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I have recently fitted a SST 265 to my GP the engine is fitted with the Casa Expansion Box.
At certain revs I feel the resonanting through the seat and can feel it when I reach down and touch the bodywork.
As the revs increase it disappears.
I have checked usual suspects manifold touching frame,engine touching side panel and even loosened off the engine mount bolt,all to no avail.
I am wondering if it is simply the sound waves coming off the expansion box and causing the annoying tingling sensation through the scoot.
Has anyone any idea what it might be ?

Is your airscoop touching the seat frame? I have that problem with my GT240 where the scoop is in heavy contact with my Anciotti seat. Only a problem around 30 mph but very unpleasant

What engine mounts are you using ? some of the more expensive ones are reportedly very hard, causing vibration issues.

Assuming you have got a folding seat are the sides of your seat frame touching the frame loop? And have you used nylon washers when you fixed the seat? If you've got a bolted down one then they will vibrate if you've got a vibee engine but I would check for any contact points between the engine and the frame

coaster wrote:Is your airscoop touching the seat frame? I have that problem with my GT240 where the scoop is in heavy contact with my Anciotti seat. Only a problem around 30 mph but very unpleasant

I don’t have an air scoop mate

MickYork wrote:What engine mounts are you using ? some of the more expensive ones are reportedly very hard, causing vibration issues.

The mounts are Casa as supplied with the engine,I do not know if they are particularly hard mate.

missing lynx wrote:Assuming you have got a folding seat are the sides of your seat frame touching the frame loop? And have you used nylon washers when you fixed the seat? If you've got a bolted down one then they will vibrate if you've got a vibee engine but I would check for any contact points between the engine and the frame

Hi Mate
Fitted a replica seat from Beedspeed the rubber mounts where it touches the frame where horrible plastics and where actually taking the paint off so replaced them with some soft rubber I had lying around.All the bolts have rubber washers,but the vibration persists grrrr !

Get an air hawk seat cushion and pop it on top
of your exist seat , air cushion sections should
solve you feeling the Vibrations .

I had the sear off today and think I can improve the rubber washers by having them both nut and bolt side of the seat mount.

Rubber plumbing washers... Cheap as chips from all possible suppliers, use with/under all & any seat fittings...

With the scoot off the stand and you sat on it does any part touch the frame - you will need to get someone to look for you

Andy B.L.C. wrote:Rubber plumbing washers... Cheap as chips from all possible suppliers, use with/under all & any seat fittings...

You read my mind

Covboy wrote:With the scoot off the stand and you sat on it does any part touch the frame - you will need to get someone to look for you

Hi Covboy
I am sure nothing is touching the frame.It is hard to explain as it is not a vibration and disappears at high revs.
But is there at normal speeds.
I am going to try rubber tap washers top and bottom of seat fixing but feel it may need something softer.

Do the vibrations come through the handlebars too?

How is your exhaust mounted? What engine mounts do you have?

Found it !
I have a cheap Pegasus copy seat and the hinge pin is a very loose fit in the hinge.It is resonating like a bee in a jam jar !
Thanks for all your help and advice chaps.

Storkfoot wrote:Do the vibrations come through the handlebars too?

How is your exhaust mounted? What engine mounts do you have?

Bugger,thought I had found it with seat hinge issue but it’s still there. Engine mounts are the ones that came with the engine.
To answer your other question,there is no vibration through the handle bars.

My series 2 right hand rear floor board resonated at about 4500-5500 rpm when I scooped it out to allow the fitment of an expansion pipe. It was very annoying especially as everywhere I seemed to travel with my mates was 60mph which was right at the top end of the resonation. If I went faster the vibration stopped. I made a stiffener and bolted it to the underside of the floor board and it cured it.

ROClarke wrote:

Storkfoot wrote:Do the vibrations come through the handlebars too?

How is your exhaust mounted? What engine mounts do you have?

Bugger,thought I had found it with seat hinge issue but it’s still there. Engine mounts are the ones that came with the engine.
To answer your other question,there is no vibration through the handle bars.

I was thinking of loose forks but the vibes would come through the handlebars in that case.

I have read that some of the super engines have very firm mounts that may be more useful on a race track. I’d suggest you ask the engine supplier/ builder as such mounts on a really powerful engine may produce such vibrations at certain resonances.

If you could post some pictures of the mounts close up and the exhaust mounting points, maybe someone can comment further.

Storkfoot wrote:

ROClarke wrote:

Storkfoot wrote:Do the vibrations come through the handlebars too?

How is your exhaust mounted? What engine mounts do you have?

Bugger,thought I had found it with seat hinge issue but it’s still there. Engine mounts are the ones that came with the engine.
To answer your other question,there is no vibration through the handle bars.

I was thinking of loose forks but the vibes would come through the handlebars in that case.

I have read that some of the super engines have very firm mounts that may be more useful on a race track. I’d suggest you ask the engine supplier/ builder as such mounts on a really powerful engine may produce such vibrations at certain resonances.

If you could post some pictures of the mounts close up and the exhaust mounting points, maybe someone can comment further.

Yes I think you might be right about the silent blocks.
I spoke to JB tuning today and they sis said they fit BGM blocks to the engines they fit from CASA.
I think the race ones you are referring to are solid,mine have the normal 3 holes.
JB man said it is probably resonating off the expansion box which is what I have always had a suspicion of,so I am going to try wrapping the exhaust in exhaust wrap and stick sound deadening under the floor.