[mingmong]

Just performed an oil change. (Adjusted the rocker valve clearances too. Most where a little loose. Also cleaned and re-gapped spark plugs. They all looked pretty healthy, just a light dusting of carbon.) Filled it up again with oil and took it for a spin....and it runs really poorly! What have I done wrong? The engine stutters and backfires. Rev it up to 3K and things improved and it sounded nice but that's not fun in London traffic. Between 1-2K the engine backfires and stutters, put it in gear and it shudders and jumps all over the place. Managed to hobble home and checked all plug leads correctly seated and connected. (My thinking is it's not firing on all cylinders now but I'm open to alternative suggestions!) . On the plus point it's now got new oil and no leaks but whys it running so poorly? Any ideas? Cars a '77 C3.0 and WAS running sweetly till I fiddled with it. Cheers Mark