HI All, this is my first post and need some help. I have an 89 jeep with a 4.2 engine. I have put in a Howell injection system, which was very easy I might say. Runs great, but at idle it sounds like it has a miss and cleans up nicely once you get up in RPM's. Have been told to check the compression to see if I may have a burnt valve. Question is it four cranks of the engine and + or - 10 pounds around 150 pounds in each cylinder to still be good?