Bouncing back end during wheeling.

The past few weeks I an learning to clutch my wr250x up on second gear. I am doing well but there a weird thing holding me back.. When I clutch it up most of the times the back tire starts bouncing like it loses grip.. So while the front tire goes up the back end shakes up and down.. I've never seen this before. I found out that maybe it's the road, maybe the tire temperature. I dont know. Maybe I am not heavy enough and bike loses grip?
It's a shame to be able to get it up and having this issue scaring me everytime.

I also get this "bouncing" of teh back tire when i accelerate a bit harder.. I suppose that situation "hurts" the bike huh ?
Anyone had the same problem ?
I could really use some enlightening.

First thing that comes to mind is the chain skipping over sprocket teeth under acceleration.

The stock sprockets, especially the stock rear sprocket that came on 2008 model bikes, is/are most known for this because the rubber damper ring bonded to it (it's an EPA-inspired noise damper) can actually lift the chain off the sprocket a bit.
This makes chain slack adjustment more finiky when wanting to clutch 'er up for a wheelie because if it's just a little bit more loose than the recommended slack spec, you can experience this skipping you're (probably) getting.
I also feel this then encourages riders to adjust their chains too tightly, another no-no.

The quick fix is to carefully check chain slack and adjust if it's too loose according to the specification.
My personal solution is to do away with the stock sprocket, altogether, and mount a real he-man sprocket to get both a sprocket without the damper, and one that's got a few more teeth on it in order to lower the gearing to something realistic for a 250cc bike.
If you go that route, you'll need a longer chain.
Well worth it, though.

YZEtc wrote:

First thing that comes to mind is the chain skipping over sprocket teeth under acceleration.

Yup.

What gearing you running? Stock? Count teeth if you don't know.

How old is bike? How many miles on current gearing set up? How old is chain?

How did you set chain tension?

Gearing is stock. and only has around 4000 miles on it.. Now i get this back wheelie hop also when accelerating a bit harder..
So it has nothing to do with the tires huh ?? i will have a look on the chain and let you know.. I just want to know that its not a matter of tires, bearings or something like that..

NikosKefGR wrote:

Gearing is stock. and only has around 4000 miles on it.. Now i get this back wheelie hop also when accelerating a bit harder..
So it has nothing to do with the tires huh ?? i will have a look on the chain and let you know.. I just want to know that its not a matter of tires, bearings or something like that..

Does your back sprocket look like this:



Does it have the "ring" or "gasket" that the red arrow is pointing to?