Steve Carey

Hey thanks for the replies, once we get my grandpa's loadstar international out of the shop, i'll get the mack in get brakes ordered and Ill start playing with that throttle.

Recently aquired a 76' Mack R600 with the inline 6 diesel. Dont know a whole lot about it but she lopes or surges like a horse. The rpms jump all over the place. I have asked numerous other people about them and they have no answer of what the problem is. Starts and runs fine if you either want to idle or keep your rpms at 2000, anything in between and the tach is jumping 500 rpms. I can hold the accelerator pedal fine but any bumps in the road and it goes to bucking. Even on some smooth roads when I want to hold only 1600 rpms, it just gets to loping again. Shes rough but I only use her for 40 hours a year and they are a long 40 hours with this engine lope.