Rear Wheel Shudder

Hey guys, i'm having a weird problem with an au2 i just bought recently. Basically every now and then when i hit the accelerator from a standing start, i get some shudder from the rear wheels.

My brother says that he can see some smoke coming from the exhaust which makes me think it may be dirty injectors or faulty sparks??? I'm not that great with engines and don't have he right tools, so the best i can do is pull the leads off and they seem to be alrght.

Is this a normal problem with the au series??? As i said, i just bouht the thing and haven't had a chance to have it serviced properly.

Thanks in advance for any help/suggestions