Not that it really matters at this point, but I'm just curious. I pulled my motor to fix an oil leak and it just so happened the engine was getting like 10MPG w/ lockup.

When I pulled my cat off there was a chunk the size of a baseball by the outlet bouncing around. I'm guessing when it lined up right, it was really hurting my flow, possibly blocking a good bit.

Is it reasonable to assume this is why the spark plugs were always carbon covered and why nothing I did to the timing curve or settings ever got me better gas milage?

 

Try to breath throught a drinking straw. That should give you some idea!