Try changing your coil & purlpe resistance wire that runs from the coil to the back of the choke. Also pull the plate in the distribributor under the point and spray some wd 40 on the springs and clean up any rust to make sure as you twist the pate it springs back and is free working so your spark advance can work.

Don't do the following until you have corrected your problem.

The best thing that I did to my 470 was to do away with the points and put on an electronic conversion kit. She starts with the touch of the key and has held timing for the past 4 seasons.

Good Luck
gjgomes
Try this site, I learned alot about my motor from here.
@ www.boatfix.com