Extreme Vibtretion in midrange

[Haggard]

Hi fellas . Idid a saerch but couldnt find any thing that sounded as severe as what I'm up against.

Its a ht 70cc , starts good , idles fine , accelerates fine through low range , but when it hits a certain rpm, I swear , it durn near shakes you off the bike.
I've used several of these engines now and have seen anything even remotely close to the vibration this thing creates.
It doesnt start with a little vib. and get worse, it goes from fine to unridable in a split second , always at the (presumed) same rpm.
If I can get it up into the higher range , it smoothes out a bit but is still horrible.
Any suggestions???
Thanks in advance

 

[BlueCollarBikes]

Hi fellas . Idid a saerch but couldnt find any thing that sounded as severe as what I'm up against.

Its a ht 70cc , starts good , idles fine , accelerates fine through low range , but when it hits a certain rpm, I swear , it durn near shakes you off the bike.
I've used several of these engines now and have seen anything even remotely close to the vibration this thing creates.
It doesnt start with a little vib. and get worse, it goes from fine to unridable in a split second , always at the (presumed) same rpm.
If I can get it up into the higher range , it smoothes out a bit but is still horrible.
Any suggestions???
Thanks in advance

Could be many things.
One thing I would check First is Lose motor.
I have had this same situation only to find the motor to the frame bolts had loosened up.

Bob.

 

[Large Filipino]

Maybe it's a fluke engine with the counter weights off?
WELCOME BACK HAGGARD!!

 

[fatboy67]

Maybe your flywheel has come loose.