Vibraaaatiiiiions..

[4everFJ]

So, before putting her up for winter, she rode quite smooth with no noticeable vibrations.

Now spring is here and she vibrates like crazy above 60 mph...

Obviously, it is something I have done to upset her...

During the winter, I treated her to the following:

New rear shock.
New chain and sprockets.
New wheel bearings.
Converted to needle roller bearings in the suspension linkage.
New cush drive.
Valves adjusted.
Carbs cleaned, adjusted and balanced.

Basically, I have had the whole rear end apart and changed/serviced all moving parts.

The vibrations are high frequency and can be felt in the whole bike. It is annoying to the point where you can't stand it for more than 5 minutes (feels like my feet starts to sleep..).

Any pointers where I should start looking?

[Alte Fahrt]

Did you have the rear wheel balanced after you installed the new sprocket?

[4everFJ]

Did you have the rear wheel balanced after you installed the new sprocket?

No, I have nerver had to do that when changing chain/sprockets.

Since the sprocket is at the centre og the wheel, I can't imagine it would have any influence om the balance, but I could be wrong...

[Harvy]

I have noticed that if the drive chain is too tight it can induce vibrations ----- maybe?

Harvy

[4everFJ]

I have noticed that if the drive chain is too tight it can induce vibrations ----- maybe?

Harvy

Checked, it is actually a little on the loose side.

I did another tests drive and if I bring it up to vibration speed and pull the clutch and close the throttle, the vibrations disappear. So, it is definitely coming from the engine.

Maybe holes in one of the carb diaphragms?

[FJmonkey]

It sounds like you narrowed it down to engine RPM relating to the vibration. Can you get the same vibration while sitting still and bringing the engine RPMs up?

[a.graham52]

Check for a source of transmission. Remember the operator is "isolated" from engine vibrations through rubber engine mounts, rubber fuel tank bushings, rubber bushings on the foot peg bolts (that's why the move when stepped on) and rubber pads on the pegs them selvs.

My bandit 1200 would vibe a lot with engine rpms due to a hard Corbin seat and also if I squeezed the side plastic too much with my legs it would induce a vibe.

Is the vibe rpm related (squeeze clutch and revv engine while coasting at cruise speed. Is it Trans gear related, does I'd in one gear vs another. Is it engine load sensitive, more throttle more vibe?

[Pat Conlon]

After a long layup, how about flat spots on the tires?

[rktmanfj]

Rear frame cradle bolts?   

[4everFJ]

OK, a little progress..

The FJ has been inactive for 4 months due to winter. This is normal here in cold Denmark and what I have always done with other bikes I have owned.

I add some fuel stabilizer in the last tank before winter and my bikes have always fired right up without problems when spring came.

Now, just to rule out the possibility, I drained the tank on the FJ and put in some fresh fuel. That made a big difference! Runs much smoother, but still some vibrations at certain rpm's.

Next step is to open the carbs and check carefully for diaphragm pinholes, since the vibrations sets in at rpm's above 5000.

[4everFJ]

Success 

Found a couple of pinholes in the diaphragms, patched them with liquid tape, balanced the carbs and now it runs smoother than ever 

[FJmonkey]

Excellent!