Can anyone out there tell me step by step how to check, adjust and stiffen up the front forks on and 83 YZ 490

How do you check oil level?

Is the air attachment on top for bleeding off excess air or for stiffening?

Thanks in advance.

I don't have any specific knowledge for YZ490, but all damper rod forks are pretty much the same. The proper way is to get some stiffer fork springs. There are a few other things that you can do. You can add some air, but then you increase the chance of blowing the seals. You can put more oil in there, but that also comes at an increased risk of blowing the seals. Both those methods rely on the trapped air to stiffen things up.

The other thing is to add some preload with a spacer. This is normally done with a piece of PVC water pipe.

You can actually stiffen up the springs by cutting off a few coils and replacing the lost length with a spacer. While I have used a combination of a spacer, and increased oil level before, I have never cut a fork spring.

In all the bikes that I have had the oil was checked by removing the top cap, removing the spring, and letting the fork tube to go to the bottom of the slider. Then measure how far down the oil is from the top.

The guy that I inherited the bike from had put in a heavy wall steel pipe spacer on the right side and it looks like a stock thin wall spacer on the left. It looks like the spacer on the left is starting to be to small and allow the spring to travel over it.. .... I contacted the original owner and he said the same thing had happened to him originally on the right side. He put in a heavy wall spacer ( cheap tubing from home depot cut to the same length as the stock spacer) to replace it.

Will increasing the length of this spacer in effect stiffen the suspension?

Any idea what oil level should be?

Oil weight?

Oil level?

Air pressure? 0 psi ?, 5 psi? 10 PSI? What do you reccomend trying?

Thanks, Tim