Speedo Accuracy?

[Spudiator]

This is a bit of an odd one, I was starting to think it was because of the different riding position distorting my judgement, but I doubt it, I think my speedo is majorly under-judging my actual speed. It seems like it's been doing it all along, whenever I'm riding I always feel like I'm going faster than the speedo says, when I pass by the speed detector signs (the ones that just show the 30 zone sign and a GATSO sign in LEDs) doing dead-on 30 I'm setting them off, and when I'm following other traffic I'm constantly finding myself being told I'm doing only about 15-20 in 30 zones when it feels far faster than that to me. Is this a common issue or have I just got a knackered speedo?

[leopard_pagan]

has it been dismantled by any chance?
reason i ask is when you change the face to a MPH one (is 1 fitted/) you have to pop off the needle.
soooo many people never think to take note of where the needle sits relaxed, just just assume its next to the stop peg.. it sits relaxed aprox 1/2 a cm past the stop peg. you have to lift it back over the stop peg.

=wrong set needle can give you wrong readings.
also does your bike have non-standard sprockets teeth count?
as the speedo runs off the front sprocket, changing the teeth will change the speedo.
dont forget these bikes are old.....

[Spudiator]

Honestly? I've no idea, I've only had the bike a week, I did take the speedo apart myself the other day to see the inside and see if it was possible to take the restrictor disk out myself (not something I felt comfortable meddling with in the end), but it was already reading inaccurately before then anyway. If the needle is in the wrong place surely lifting the needle over the stop peg would just get it stuck, wouldn't it? How will I know if I have the wrong front sprcket on?

[leopard_pagan]

get in contact with who you bought the bike from ASAP and ask. most people dont mind giving you extra history. if bought from a bike shop. ask them to give you prev owners details....
i buggered my speedo up fishing the disk out. now on my 3rd speedo! they are sensitive bits of kit and dont like being played with. i take my time and am very careful...

on the dial theres the stop peg....
your needle should sit to the left of the peg as you look down at the speedo reading as normal.
when one removes the dial for a better looking one or a plain MPH one. you have to remove the needle. before you do you gently lift the needle over the stop peg so it relaxes past the peg. its THAT position you must re-fit the needle to and gently pop it back over the stop peg when done.
if you didnt originally do that, it will be hard to figure out how far it originally relaxed.

BUT i think its more a case of the front sprocket not being standard. count how many teeth it has and post up the amount. someone will tell you if its normal or not.

[SHimmer45]

if the speedo is on its way out or the drive from the front sprocket is iffy then they are gonna cause miss reading.

also if some 1 has changed the gearing it will under or over read depending on which way they have gone.
i only had my 400 for 18months and hand to change the sprocket pic up twice along with the cable and the speedo assembly itself