Hi Stuart,
As Ron and Colin have said have you set up the ESC correctly? You can reset the Viper as follows ESC SET-UP
Before beginning set-up you need to connect up your VIPER ESC as in Fig.1.(When plugging the ESC’s receiver lead into the receiver make sure that the signal wire - orange - is facing inwards). Calibrating the ESC to your transmitter
Now that you have installed your VIPER ESC in your model you need to set the ESC so that it responds to your transmitter.
1. Switch on your transmitter and ensure the throttle control and throttle trim are in the neutral position.
2. Plug your VIPER ESC into your battery pack and turn the ESC on with on/off switch. (The red & green LED’s will flash for 2 seconds - This is the set-up window, if you press the button whilst the LED’s are flashing you enter set-up, if you let the LED’s flash for 2 seconds then stop, the ESC will operate with previously input set up values.) NOTE: If you have removed the factory fitted battery connector, (see warranty) ensure polarity is correct.
NOTE2: If LED’s do not flash but instead there is a solid red LED this indicates no signal, check transmitter is turned on & that the receiver lead is correctly plugged into the receiver.
3. Whilst the LED’s are still flashing, press the set button, this will set your neutral position, the green LED will come on.
4. Push the throttle control to the full forward position and return to the neutral position, (This has set maximum forward speed point) the red LED will come on.
5. Pull the throttle control to the full reverse/astern position and return to the neutral position. (This has set the maximum brake/reverse/astern point), this is directly from the Mtroniks manual. Hopefully this will work perfectly for you as I had the same problem with Javelin and this sorted it out .