Help me out guys please

I thought i was 18 stone. I was wrong.
I was interested to find out if me being a fat nacker at 19.5 stone

would have a huge affect on a 0-60 dash. Don't worry I know they're useless anyway cos of al the different variables but was interested to know what this extra weight would do to overall acceleration after reading some interesting physics theory. Especially as I know there are a few physics whizzes on 'ere

So.
Acceleration = Force / Mass (A = F/M)
If we say that acceleration is 100 the we ca get an idea of an exact reduction in acceleration in percentage form. And 19.5 stone is our mass. So our force just be 1950. So. . .
100 = 1950 / 19.5
If we reduce the mass to a more normal (and healthy

) 13 stone our formula becomes. . .
150 = 1950 / 13
Meaning acceleration has increased by 50%
Now I'm sure there's some flaws in my formulas so if anyone can correct my figures and work out with the formula what an extra 6 stone would do in real terms we can have an excellent physics discussion.
(Can you tell that swmbo is forcing me to take her out this morning and I can't get my paws on my welder yet ?

)