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Is there a tool for measuring idle speed?

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Is there a tools for reading RPM at idle for a 2 stroke?  I don’t want one permanently mounted. Just wondering if there’s a way to get an accurate reading at idle for testing purposes. 

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There are many tachometers that are inductive and some expensive ones that pick up the signal like a radio. El Cheapo ones ($10) are just a wire wrapped around the coil or plug wire you do not have to mount the display. A Harbor Freight shop one is probably pretty cheap. Horribly expensive frequency counters work too.

https://www.ebay.com/itm/323436140802

https://www.harborfreight.com/lcd-automotive-multimeter-with-tachometer-kit-95670.html

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I wonder if there is an app for it? There seems to be apps for everything else. 

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3 minutes ago, Pipester said:

I wonder if there is an app for it? There seems to be apps for everything else. 

For an app to work, it would need an 'add-on' device to pick up the Rf generated by the ignition.

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2 minutes ago, William1 said:

For an app to work, it would need an 'add-on' device to pick up the Rf generated by the ignition.

Ahhh, gotcha. So much for smart phones. Pfffft can’t even measure idle speed lol.

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4 minutes ago, Pipester said:

Ahhh, gotcha. So much for smart phones. Pfffft can’t even measure idle speed lol.

You could if you were real clever. Calculate the primary, trans, secondary and wheel diameter to determine how fast the bike will move per rpm. Fire it up, idle in first gear. Using the phone GPS, get your speed. Then reverse the math to get the RPM. Be sure to take the sine of the angle of the ground, wind resistance and tire pressure in to the equation.

Back in the 1970's, my cafe racer had no speedo, just a tach. In third gear, the tach was close to speed, so 3,000 rpm was 30 mph.

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1 hour ago, William1 said:

There are many tachometers that are inductive and some expensive ones that pick up the signal like a radio. El Cheapo ones ($10) are just a wire wrapped around the coil or plug wire you do not have to mount the display. A Harbor Freight shop one is probably pretty cheap. Horribly expensive frequency counters work too.

https://www.ebay.com/itm/323436140802

https://www.harborfreight.com/lcd-automotive-multimeter-with-tachometer-kit-95670.html

My son raced karts for awhile and we used the same type of induction wire wrap tach, it had other bells and whistles too, but that's not important here.

Sometimes it helps to strip a few inches of the induction wire and coil it around several times. Much better readings than the ones with a little clip for the plug wire. I used heat shrink tube to hold the wire in place, but you'd be ok with electrical tape temporarily for tuning purposes. 

Cheers

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2 hours ago, William1 said:

There are many tachometers that are inductive and some expensive ones that pick up the signal like a radio. El Cheapo ones ($10) are just a wire wrapped around the coil or plug wire you do not have to mount the display.

https://www.ebay.com/itm/323436140802

 

I have mounted inexpensive Tach/Hour meters like these on all of my 2-stroke and 4-stroke dirt bikes.  I mount them so that I can see them while sitting on the bike.  They are very useful not only for idle speeds but for rpm levels when running at constant speeds.  

Edited by Chas_M
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Another vote for the Treysit Sirometer. Everybody should play with one just for the cool factor. I love simple engineering like this. Clay

E795BEED-AC48-4526-AE54-1C604DF0FC2D.jpeg

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11 hours ago, Pipester said:

Ahhh, gotcha. So much for smart phones. Pfffft can’t even measure idle speed lol.

There are apps that apparently use your phone's proximity sensor but I haven't tried and not sure how accurate they would be but I'd be interested to hear :)

Android - https://www.google.ca/search?ei=-MfHW8uNBKaE0wLk3KaQDQ&q=tachometer+app+for+android&oq=tachometer+app&gs_l=psy-ab.1.1.0l4j0i22i30k1l4j0i22i10i30k1j0i22i30k1.1319.2509.0.5129.4.4.0.0.0.0.465.691.0j2j4-1.3.0....0...1c.1.64.psy-ab..1.3.686...0i67k1.0.NJ4rqgU0m6c

Just found this Digital Laser Non-Contact Photo Tachometer RPM Measurer with LED Laser

https://www.instrumentchoice.com.au/instrument-choice/other-meters/dm-6234p-digital-laser-non-contact-photo-tachometer-rpm-measurer-with-led-laser-for-hvac-automotive-

IC-TAC-01.png?Action=thumbnail&Width=512

Otherwise a variety of types here for an example

https://www.amazon.ca/Briggs-Stratton-19200-Tachometer/dp/B0044AV5VK

 

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11 hours ago, William1 said:

You could if you were real clever. Calculate the primary, trans, secondary and wheel diameter to determine how fast the bike will move per rpm. Fire it up, idle in first gear. Using the phone GPS, get your speed. Then reverse the math to get the RPM. Be sure to take the sine of the angle of the ground, wind resistance and tire pressure in to the equation.

Back in the 1970's, my cafe racer had no speedo, just a tach. In third gear, the tach was close to speed, so 3,000 rpm was 30 mph.

Ddddddeeeeerrrppppp????

good thing I’m not that clever. 

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30 minutes ago, filterx said:

Those only work if you can see the flywheel or cam. You need to put a stripe on the flywheel and they 'see' the mark as it passes. On a dirt bike, you could use it on some 2S that do not have an oil bath on the flywheel. Paint the flywheel black and put a stripe on it.

I use that kind of a tack for setting lawn mower engines, chain saws, weed wackers. Not practical on a bike or most automotive engines.

5 hours ago, RichBaker said:

Treysit Sirometer.....  It's what we use in tech when we sound check your loud ass bikes.

 

https://www.ehow.com/how_8745998_use-treysit-sirometer.html

Ah, I forgot about the vibrating reeds!

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Simpliest is an hour/tach.  Ive run them inside a radiator shroud. Invisible and weighs nothing. Why not permanent?

 Im curious. Testing what?

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The cheap kind on amazon that wraps around the spark plug wire. However, they are not all the same. I can't remember if it says "updated" or what. But some only measure in 200 rpm increments and that is worthless. The last 2 I bought measured in 20 rpm increments. On a 4T it will read steady. On a 2T it tends to be a little less steady, but actually more valuable because a "gallop" on a 2T is not indication of better running

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tried some apps, it just counts the firing sound. Should work on a single cyl but I never got it working. The app should work, but is limited more by the phone's processing of the sound. And +1 on making sure your tach has allow enough resolution, othrwise worthless for idle speed.

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If you get an app that do sound frequency analysis, such as Spectiod on Android, you can easily get the frequency of the power pop. Multiply by 60 and you have RPM.

The wrap on the spark plug wire hour meter/tachs work too, but Spectoid is free if you have a smartphone.

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Electronic Specialties 328 EZ Tach Plus

Picks up signal wireless or with supplied inductive pickup

I just ordered one yesterday, so I can not say how well it works. Reviews said the wireless signal was "iffy", but I plan on clipping the pickup to the spark plug wire

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15 hours ago, RawbW said:

Ear and feel!

And some guys use their tongue for testing 9v batteries.

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