[Farmall] Down hill foul

[Frank DeWitt]

Hi all

I have a 200 that always runs great,  EXCEPT  (You knew that was 
coming)  when I drive it to the parade

The route from my house to the parade is about 2 miles.  The first 
1/3 mile is down hill and two years running now it has fouled a plug 
on the down hill run.
I run it in gear to control the speed.  I have no way to trailer 
it.  Short of shutting off the gas and going down hill in gear with 
the engine spinning but not firing (That would be trickery) what can 
I do?  Hotter plugs? colder plugs?  other?

Thanks

Frank DeWitt