Topic: Accurate Tach With 50 RPM Graduations

[DaveBarbier]

The book says to adjust the pilot screws with a tach that has graduations of 50 rpm or smaller and that can accurately indicate a 50rpm change. What kind of tach would they be referring to? Would shops that used this method be using one of those analog tach/dwell/points resistance meters?

Does anyone here actually use this method?

[scottly]

Does anyone here actually use this method?

Not me.

[Deltarider]

Which book is that?

[DaveBarbier]

Which book is that?

650 FSM

[Alan F.]

Over the summer I picked up a Tach/Dwell/Voltmeter just like this photo but a few decades older, I tested DC volts only and it was spot on to my (employer supplied) Fluke meter.





This reads in 50 RPM increments and I'll give it a try when I've got a bike together. They're still available online if you check around.

[DaveBarbier]

Over the summer I picked up a Tach/Dwell/Voltmeter just like this photo but a few decades older, I tested DC volts only and it was spot on to my (employer supplied) Fluke meter.





This reads in 50 RPM increments and I'll give it a try when I've got a bike together. They're still available online if you check around.

Ahh, I see. Very different that what I was expecting. I was looking all around for cable driven tachometers. But this seems to connect to the points or coil or something. Technically this one you posted measures the rpm in 100 rpm increments because it says to double the 8 cylinder scale for 4 cyl but I’m being a little pedantic. I bet it would work totally fine. I’ll have a look out for these old school tach, volt, dwell meters, thanks!

[robvangulik]

I looked this device up on google and most comments are negative concerning dwell and rpm measurements....

[DaveBarbier]

I looked this device up on google and most comments are negative concerning dwell and rpm measurements....

This Actron model or these kinds of devices in general? I found a Snap On on Craigslist fairly close to me for a song, awaiting the seller’s reply.

[seanbarney41]

I have owned a few Actron gauges over the years...they are cheap and easily damaged.  They work ok until you drop or bump them or whatever...not really the best ticket for garage and/or workshop use.

[Alan F.]

The version I bought is SEARS, the other was just for illustrative purposes but thanks for looking up reliability.







Looks easy enough to repair if anything goes wrong. I was taught to never drop electronic equipment although I confess to having it happen at times.

Owners manual download: https://www.google.com/url?sa=t&source=web&rct=j&url=https://c.searspartsdirect.com/mmh/pd_download/lis_pdf/OWNM/1006230L.pdf&ved=2ahUKEwic0IWO6oDuAhW7GVkFHcuVDcsQFjAJegQIBRAB&usg=AOvVaw2C6zQuEy9WKrV32sVJRc1h&cshid=1609713607811

How to use on your SOHC4:
http://forums.sohc4.net/index.php?topic=25952.0

[DaveBarbier]

The version I bought is SEARS, the other was just for illustrative purposes but thanks for looking up reliability.







Looks easy enough to repair if anything goes wrong. I was taught to never drop electronic equipment although I confess to having it happen at times.

Owners manual download: https://www.google.com/url?sa=t&source=web&rct=j&url=https://c.searspartsdirect.com/mmh/pd_download/lis_pdf/OWNM/1006230L.pdf&ved=2ahUKEwic0IWO6oDuAhW7GVkFHcuVDcsQFjAJegQIBRAB&usg=AOvVaw2C6zQuEy9WKrV32sVJRc1h&cshid=1609713607811

How to use on your SOHC4:
http://forums.sohc4.net/index.php?topic=25952.0

Cool, thanks for the post 

[DaveBarbier]

Over the summer I picked up a Tach/Dwell/Voltmeter just like this photo but a few decades older, I tested DC volts only and it was spot on to my (employer supplied) Fluke meter.





This reads in 50 RPM increments and I'll give it a try when I've got a bike together. They're still available online if you check around.

Alan, I posted before that it says you’d have to double the 8 cyl readings for 4 cyl but since our engines are wasted spark I may be wrong. You might be able to read the 8 cyl scale directly. I’d be very interested to know if this is the case. Once you get your bike together give it a test. Unless you have another vehicle you can test on. Hopefully I’ll be picking one of these up soon so I can do my own tests. I have a digital tach that’s accurate but just watching a blur of numbers doesn’t help me. Like looking at a digital clock vs an analog. Nothing like a sweeping needle.

[drumstyx]

FSM probably refers to an old fashioned gauge like the ones above, but digital tachs are available now, with both inductive pickups and coil lead inputs...they can read, theoretically, down to 1rpm.

That said, unless you're LOOKING for small variations (adjusting pilot screws individually) and can't hear/feel them, you don't really need that accuracy.

[DaveBarbier]

FSM probably refers to an old fashioned gauge like the ones above, but digital tachs are available now, with both inductive pickups and coil lead inputs...they can read, theoretically, down to 1rpm.

That said, unless you're LOOKING for small variations (adjusting pilot screws individually) and can't hear/feel them, you don't really need that accuracy.

