help!!!!

[Navin]

I changed the cas o ring and the heater hoses on my car today. after lots of swearing and scratching my head I got everything back together and all was good...............at first!!!!
When I started the car there was a loud tapping noise coming from the engine. I drove the car home which is about a mile away and the tapping seemed to stop I then went to get petrol and the car was very sluggish. If i try and accelerate the car would shudder and backfire!!!!!
Any ideas of what i'v done!!!!!!

[charged_rs]

its 1 of 2 things

when you removed the cas to change the oring , you and refitted it and upset the timing... get it checked out

or

you have the ht leads on in the wrong order