Tacho / speedo mismatch

J

jota6297

New member
I have a 1979 Jota which shows 4100 rpm at 100klm/h (62 mph), this seems inaccurate to me.What revs should my engine be doing  with standard wheels tyres, 120/90-18 Bridgestone Batlax, at 100klm/h?
I wont be making any changes to the tacho as I have had it off numerous times but at least if I know it is running eg 30% fast I can make allowances.
Thanks in advance
 
hooksey said:
All depends what gear ya in !  ;) ;)
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Why would what you are wearing alter the rev counter? :D

                                                                    Dave
 
It depends weather your going up hill or down hill,or have a head wind or a tail wind.That makes as much sense as me getting consistent reading of this.Sometimes my 3C would show just under 4k at 100ks, and sometimes it would show 5k at 110ks and sometimes 5k would be 130ks not including needle wiggling.Not much help from me.
 
Thanks Cape, according to the the handy link you posted it looks like the tacho is running about 20% high. So 7200 rpm on the tacho relates to about 6000 actual engine revs, I think.
 
dja981 said:
Why would what you are wearing alter the rev counter? :D

                                                                    Dave
Click to expand...
Well if ya had on ya Tails and parachute pants im tippin ya would be catchin the breeze  :D

Go for the skin tight gear =  less drag  :o
Take a couple of teeth off the rear and give it the berries  8)
 
obviously never seen me in skin tight gear.
It has been suggested that at some stage the tacho may have been repaired with Honda bits as they ran the same instruments but  the internal gearing is different.
 
GPS satnavs are pretty accurate on speed, borrow one and check you speed first to be sure its not the speedo reading slow..
 
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