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Discussion Starter #1
My Buddy Bucknutz found us each small little digital tachometer/hour meters. The tach reads pulse off the spark plug wire. It can be set to read in three different modes. #1 is it reads the spark plug fire twice per engine revolution. #2 it reads the plug fire once per revolution and #3 it reads the plug fire every other revolution. I'm not sure what the setting should be for the 4 stroke TW.

I also don't recall off hand what the basic idle RPMs should be but I seem to remember it should be right around 1100. I could set the tach read mode by that if I was sure.

Any help out here?

Thanks

GaryL
 

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If I recall, Idle speed is ~ 1,300 rpm.

Verified from manual... 1350 to 1450 rpm.

jb
 

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Discussion Starter #3
If I recall, Idle speed is ~ 1,300 rpm.

Verified from manual... 1350 to 1450 rpm.

jb
Thanks JB. So this tells me that #2 is the right setting, plug fires one time per revolution and my idle is set right at 1340.

GaryL
 

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It is my understanding (please correct me if this is wrong) that the TW has a wasted spark ignition, meaning that the spark plug fires on each revolution (i.e., both on the compression stroke and the exhaust stroke). Therefore mode #2 should be used. Idle speed should be somewhere around 1,000 rpm, depending upon your personal preference, and your bike's state of tune.

I had one of these (Tiny Tach brand) on my XR650L and found it to be useful. There was, however, a noticeable delay in the readout and it incremented by 50 rpms (i.e., 950, 1,000, 1050, etc.)
 

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I think our TW's fire twice with a wasted spark ignition. Once on the compression stroke, once on the exhaust stroke.
 

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Discussion Starter #6
It is my understanding (please correct me if this is wrong) that the TW has a wasted spark ignition, meaning that the spark plug fires on each revolution (i.e., both on the compression stroke and the exhaust stroke). Therefore mode #2 should be used. Idle speed should be somewhere around 1,000 rpm, depending upon your personal preference, and your bike's state of tune.

I had one of these (Tiny Tach brand) on my XR650L and found it to be useful. There was, however, a noticeable delay in the readout and it incremented by 50 rpms (i.e., 950, 1,000, 1050, etc.)
This one registers in increments of tens, 1340, 1350, 1360. I am actually more interested in the hour meter just so I have a good idea of how many engine hours have been logged.GaryL
 

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Gary, where did you get these? I might be interested in getting one.
 

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Discussion Starter #8
I think our TW's fire twice with a wasted spark ignition. Once on the compression stroke, once on the exhaust stroke.
This gets us into the discussion of What is 4 Stroke. I think it simply means that for every full revolution of the crank there are four separate strokes, Intake, compression, combustion and exhaust.

If in fact the plug fires twice with every revolution then my bike is idling at around 620 RPMs and that can't be right.

GaryL
 

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Discussion Starter #9
Gary, where did you get these? I might be interested in getting one.
Dave, Bucknutz, found them maybe on Ebay for around $12-15 each and grabbed one for each of us. I will check with him and post the info here when he responds.

GaryL
 

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Discussion Starter #11
A 4 stroke (suck, squeeze, bang, blow) requires 2 complete revolutions.
That explains the "Wasted plug firing" and why setting number 2 is right, plug fires one time for every revolution.

GaryL
 

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Discussion Starter #13 (Edited)
Gary,

I got this one and the settings and rpm icrements sound the same as you describe. I picked #2 for RPM's and it was right (1,100-1,500 ish).
That is the exact same one that we have and it works fine and was simple to install. What is really funny is I also have that same temp gauge but have not installed it on the bike yet! Actually I am looking for one that flips between Temp and Time.

GaryL
 

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What TW-Brian said ^^^

One successful firing sequence every two revolutions - although it may spark every revolution - that's why two-stokes are faster ......

A "stroke" is not a "revolution"
 

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Here is a 4 cycle engine animation I found on Youtube. Intake on the right, exhaust on the left. Also shows what over revving can do, watch the ending.

[/video]
 

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Discussion Starter #16
Go back up to what TW Brian said about the wasted plug firing on every full revolution of the crank. I have it set in number 2 which is the plug fires on every full revolution. I would have thought that setting number 3 should be used which is for the plug firing on every other full revolution as this graphic shows for the 4 stroke motor. The tach lead wire is wrapped around the spark plug coil wire and it only reads a signal when the plug fires. Apparently our TW engines fire the plug on every full revolution of the crank. It is pretty nice to know the RPMs and setting #2 is reporting the correct info.

GaryL
 

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Every revolution of the crank counts as “RPM” – however, not every revolution is a “power stroke” - except on two-strokes.

Setting No 2 should do for the TW - many bikes fire at every revolution

Almost every bike I’ve had chuckled over quietly at 1200 rpm – 1350 to 1450 seems a little “high” ……
 
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