Chuck
Useful idiot
I have a 1980 XS650 Special. The tachometer reads too high of an RPM. At lower rpm, 2000-2500 RPM, its about 200 RPM too fast. At higher RPM, 4250, it reads about 500 RPM too fast. Does anyone else have the same problem?
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Tachometer reads too fast
- Thread starter Chuck
- Start date
angus67
Welder's penetrate deeper!!
what tach do you have? stock? aftermarket?
If you have the stock tack, it is unlikely that its wrong, becuase it is gear driven, either it works right, or its broke, and shows nothing.
If you have the stock tack, it is unlikely that its wrong, becuase it is gear driven, either it works right, or its broke, and shows nothing.
jchrisk1
XS650 Junkie
My aftermarket tach did that. Then broke two weeks later. POS.
Chuck
Useful idiot
It’s a stock tachometer. My method is to use the well-known spreadsheet for Gear Ratios/RPM/Speed xs650revs.xls by pamcopete and compare what my speedometer indicated speed is to my RPMs. I test how well my speedometer works using the radar sped signs they have all over my town, they flash how fast I am going and I just look down and see if its right. My speedometer is 1-2 miles per hour slow. However RPMs are way off my indicated speed (with a little mental fix for the error noted). Based on this, I know the RPMs indicated are way too fast.
My understanding is that it is gear driven up to a point. At the tach it uses a magnet that pushes the gauge to indicate the RPM. So I figure, yes the gauge can be off even if mechanical. Really, I just wanted to know if this is a known issue. Of if I am full of shit. A possibility.
Spreadsheet example: correcting the spreadsheet for the size of rear wheel for special 16" wheel and using 17-34 gears, 5th gear is supposed to be 4280 RPM at 60mph. Mine reads 4750-4800. I suppose you could ask how do you know you are going 60? Can't absolutely confirm but the speedometer is mostly correct from other tests. Plus I am not blowing by people on the freeway; I am in the slow lane getting passed actually.
Would it be easier to have my wife drive alongside me on the freeway giving me speeds etc? Yes you would think so, if you were not married. Wait this last sentence belongs to another thread…
My understanding is that it is gear driven up to a point. At the tach it uses a magnet that pushes the gauge to indicate the RPM. So I figure, yes the gauge can be off even if mechanical. Really, I just wanted to know if this is a known issue. Of if I am full of shit. A possibility.
Spreadsheet example: correcting the spreadsheet for the size of rear wheel for special 16" wheel and using 17-34 gears, 5th gear is supposed to be 4280 RPM at 60mph. Mine reads 4750-4800. I suppose you could ask how do you know you are going 60? Can't absolutely confirm but the speedometer is mostly correct from other tests. Plus I am not blowing by people on the freeway; I am in the slow lane getting passed actually.
Would it be easier to have my wife drive alongside me on the freeway giving me speeds etc? Yes you would think so, if you were not married. Wait this last sentence belongs to another thread…
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The Speedo and tach will read slow when there is damage to the magnet drive inside or if it has been sitting, they somtimes free up with use.
What is the history of the gauge. Did this happen overnight, is this a new aquisition, has the po taken the gauge apart. You will see damage to the bezel if the gauge has been dismantled
Need to know the answers to be able to help you more
What is the history of the gauge. Did this happen overnight, is this a new aquisition, has the po taken the gauge apart. You will see damage to the bezel if the gauge has been dismantled
Need to know the answers to be able to help you more
bowhoc95
bowhoc95
Chuck, I run 16" rear 17-34 sprockets & I get the same rpm as you, 4800 @ 60 & every thing seems correct, maybe pamco's (hush) is off?
Chuck
Useful idiot
OK thanks, thats good info.
Chuck
Useful idiot
When I first got the MC the guages were slow from sitting. But they are fine now. No dmage to the guages and never torn appart. Its not a new problme. Just something I noticed when comparing to Pamcos chart. Maybe something is up with the chart and my guages are fine.
It does sound like yours is off. Here's a page you can enter your own numbers for wheel size, gearing, etc. It shows about 62 @ 4200 with your wheel/gearing .....
http://www.gearingcommander.com/
http://www.gearingcommander.com/
Chuck
Useful idiot
Great web page. Yes you are right. Its odd two of us have the same issue (me and bowhoc95). Or maybe its not.
I wonder if bowhoc95 has verified his speedometer. I am just guessing mine is pretty much right.
bowhoc95
bowhoc95
Running side by side verification is all.my speedo reads the same as other bikes & by "ear" the rpm's sound right..don't know if the tire is an issue..but I'm upper 4's at 60MPH
Tire size makes a big difference in the charts accuracy. Getting the tire circumference measurement correct and using that in your calculations is important.
As close as your speedo and tach are is close enough.
Don't worry about the little stuff, ride enjoy.
Leo
As close as your speedo and tach are is close enough.
Don't worry about the little stuff, ride enjoy.
Leo
bowhoc95
bowhoc95
I've been ok with the RPM's as is..This winter I will drop down to 17-32 combo to lower rpm's @ 60 mostly because I like the "Sound" better. Performance wise, great power @ the 5 rpm mark!
bowhoc95
bowhoc95
One of the intangible bonuses of the XS 650 is we can ALWAYS find something to discuss/figure out
