Bike jerking when revved hard.

[mattian]

I have a Kymco "Venox" 250 cc. There are not alot of these bikes around but, for reference you could compare this bike with the Honda "magna" 250. Its almost identical.
I have done about 10,000 kms so far and never had any problems with it, until now. Being only a 250 means that I often have to rev it hard out to get up to the speed limit if I am joining traffic from a stop sign, occasionaly, it has a tendency to jerk suddenly when given full throttle, especially in second and third gear. It tends to do it most when on a hill climb or even just a slight inline. Its a very short sudden jerk, like a sudden thrust forward, but only lasts less than a second but will do it 3 or 4 times in quick succession.
It doesn't happen all that often but, today it happened twice on my way home and, I am just wondering if someone could tell me the most likely cause.
Is it something I should be worried about?

[AllanB]

Probably just the turbo kicking in - ride the wave of power

When were the plugs last cleaned or changed?

[TimeOut]

If one of the sprockets is badly worn it could be jumping a tooth

[Rob Taylor]

If one of the sprockets is badly worn it could be jumping a tooth

My thought also,Worn Sprockets, so chain jumps a tooth.Replace both sprockets and chain.....Call in to a bike shop and they will check for you.If you are in Auckland go to KTL Motorcycles in Western Springs Road Morningside ,They are in the old Motohaus tyres Building ,ask for AJ real nice guys..

[piston broke]

does it leap ahead or drop out then catch again?
what about the plug leads or coil?
a short somewhere?

[mattian]

it leaps froward for a split second, almost like I have been hit from behind. Tends to do it 2 or 3 times in quick succesion. Didn't happen at all today though, even when I had to crank it real hard to get onto the motorway. Just seems to happen every so often.

[mattian]

Thanks alot guys, I will get the sprockets looked at too just in case. I am hoping it isn't worn sprokets, the bike is a 2007 model and I brought it brand new.

[theblacksmith]

I once had a suzuki that did this - found it was jumping from 3rd to 4rth gear and back -all in a split second. Only did it when in third though.I ended up changing the motor in the end so I cant tell you what the cause was.

[xwhatsit]

My ancient CB250RS has begun to do that in 1st gear. Not too fussed, as I'm building another engine up with a new gearbox in my spare time. Common opinion is that it's a worn gearbox, perhaps the gearbox bearings becoming too sloppy to hold everything in alignment when it's under maximum load.