1997 Hyundai Excel Jerking ?

[Strawberry ??]

i have a 97 manual Hyundai excel, and all of a sudden it has started jerking really bad, only when i accelerate though not when shifting down in my gears. I have no clue what it is, as when i first go the car it was jerking a little bit but not much, so i got the spark plugs replaced, and it has driven perfectly until now, but its jerking really bad atm, what could it be ? i changed the spark plugs not long ago, do u think they may need to be replaced again?
How often should you change spark plugs? please help =[

[horst]

from horst
i have a similar problem,it will take time to find this problem,so far,i found that i have
no power on the spark plugs when the motor will not start or stops.
when it happens,i have push the starter for 5 - 10 minutes to get going.
hyundai dealer ,here in albion park ,nsw,has not found the problem.it has been with car since new.car has 25000 on the clock.