I was playing around with the main jet in my 1100 today (200 6 cyl). I have been running a #69. According to the Ford manual, it is supposed to be a #67. I installed a 67 and the car would hardly run while driving. It idled well but bucked and snorted while driving. Needless to say, I went back to the 69. I would not have thought a .002" difference would have made that much difference. Ive been chasing poor fuel mileage. I get 16 mpg average. It runs good and the spark plug color looks good so, the chase continues. ... Sure has me wanting to try a little larger jet size just to see how it runs though Unfortunately, 69 is the largest i have in the parts bin.