MEga256 clone responding slow

I had used the Mega256 SCh to build my board, Using Arduino mega as ISP to burn sketch, I had loaded boot loader from Arduino IDE. and when I downloaded the blink led code. Led responding slow. same with Serial code. delay of 100 acting as of 1000 on my board in code baud rate in 9600 but i am getting proper value when i set 4800 in serial monitor. Can any one point out the problem Thanks

If your ans regarding to fuse than please specify which one and also which fuse has to set to use external osc.

Look at boards.txt for the Mega2560 board, the fuse settings you need are there.
Can verify them with Nick Gammon's tool here:

I had match fuse setting nothing changed.

Also can you specify the fuse which decide weather to use internal or external oscillator.

Also i am unable to program the mega via usb but getting response when using the serial monitor

DFU file was selected properly.

My boards.txt



default board may be overridden by the cpu menu

Table 30-5. Low Fuse Byte:
            Bit No Description             Default Value
CKDIV8(4) 7   Divide clock by 8     0 (programmed)
CKOUT(3)  6   Clock output            1 (unprogrammed)
SUT1         5   Select start-up time  1 (unprogrammed)(1)
SUT0         4   Select start-up time  0 (programmed)(1)
CKSEL3      3   Select Clock source  0 (programmed)(2)
CKSEL2      2   Select Clock source  0 (programmed)(2)
CKSEL1      1   Select Clock source  1 (unprogrammed)(2)
CKSEL0      0   Select Clock source  0 (programmed)(2)

2. The default setting of CKSEL3:0 results in internal RC Oscillator @ 8MHz. See Table 10-1 on page 40 for details.

Table 10-1
Device Clocking Options Select(1)
Device Clocking Option              CKSEL3:0
Low Power Crystal Oscillator       1111 - 1000
Full Swing Crystal Oscillator        0111 - 0110
Low Frequency Crystal Oscillator 0101 - 0100
Internal 128kHz RC Oscillator     0011
Calibrated Internal RC Oscillator 0010
External Clock                           0000
Reserved                                   0001

Note: 1. For all fuses “1” means unprogrammed while “0” means programmed.