Leccy rev counter

[cabbie]

Here's a question for leccy experts.

I bought an electronic rev counter off eBay, the guy said it works on 2 and 4 stroke engines, now, I'm a bit slow when it comes to wires etc but! the rev counter runs off a coil, so if a 2 stroke coil pulses every 2 rev and a 4 stroke coil pulses ever 4 revs how can the rev counter work on both engine and read the revs correctly?

Surely there must be two types, 1 with a 1:2 ratio and 1 with a 1:4 ratio.

[kaighn80]

no the 4 stroke coil fires every rev because its driving 2 spark plugs that are opposite ends of the 720 degree cycle and wastes the spark on the empty cylinder, on a 2 stroke i believe that they fire every 360 degrees because of the way they use reeds and piston position to serve as valves and valve timing.

[cagimaha]

You need to be careful here because you can get wasted spark two strokes and wasted spark four strokes. A wasted spark two stroke fires every 180 degrees of crank rotation. A standard two stroke and a wasted spark four stroke both fire every 360 degrees of crank rotation and a non wasted spark four stroke fires every 720. This all applies to a single cylinder setup. When you get into multiple cylinders, sharing coils and "V" engines it gets worse...

Some old school tachos on brit cars have a little switch on the back allowing you to select between several different settings. I imagine your purchase will be equipped with something similar. Hope this helps, Ben.

[cabbie]

Here's the item

http://cgi.ebay.co.uk/ELECTRONIC-TACHOMETE...otorcycle_Parts

The instructions just say "2 cylinder 4 stroke"

[cagimaha]

Hmmm that does look a little on the crude side. What motor are you planning on using it on? I have a sneaky suspicion it's set up for a wasted spark four stroke i.e. Z1000, GSXR1100, FZR1000 of 80's vintage.

[cabbie]

It's going on a kawasaki H2 750 triple 2 stroke

[kaighn80]

sorry i wasn't even aware of the wasted spark 2 stroke! you learn something new everyday ( i learn lots of new things every day but i think its the same stuff over and over but its just not sinking in!!)

[cagimaha]

See if this link helps. Basically because your motor is fairly unusual in that it's got a 120 degree crank I reckon you might struggle getting a "generic" tacho to work. Depends how it takes it's signal though. If it's just got a sensor wire which you wrap around one of the HT leads then I think it will probably work because as far as the tacho is concerned that one HT lead is acting as a wasted spark four stroke/non wasted spark two stroke.

I'm a bit crap at explaining but hopefully this link does a much better job:

http://www.scitsu.co.uk/docs/fitment.htm