That’s exactly what the book is trying to help you perform, pilot screw adjustments. And I think the problem with the digital tachs is that they’re so accurate all you see is a blur of numbers. Like I posted above, a sweeping needle is so much easier to grasp. The digital tachometer is one of the worst inventions ever.

[Erny]

FSM probably refers to an old fashioned gauge like the ones above, but digital tachs are available now, with both inductive pickups and coil lead inputs...they can read, theoretically, down to 1rpm.

That said, unless you're LOOKING for small variations (adjusting pilot screws individually) and can't hear/feel them, you don't really need that accuracy.

1 RPM resolution on digital tach is pure theory. The problem of digital tachs is that in low (idle) RPMs there are too low qty of "impulses" coming from pickup that A/D convertor makes reading jumping +/- 10 RPMs on most of tachs I have seen.And this is not really usable for required purpose.
Analogue tach as one listed here is in advantage as you can see even small movement of gauge - and this is what you need, to see how movement of idle screw is changing RPM (you don't really care about absolute value itself, important is to see if it increases or decreases)

[Bodi]

I've just used the bike's tach, unless it has a problem with staying steady (ie a jumpy cable) - I can see the RPM change as the mixture screws are adjusted. Absolute RPM isn't so important. Idle RPM should be around 1100 RPM with a warm/hot engine but it is not at all critical.

[Deltarider]

... I think the problem with the digital tachs is that they’re so accurate all you see is a blur of numbers. Like I posted above, a sweeping needle is so much easier to grasp. The digital tachometer is one of the worst inventions ever.

Actually there are a lot of measurements that are much easier to read analogue: Volts, Dwell, RPM, % CO to mention a few. That Actron looks like a suitable meter. Usually even the cheap ones are accurate. If equipped with a d'Arsonval meter, so much the better. Meters for the DIY market are cheap because of the inferior quality cables and plastic casing that is far from rugged.
I do not know much about electronics, but I wonder If you could create a 'true' RPM reading without having to multiply what you see displayed by 2 and so have finer increments. Could it be done by connecting the pulse probe via a splice to both points with a diode fitted in each (sub)lead? I suppose it could work with a duty dycle less than 50%, but probably not with the 51,1-54,4% prescribed for our ignitions. Any of you have a suggestion?
From experience I cannot recommend the RPM method for the CB500/550. These models need a relative rich idle to compensate the lack of acceleration jets and so facilitate an acceptable driveability. I've tried and found it very, very time consuming. I'd rather use a CO meter.

[DaveBarbier]

Yeah, since the 650 has an accelerator pump it likes a leaner idle mixture. How much leaner? Not sure, but I want to set the pilot screws by the book and see how it goes.

[DaveBarbier]

A buddy of mine found one in his old man’s garage. 20rpm increments. Perfect. Going to test it out now. Hope it doesn’t catch fire.

[DaveBarbier]

Hmm, bike won’t start with it connected and it stalls the bike out if I connect it while it’s running. Possible I have it connected wrong but also it might put too much of a load on the ignition circuit. I’ll try and find the manual online. Don’t want to fry anything.

[DaveBarbier]

No one here would happen to know how this gets hooked up, would they?

The green and black on the left gets me to measure voltage from the battery. Black negative, green positive. There is no manual on the internet for this.

[Deltarider]

There is not much you can do wrong when 'Volts' is selected.
Just don't switch it to 'Amps'. In this mode a mistake is easily made. On these oldstyle devices the ammeter usually is very inaccurate anyway, so I wouldn't bother to use it.
And when 'Ohms' is selected, make sure there's no current in what ever you measure. But... you probably won't need this either; any cheap DMM does it better.
To measure either 'Dwell' or 'Tach' one probe goes to the little bolt of the breakerpoints (or the coils minus for that matter) and the other to chassis.
The one that I am not familiar with is the 'kV' scale (switch position in 'Ignition'). Could it be that the big red clamp is to be clamped around a high tension plug wire?

[DaveBarbier]

To measure either 'Dwell' or 'Tach' one probe goes to the little bolt of the breakerpoints (or the coils minus for that matter) and the other to chassis.

That’s the thing, I’m trying to figure out which leads. The tach function is what I’m trying to use. I have tried so many different combinations. It very well could be that the tach part of the meter is busted. Volts works though.

My friend’s father wrote this down but it’s incorrect.

[jonda500]

I think Delta was on the right track, - I think the large red clamp goes on battery positive, the little red one goes on coil negative(the points wire), and the little black one goes to ground(battery negative). I don't know what the other two are for...
John

[DaveBarbier]

I know that something goes to the signal wire to the coil and another to ground and tried that and it wouldn’t let the bike start (struggle to fire) and it would stall the bike if I attached them while running. But I did not try and clip the big red one to the battery positive. I’ll try that tomorrow, thanks for the suggestion.