198 vs. 225 revisited

Anyone have any expierience/info on MPG comparisons between 198 + 225? I think I will do a quick re-ring to replace the oil burner I've got now. Started taking spare 225 + 198 apart and the inside of the 198 looks as clean as an OR.

So I got to thinking...What was the thought process in producing the 198? Why was it made for only 2 years? Did it absolutely suck?