ATF can be a good solution and a cost effective one but you would be locked into a single viscosity. With our fork cartridges only requiring a few 100cc's, the cost of fork oil is minimal, plus one can exchange one weight to the next, with the next weight being compatible with the last.
If you start with ATF, and don't like the rebound or dampening, you would need to completely disassemble the forks to purge the ATF out of your cylinders. (If you wanted to go back to standard fork oil.)
Fork oil weights that were factory recommendations in the 70's and early 80's were meant for lighter riders of the day. the 1300 can easily tip the scales over 1,000 to 1,1000 lbs depending on rider/ riders weight with the basic weight of the bike.
One great add to our forks is adding RaceTech (Gold) Fork Emulators.
www.racetech.com
These are easy to install, with excellent tech support from these guys. (Not overly expensive) Its adding 21st century technology to our 20th century forks. They have a vintage bike area off of their street bike page.
If you choose the standard fork oil route, Bel Ray or PJ1 is a good choice.
When the forks are apart, don't forget to inspect/ replace the head bearings and look at the internal bronze bushings on the lower legs. Plus take some cotton to the upper chrome portion to make sure there is no pitting or damage. If you have an air crossover hose, those can become dry rotted over time, and may need to be replaced.
Regards.
T.
