关于打印连续走纸的问题

我用bs_300k的打印机,用delphi直接写并口,怎么走6-7张后,票就会往上跳一点,
奇怪
PrntTicketno:=Copy(ATicketno,(length(ATicketNo)-1),2);
  AMoney:=Num2CNum(StrToInt(AMoney));
  PrintChannel:=getSetupIni('Current','no');
  stationId:=getSetupIni('Current','id');
  Assignfile(f,'LPT1');
  rewrite(f);
  {初始化打印机}
 // Write(f,chr(27)+'@'); //chr(27)=ESC
  {设置汉字显示方式}
  //write(f,chr(28)+chr(ord('&'))); //chr(28)=FS
  {设定打印相对水平位置}
 // Write(f,chr(27)+chr(ord('\'))+chr($FF)+chr($00));  Write(f,chr(28)+chr(51)+chr(63));
  Write(f,chr(27)+chr(43)+chr(63));
  //设置高速打印
 // write(f,chr(28)+chr(ord('x'))+chr($01));
  Writeln(f);
  Writeln(f,'  '+stationid+'    '+PrintChannel+'      '+Auserid+'    '+PrntTicketno);
  Writeln(f);
  write(f,chr(27)+chr(ord('\'))+chr($CF)+chr($00));
  //放大金额字体
  Write(f,chr(28)+chr(ord('W'))+chr($01));
   Write(f, '      '+AMoney);
  //解除放大字体
  Write(f,Chr(28)+chr(ord('W'))+chr($00));  Writeln(f);
  Writeln(f);
  write(f,chr(27)+chr(ord('\'))+chr($CF)+chr($00));  Writeln(f,'  '+Apntdate+'    '+ApntTime);  Write(f,chr(27)+chr(ord('J'))+chr($FF));  Write(f,chr(11));
  flush(f);
  Closefile(f);