Vibration from 1980 Jota

mauricejota7604

mauricejota7604

Hero member
Location
Victoria Australia
Hi all looking for some ideas after tuning a mates 1980 S1 Jota and the bike seems to have developed an unusual vibration from the engine from idle right through the rev range feels quite unnatural although not severe I am not sure where to start, loose alternator?? the bike doesn't have to be moving for the vibration to start????????
Any Ideas?
M.
 
cam or primary chain overtensioned? does it whine?
have you refilled the sump with oil? (a former club chairman once forgot, his bike vibrated for a bit, felt all harsh, and then.......)
CLEM
 
Sounds ominous Maurice. Let someone else blow it up! Regards Pat
 
check the crank phasing
set your degree wheel up on No 2 cylinder
see where the outer two cylinders are in relation to No 2

I take it this is Tom's Jota ?

Good luck
Red
 
Thanks all (yes Toms bike) this vibration started Tom indicated after a fuel change in his town, no harsh riding, chains all ok plenty of oil carbs synchronizied valve clearances set, engine mounts all tight but this very annoying low frequency vibration occuring .
Red I will set up my degree wheel on the crank over the W/E.
Thanks all.
M.
 
G'day Maurice,

Don't know about Jotas but on an RGS the vibration can be caused by worn centre-stand bolts or a worn rubber block where the centre-stand sits up against the exhaust collector.

(Tom seems to be getting a bit of a reputation  :D)

Terry
 
Is this found by feel or sound,how are the tank rubber mounts.With luck something is rattling against something.Hows the exhaust mounts
 
Check the wheel weights are still there.Kinda odd its sudden onset without other symptoms.Have a look for a frozen link in the chain as well.Had another read and its doing it being revved on the stand in neutral.Hows the Jesus nut for tight
 
Take a good look at the chain. If it is worn unevenly,even without binding links,it can cause all sorts of weird sensations. I have a Triumph /Sprint that I chased an intermittant pulsing/surging type vibe on and it turned out to be the chain was stretched in a few places and different speeds would change the frequency and amplitude mostly depending on load.
 
Hi
The thing is it is stated that the vibration is there even when stationary,so it cant be the drive chain or wheels or bearings,was anything done that could have knocked the crank out of phase?check the flywheel/rotor,is there any damage?
Neale
 
Had a look at the alternator all tight had a look in the primary nothing loose although a fair bit of rock on the clutch basket as though there is a bit of clearance in those needle races, not this problem, left hand muffler has massive crack through it with tthe muffler almost separated near the collectot it is swinging around at the end, will check crank phase next.
 
My bike ran like a bag of shite when I had an exhaust manifold come loose, was really lumpy. Lovely and smooth when re-tightened.
You might be on the right track with the cracked exhaust.
 
Yes a cracked exhaust can definitely cause a vibration problem. You mentioned too that it started after a fill up? Have you replaced plugs and perhaps drained and tried fresh gas from a different source?
 
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