78 YZ400

[hardlydangerous]

Anyone got any tips or tricks for setting up the suspension on this thing?

I just removed the swing arm to replace the bearings. Man that shock is llike 4 feet long : and i did not really notice anything for adjustment. It's got a wierd nut on the top between the mount and the preload adjuster nut.

Anywho the manual say to use 10W-30 engine oil in the forks. There has to be something better then that

[OLDMXRACER 393]

Have you looked at this site? [Only registered and activated users can see links. ]
Yamaha sold a guage kit to set the nitrogen(?) pressure back in the day too. I've seen them on eBay. How about a picture of your RM 125?

[Shocknut]

Use a 10 or 15 wt fork oil. In fact Mobil 1 ATF will work perfect for your forks. That weird adjuster you speak of is your shock rebound adjuster.