Topic: Solved: How to Test Actual RPM

[Kaze]

EDIT: I need a tachometer to do maintenance, not for riding. I didn't know that Honda didn't expect bike's tachometer to be accurate enough for testing and maintenance. My tachometer reads 1400rpm, but sounds more like 900-1000rpm and cannot go lower without dying. So I thought my tachometer was broken.

QUESTION: What are different ways that I can test the actual RPM?

ANSWER: Many dwell meters have a tachometer function, whether analog or digital.
The old "Sears" analog dwell/tach/voltmeter can be found on Ebay for $50-$100. (Many sellers don't test them.)

[PeWe]

Wrong tachometer?
I bought a late CB500 tacho by mistake. Same color and size as my K6 speedo.
Red line started later.

It showed much different revs when I finally started the bike, first renovation after the long sleep late 1990-2013

[jgger]

When you buy that dwell meter you mentioned in the other thread, get one that also has a tach function. EZPZ

[Deltarider]

When you buy that dwell meter you mentioned in the other thread, get one that also has a tach function. EZPZ

They all do. Consider an analogue one. They are cheap secondhand and a joy to work with.

[Kaze]

I've seen several people mention the old SEARS Tach/Dwell/Voltmeter. $80 on Ebay. If they are analog, I suppose the odds are in my favor that it will still work (in spite of being used). Anybody think this is a terrible idea?

[PeWe]

You do not have access to  another CB750 tacho to test with?

Old but working K3-K6 are rather common.
The idle can be that bad and stumbling so it runs very uneven at that relatively high idle.

[dave500]

any decent digital multimeter with dwell/tach is the go,how #$%*ing hard is it?dont worry about the actual number of the idle rpm,so long as it sounds right and idles smooth who gives a #$%*?if your riding an old honda four you aint gonna be idling anyhow but for a few minutes!

[Deltarider]

I mentioned the analogue ones because I prefer working with them when test is done dynamically and then only for dwell, tach and volts. For all other measurements I use my digital one. The latter always travels with me. Both analogue ones I have, are too bulky. Also realise that analogue meters of that era suck for measuring amps and resistances. Digital do that much better. So maybe you are better of with a digital one after all. Just select the 8 cyl position to arrive at an acceptable reading and less everchanging digits. Both my analogue ones I got for $ 10,- secondhand. That's why I gave the suggestion.

[dave500]

Deltas bike still has the japanese factory workers finger prints on it.

[Deltarider]

Deltas bike still has the japanese factory workers finger prints on it.

In Honda factories, all workers were in spotless white overalls and wore thin white gloves. There wasn't a drop of oil on the floor. https://www.youtube.com/watch?app=desktop&v=ELNJisDN_ss

[Kelly E]

Don't forget i have a set of 750 gauges you can have. I also have a timing light with a tach and dwell you can borrow.

[Kaze]

..dont worry about the actual number of the idle rpm

But Dave? I have to know where the actual red-line ends, so I can safely get through red back to where it turns green again! My redline ends at 9,300rpm so... 10k is where the gravy is. HAHAHA

[Stev-o]

dont worry about the actual number of the idle rpm,so long as it sounds right and idles smooth...

Dave never sugar coats his posts but this one is really spot on.  These old gauges are not accurate, at least 10% off. 

[Kaze]

Dave talks the way I understand. If I want sugar, I'll grab a cookie.

[Kaze]

Just a final comment from me here, I had no idea that Honda didn't expect bike's tachometer to be accurate enough for testing and maintenance*. My tachometer reads 1400rpm, but sounds more like 900-1000rpm and cannot go lower without dying, so I thought my tachometer was broken. I need a tachometer to do maintenance, not for riding. So now I know I need to buy a tach/dwell/voltage meter. Thanks guys.

* SeanBarney41 pointed out that this mentioned in the manual. I just never got to that page.

[Bankerdanny]

EDIT: I need a tachometer to do maintenance, not for riding. I didn't know that Honda didn't expect bike's tachometer to be accurate enough for testing and maintenance. My tachometer reads 1400rpm, but sounds more like 900-1000rpm and cannot go lower without dying. So I thought my tachometer was broken.

QUESTION: What are different ways that I can test the actual RPM?

ANSWER: Many dwell meters have a tachometer function, whether analog or digital.
The old "Sears" analog dwell/tach/voltmeter can be found on Ebay for $50-$100. (Many sellers don't test them.)

I was just going to reply this. I have one of those old Sears analog meters that belonged to my dad. It's one of my prized possessions.

[Kaze]

Dad tools are great. Dad's been gone a long time but his tools and curse words remain.

I went over to Kelly's shop, and we hooked up his tach meter. My tach is pretty close to accurate. Only off by about... 100-200rpm. So it just doesn't want to idle at 1000rpm or it dies. Onto the next issue I guess.

[bryanj]

Never did get a four to consistently idle at 1000 even new, always set them at 1100 to 1150

[Stev-o]

... but his tools and curse words remain.

Kaze - I saw that your sig once said that he told you not to be a "candy ass".  My Dad also used that phrase and it made me smile, miss hearing his stories.

[MauiK3]

I have my grandfathers 0-1" micrometer, I'm sure it's over 100 years old. Works perfectly, I use it all the time. It measures to 0.0001"

[flybackwards]

My timing light has a tach display on it - just have to remember to divide by two on the Hondas

[Don R]

... but his tools and curse words remain.

Kaze - I saw that your sig once said that he told you not to be a "candy ass".  My Dad also used that phrase and it made me smile, miss hearing his stories.

 A late co-worker used to say, we need to soak your socks in kerosene, so the ants don't eat your candy ass!

[Kaze]

A late co-worker used to say, we need to soak your socks in kerosene, so the ants don't eat your candy ass!

Hahahahaha!

I got all kinds of variations of candy-ass comments from dad. He was a WWII vet / Depression era dad, 20 year retired service man. My classmates' parents were either ex-hippies or at least of that generation. Not my folks. On the weekend Dad would grab the matress at 8am and lift up the corner and ask "You gonna sleep all day!?"

He literally came in one morning and said "drop your cock and grab your socks". Mom let him have it for that one, but I figured he'd been in a war, and probably killed people, so I wasn't about to argue.

BryanJ: that comment is VERY useful. Thanks for that.

[Stev-o]

A late co-worker used to say, we need to soak your socks in kerosene, so the ants don't eat your candy ass!

I got all kinds of variations of candy-ass comments from dad. He was a WWII vet ...

My Dad was also a WWII vet - the Italian army!  [No BS]  He also said every guy should spend at least one year in the service, I did not agree and didnt serve.

[Deltarider]

A late co-worker used to say, we need to soak your socks in kerosene, so the ants don't eat your candy ass!

I got all kinds of variations of candy-ass comments from dad. He was a WWII vet ...

My Dad was also a WWII vet - the Italian army!  [No BS]  He also said every guy should spend at least one year in the service, I did not agree and didnt serve.

What?! Not even in the boy scouts?