feed rate changing after spindle stop

Hello Chaps
I am using mach3 on a home made lathe.
I am having a problem with the feedrate
in the setup string i set f=.1 ( I am working in mm)
when i use G0 - the machine feeds at a reasonable fast speed
if i use g1 then the feedrate drops to about on trnth of what it is set at
do you have any ideas that i could follow to get it right??

regards

fred