Rhythmic light vibration through the handlebars when engine cold - 04 1150GSA

[Pete D]

Chaps

A slightly odd one...

Before my 1150GSA (Twin Spark) is fully warm, but with Fast Idle off, I have recently noticed a rhythmic vibration (about one shake every 2 seconds), whilst holding a constant or slightly trailing throttle at about 2500 RPM, through the bars of the bike.

Strangely, when warm, the bike is as smooth as silk in the same throttle range (and indeed throughout the rest).

I'm stumped for a reason...initially thought throttle bodies out of balance, but the subsequent smooth behaviour makes me discount that....

Perhaps a coil stick on the way out.....?

Any thoughts?

Cheers

Pete

 

[mspenz]

I have the same age GSA and it does the rhythmic vibe as well....but only in 4th gear and hot or cold!! I've come to the conclusion after 6500mls that there is nothing wrong with the bike so I live with it and just accelerate through the odd spot!

 

[Pete D]

Aha. Already doing the same re avoiding that range, but none of my other GSs have done it....1100, 1150 or 1200. How odd; this is my only 1150 GSA example though.

Cheers....guess this falls under 'character'....


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[warmshed]

Do you think it could be flaky bearings? if so would it only affect 4th gear?, maybe someone could enlighten us.

 

[Pauly S]

They all do it in 4th gear, only the gsas though, its to do with an alignment of the all the drivetrain,the crank and flywheel,gearbox and fd,the only way I can explain it, its like a total eclipse of the sun,when all the planets whirr round,after so many cycles the moon masks the sun,its the same with the gsa in 4th,every 75yds or so,thrummmm,thrummm thrummm,doesn't do it in any other gear.I had a nearly new 115gsa years ago, I even changed the gearbox, no difference, its the way they are.If you ride the std 1150 it doesn't do it, the gear ratios are different.

 

[Pete D]

On closer and more diligent analysis, mine is also only apparent in 4th, but still only really noticeable when the motor is warming. Heartened by the explanation above. I shall worry no more....

Cheers


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[mspenz]

They all do it in 4th gear, only the gsas though, its to do with an alignment of the all the drivetrain,the crank and flywheel,gearbox and fd,the only way I can explain it, its like a total eclipse of the sun,when all the planets whirr round,after so many cycles the moon masks the sun,its the same with the gsa in 4th,every 75yds or so,thrummmm,thrummm thrummm,doesn't do it in any other gear.I had a nearly new 115gsa years ago, I even changed the gearbox, no difference, its the way they are.If you ride the std 1150 it doesn't do it, the gear ratios are different.

I knew there would be a simple explanation, it's all to do with the tides

 

[Pauly S]

On closer and more diligent analysis, mine is also only apparent in 4th, but still only really noticeable when the motor is warming. Heartened by the explanation above. I shall worry no more....

Cheers


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try cruising along in 4th, about 30-40mph I seem to recall, with a very light throttle,it seems to be when all the gears,cogs,fd,driveshaft all go into a spassy at once.Its called a harmonic vibration ,then at the same road speed, try changing down or up the box, at the same speed, it wont do it, only in fourth.Let me know.
The std gs wont do because the gsa has a close ratio box, whereas the road bike has the std gears much wider apart.

 

[Pete D]

Tried exactly that last week.....spot on - exactly as you said. Guess it really is a 'feature'....

Cheers


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[Pauly S]

Tried exactly that last week.....spot on - exactly as you said. Guess it really is a 'feature'....

Cheers


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I used it to remind me I was in 4th gear,so need to look at the RID.

 

[mspenz]

I used it to remind me I was in 4th gear,so need to look at the RID.

Yup, me too! If had gotten any worse then I might be more concerned but I'm so used to it now and just feel that it's (yet another) characteristic