Workshop tachometer.

[royhall]

Looking for an automotive multimeter with induction loop, mainly for the RPM setting to set up the slow idle screws (but also for other functions). Has anybody got any recommendations, must be affordable as it wont be used much. Also am I correct in saying that for ignition purposes a CB750 is twin cylinder due to the lost spark thingy. Most multimeters seem to do 4,6 &  cylinders? Cheers.

[Bitsa (Ralph Wright - RIP)]

Royall
Its not a lost spark but a wasted spark 1-4 spark together same as 2-3
Cheers
Bitsa

[matthewmosse]

I have a laser tachometer, reads a white stripe of paint or tipex with a laser just like a barcode scanner and tels you the rpm, it was under £15 off ebay but seems to do the job ok - not bought for bike, I used it to setup our landrover  and haybaler to roughly the right rpm, but it comes in handy for testing what rpm mystery electric motors off ebay run at etc.
If you prefer the multi meter option go to a few classic vehicle rallies with auto jumbles. I don't do electronics if I can at all help it but have a collection of multi metres etc from auto jumbles to test and see what I get on with, I've picked up Gunson's and Avo metres for under £5 each in the past few years. Can be worth going to those events just for the cheap auto jumbles. 

[royhall]

Cheers Bitsa. Couldn't just remember what they called that spark (due to the lost spark thingy) just when I was writing it. Senior moment again. Am I correct in saying for ignition purposes its effectively a twin cylinder. Can matter on some multimeters with RPM function. Electrics isnt my strong point but am learning rapidly, shame I will have forgotten it all by the time I do the next bike. Ohh to be 21 again.

[Bitsa (Ralph Wright - RIP)]

No worries have em all the time.You have a multimeter with rev counter on it?Never seen one my strobe light does have a counter on it though.
Cheers
Bitsa

[Lobo]

Hi Roy,

As far as I understand it the induction loop clips around a (any) spark plug HT lead. The meter then counts the HT pulses (ie sparks); works out the equivalent number over a minute; & then displays this as number of sparks / minute.... Ie RPM. There is only one meter selection to make... ie 2 stroke or 4 stroke.

If its a 2 stroke the pulses will be one / revolution, and the read out directly according to a minutes worth. 

If its a 4-stroke the pulses will be every other revolution, ie the digital readout value will be double the value of the sensed pulses / min to indicate the correct RPM.

You have a good old SOHC with its wasted spark, ie firing every revolution. As far as the meter's concerned its a 2-stroke (sacre-bleu!) .... and so you should select this on the setting.

The multiple cylinder selections are for dwell angle values, when the thing is typically connected to the distributer.

As a parting comment, can I suggest you use your ears & nous .... ie if the tick-over sounds like 1200.... but the meter says 600... well just double all values you see.

Honestly I've never owned such a meter, and stand to be fully corrected.

Often you can download PDF instructions to these meters.... might be worth a look if you've a certain one in mind.

Simon

PS.... just found these below off such a PDF file...

[royhall]

Cheers Simon your a handy chap to have on here. Have decided on a meter on EBay, http://www.eBay.co.uk/itm/261135696592?_trksid=p2060778.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT. Think it will do everything I need, and not too dear at £55. Now I think about it your right about the two stroke thing, I knew it should be divided by two for some reason just couldn't remember why. Two stroke not twin cylinder. Jeez I think I may be getting thicker. Cheers for your help.
PS. Not managed to fix the indicators on my other bike yet, turning into a real mystery? May have to enlist professional help on that one.

[Lobo]

That meter looks the bees knees... good to see it has a 10A capability.

Am 'disappointed' you didn't get to the bottom of your indicator issue... have posted there.

Cheers,
Simon