testing RPM

[Viktory2k1]

ok read the manual for my meter: "touch black probe to a good ground, touch red probe to the negitive side of of coil primary winding." What is negitive side of coil primary winding? the coils just have a positve from cdi. dont want to ruin meter. I will use the alligator clips for this. See wiring updates topic for pics of meter.

[harleysportster]

Vic,
You have a nice meter but I don't think it is correct for testing the rpm's of your Cyclone.
There is a difference between an automotive ignition system and the snowmobiles. The automotive type is powered by DC current(direct current ) from the battey. The voltage to the coil is anywhere from 6 volts to 12 volts depending on the manufacture. The older cars with points usually had a resistor that cut the voltage down to around 6-9 volts.
The ignition system on the JD snowmobiles is AC (alternating current) The lights are actually supplied with AC current too from the stator.
The stator has two divisions of windings, one for the lighting and one for the ignition but both are AC voltage. To confuse you even more, the tach is recieving an impulse AC signal from the lighting circuit of the stator.
Given that info, an automotive type tachometer cannot be used to test the jd engines. You can replace your Cyclone tach with any tach that is used on a prestolite cdi system from a '75 295/s, '75 340/s, '75 800, '76 Liquidator, '76 400, 76 -78 Cyclone / Liquifire. The Liquidator/Cyclone / Liquifire tachs maxed out at 10,000 rpm but the other type of 8,000 will work too.

[JDGuy]

Amazon had these for about $50. Electronic Specialties, Inc. http://www.esitest.com Model 328 EZ Tach. Worked good for me on lawn tractor and a couple of other small engines, but I never used it on a sled. Has mode settings for engine type, cycles, cylinders, etc. Clip lead on plug wire. Specs say 0-20,000 RPM 10 RPM accuracy.

[harleysportster]

Guy, thanks for sharing. That looks like it will do the trick.
http://www.youtube.com/watch?v=O6t8eVBlqBM&safe=active

[Viktory2k1]

There are 4 ways to test RPM with this meter: The way I desribed before, use the capacitive pickup on secondary, use the inductive pickup on secondary, or use the Phototach accessory(which I do not have). I will try the inductive pickup. I do have to set #of cyls and 2 or 4 stroke but will post results. Looks like this meter has that other one built in. Also more belt/clutch discoveries. Be back soon.....

[Viktory2k1]

Ok, I tested it and to some bad pics but meter seemed to read half of what tach said. I thought I set it right. I also checked clutch distance using just a tape measure. While holding tape to centerline of bolts, it was just shy of 11.5" but in pic with tape laying on bumper, it looks much closer. I think pic turned out bad and doesn't show a good reading. According to tach, engine idled at 2500RPM and clutch engaged at just under 4000RPM but then idled down to 3000RPM but motor returned to exactly where it was before. I thing 4500-4750 would be a better engagement RPM. Forgot to look to see what hole spring is in on driven. Pics following....

[nick80lf]

Setting up inductive Tachs always seems to get a little weird for me, I always have to stop and think about it. I'm positive that the 80 Liquifires fire a spark at the same time on both plugs. This means that a plug fires twice per revolution. I'm not really familiar with your sled, but I thought that they were different and only sparked once per revolution. This could account for the 1/2 reading.

[400brian]

I believe it is correct that the Prestolite does NOT use waste spark, it fires once per revolution.

[lwb140]

I believe it is correct that the Prestolite does NOT use waste spark, it fires once per revolution.

brian i agree this came about for me with the rebuilt cdi a few years back with the coil wires on it having reverse colors , there has been much discussion aboutthat since , if that werent the case it wouldnt matter which wire was which wade