How do you tune without a tacho

Pork Chop

XS400 Junkie
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I plan on running a speedo only and wondered how you speedo-only guys tune your bikes.
Do you use an electronic tacho like this one?

Also, when I remove the cam cover I actually ripped out the tacho cable because the locking screw was stripped so unless I get a new cable I wont be able to use the old one as a temp tuning aid.

Cheers,

Pork Chop
 
Posted this for Fubar a while ago:
If you want to use math, you can take your 1250 RPM and use gear ratios to find out how fast your bike would be going at idle with the clutch out. When you want to set it, lift your back tire and let the bike coast at idle with the clutch out in 1st gear. Let me show you what I mean:
1250 RPM at idle
x 2.5:1 in first gear (you can pick a different gear and find the ratios from the manual to get a higher speedo reading)
x 37:17 rear:front sprocket (not sure what the actual ratio is)
x 6.28*radius of wheel + tire (be exact)
so that will give you your speed in inches/min, convert it to kph or mph and youll have your speedo reading to tune your idle with
 
If you are just asking about idle speed, you can set that by ear. Not too high, not too low and you will be fine. No real magic to it and the factory recommended 1200 rpm is really only a reference point.
 
I think you have a calculation reversed somewhere (remember that the driving wheel spins slower in a lower gear). When I crunched the numbers I got a value that was absolutely way off in the opposite direction (it should be something like 5-10 kph) so I'm obviously missing a ratio or variable somewhere.
From what I've dug up on the forum, in top gear you should be hitting 100kph at about 6000 RPM. Using that same logic, at 1250 RPM you ought to hit something near 20kph in top gear.
 
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