the frame near the coils.

The real problem is mounting the tach so it doesn't vibrate apart. I actually open up the Sunpro tach and silicone everything together, but make sure to not glue the moving parts. I find the frame for the needle movement usually needs some support or the vibration will make the needle simple fall off. (Of course, this is a much cheaper tach.) However, after doing all that, I've gotten 10 years out of this last one. (Previous ones only lasted 2 or 3 years.)