Snowmobile tach

[Kaptain Krunch]

Well i just got a sled for 5 bucks, no engine pretty much no rear end, but it has a tach, speedo, shocks, and a disk brake setup that looks like its on a 1 inch axle. Anyways i have some questions about the tach, how do i set it up, it appears to have 4 wires coming off of it. Im going to try and put it on a 100cc 4 stroke that hits 8k rpms, the sled probably hit about the same rpms but was a 2 stroke so im guessing i may have to modify it a bit. So has anyone done this before? any help is appreciated.

 

[Kaptain Krunch]

Also it was a twin cyl polaris indy, 440 i believe that it came off.

 

[jr dragster T]

A sled for 5 bucks? Thats so cheap you might as well not even give him any money lol. I guess its like when the car dealerships say "Only pay $0.01" just as a grab. The truth is that he was just giving the sled away and he made money off you lol.

 

[Kaptain Krunch]

A sled for 5 bucks? Thats so cheap you might as well not even give him any money lol. I guess its like when the car dealerships say "Only pay $0.01" just as a grab. The truth is that he was just giving the sled away and he made money off you lol.

The 5 was for gas money to my house. He said i could take it for free if i picked it up. Hes got another he'll deliver later for another 5 bucks, same kind of sled except its got a liquid 440 in it with one of the pistons melted into the cylinder.

So you have no info on the tach? im guessing one goes to the coil ones goes to ground? its got two black wires, a red, and a yellow coming off the back. I figure black is ground, but im not sure.

 

[ed1380]

does the guage illuminate?

 

[jr dragster T]

does the guage illuminate?

Hope it does, light up gauges are sick!

 

[Kaptain Krunch]

No it doesnt, i looked at the harness and the two black connect together, than the other two connect also so im gonna try grounding it and connecting it to the coil.

 

[EagleTalons]

I have a Volkswagen tach and I think it has four wires or some such thing on it and it illuminates.

 

[ed1380]

is the motor cdi ignition?

 

[Kaptain Krunch]

Not sure it had no engine, but im guessing it was. The engine im putting it on is cdi.

 

[Kaptain Krunch]

Good and bad news, i hooked it up to the ground and the plug and it just acted like a kill switch when i touched the wires, then i hooked it up to the headlight hookups and it showed 2k rpm idle and i know thats off by around 1200rpms, it was idling really low i could hear each fire and the cams moving and such, and when i gun it it went to 10k rpms and thats the top of the meter and i think it could have gone higher. So anyways it works but it doesnt read correctly, any ideas?

 

[ed1380]

each tach is programmed differently. some coils fire on the exhaust stroke too. meaning that the rpm is double

 

[jr dragster T]

Your 2 stroke has a cam shaft? Cool!

 

[Kaptain Krunch]

Your 2 stroke has a cam shaft? Cool!

Its a 4 stroke haha, so yea its reading double the rpms, is there anything i can do? resistors maybe?

Also i got the disc brakes off, the caliper is nice i need a new master cylinder but i'll just get one off a junk car, the disk is also in good condition and is exactly 1" bore with 1/4 key way!! totally worth the $5 haha, next sled is coming sunday, that one might be a little tricky, its a twin water cooled but one of the pistons is pretty much melted into the cylinder.

 

[Kenny_McCormic]

The 5 was for gas money to my house. He said i could take it for free if i picked it up. Hes got another he'll deliver later for another 5 bucks, same kind of sled except its got a liquid 440 in it with one of the pistons melted into the cylinder.

That can be repaired, jug might be saveable, depends on what its made from.

 

[Kaptain Krunch]

Yea, im hoping to either get both the cylinders bored or if thats a lot (no idea what it costs for a 2 cyl sled engine), i could try and run it on the one cylinder he told me was good, This is eventually going on a kart if i get it running, the sled is missing to many parts to get going again. The engine is just about complete, doesnt have fuel lines or primary clutch but i have a 3rd sled thats been sitting for 10 years because it has a hole in the piston, so i can get more parts from that.

 

[ed1380]

heres a circuit for you. put it in front of the tach. it has a rheostat on it to control the devision. im sure kibble wouldnt mind making one for you. he also has an o-scope that you need to calibrate it. just beware cause the cdi outputs around 250v
http://www.ecelab.com/circuit-frequency-divider.htm

 

[Kaptain Krunch]

heres a circuit for you. put it in front of the tach. it has a rheostat on it to control the devision. im sure kibble wouldnt mind making one for you. he also has an o-scope that you need to calibrate it. just beware cause the cdi outputs around 250v
http://www.ecelab.com/circuit-frequency-divider.htm

Looks fairly simple, i have the caps and i think i have some resistors and maybe some proto board, where could i get the IC? im a novice with electronics, i've only made a few things and the most complicated thing i made was a CMoy pocket amp, but i think i could do it. But i dont have an o-scope or the money to buy one, do i absolutely need it? Are you positive that will work? couldnt i just toss a rheostat in there without any fancy wiring to lower the voltage?

 

[ed1380]

the 555 is one of the most common ic's out there. radio shack should have them but they only work up to 15v. you need to be able to handle an imput of 250 and the tach might need an output of 250

 

[Kaptain Krunch]

the 555 is one of the most common ic's out there. radio shack should have them but they only work up to 15v. you need to be able to handle an imput of 250 and the tach might need an output of 250

250? maybe im wiring it to the wrong place, i have on wire going to the ground, and one going to a red output wire on the headlight that puts out about 10 or 12 volts (my multi meter is dead so i used a 12v car headlight and its pretty bright). I tried wiring one directly to the sparkplug wire and then the other to the ground but that just killed my spark.