Using Automotive Style Tach? Is It possible...

[xj11yamaha]

hey there everyone, i have a SunPro Automotive
Style tachometer, would it be possible to hook it up too the tach output wire that is on the bike harness itself, you probably know why i ned to know this, if youv'e seen my project.... i really dont want to spend anymore than i have to on parts and since i already have a tach i was wondering if i could use it.... I wonder if it would damage the tach if i tryed it? Thanks

heres a link to me xj1100/ golf cart project if you havent seen it yet!
XJ1100J Maxim Golf Cart Project

[Dennyz]

The problem is that the XS fires two cylinder at the same time, twice. Each coil fires every 360 degrees of crank rotation and the two coil are 180 degress apart. That is the reason for only two coils on a 4 cylinder motor. That is also why the XS tach runs off the generator. An automotive tach expects a sequence of firing pulses, one for each cylinder.

It is possible to build a simple circuit that would sample the coil pulses and generate the sequence of 4 firing pulses. Logically and'ing (digital speak) the two pickup coil outputs together.

This is kind of related to one of my back burner projects to convert an XS over to 4 individual coils. One day I was looking at the distributorless ignition on my '00 Chevy truck and thought "What if!". It would end up being a total replacement of the XS ignition system.

[Dennyz]

I doubt it would hurt the automtive tach to hook it up. However, with the tach switched to 4 cylinder and connected to either of the coil pickups, it would read half speed. If the tach has a 2 cylinder mode, that would work.

[xj11yamaha]

well hey do you know what would be involved in making that circuit, could you maybe help me on this one, becuase i really like the xj's original tach but "Ching, Ching" there comes the moeny factor and im going to use the same style gauges for the whole dashboard..so.... If you wouldnt mind helping me design a circuit or something it would be very apprciated! Thanks!

By the way i don have some elecrical knowledgde, i can solder, and i have made my own wiring harness, etc etc. im not the greatest at advanced-circutry though thats my only real electrical weakness, i can wire you up a 3500 Watt Component and sub system in your car but when it somes to circuit boards count me out.

[Dennyz]

I will take a shot at it and see what I come up with. I think I can do it with a couple of inexpensive transistors and few resitors, all available from Radio Shack.

What is your time line on this (how soon do you need it)?

[xj11yamaha]

oh wow! Thanks but, you dont have your own money on it! I dont need one for a while, proably around the end of october is when i'll have the actual engine done and start working on the other misc. stuff like gauges etc. Thanks! Let me know if you want me to send a few bucks or something to get the parts. Or i can buy the stuff after your done to cover your expenses. Thanks Again!

[macnut xj]

I happen to have a couple of extra XJ guage clusters laying around after putting eXJunk back together. I could make you a good deal on a tach from one of them.
LMK

[xj11yamaha]

yeah i would probably purchase one from you if the price is right, i know you need to make some money too, i'm stretching the budget far and wide right now, see i'm still in high school trying to pay for the car mods and the golf cart project at the same time, so if youv'e got one ill more than likely buy one but maybe sometime later in october or november, but now i gotta proritize i gotta find a older atv shaft driven rearend with the brakes, swingarm shocks, and the shaft for the golf cart! So sure ill probly take one depending on the price thanks for the offer!

[macnut xj]

No problem. When you're ready let me know. I'm not really worried about making money on spare parts. If I did, I'd put this stuff on eBay! Heck, I lost my job back in January and I'm trying to get my own business going, so I feel your pain. My eXJunk is down right now while I save up the money for new needles and seats for the carbs......