Yamaha IT Fork Air Valve Question

Hey guys,

So my roommate just picked up an '86 Yamaha IT 200S as an upgrade (and addition) to his '80 IT 125G. The bike is awesome. It's light and plush, but a little too soft for our (his) taste. I set the sag to his weight on the rear shock and set the rebound to soak up the rocks/roots up here in WA. As far as the forks go, it doesn't look like there's much adjustment besides the air valves on top of the fork caps. I've been racing motorcycles for most of my life and feel that I have a pretty good understanding of what's going on (mechanically) beneath me, but I am used to modern closed cartridge forks and not the conventional kind.

The air valves on top of the fork caps look just like the ones from an inner tube, so they are able to be pumped up or have air released. My question is: Does anyone have experience with using the air valves for tuning the forks? Yamaha recommends 0 psi, but it also says MAX 35 psi or so. Can you vary the air pressure in the fork to make them stiffer without fear of blowing out seals? 0 psi is WAYYYY too soft for any type of riding and pumping it up to 10 psi was like night and day. Any input would be much appreciated! Thanks! -Zach

the only tunability that fork has as far as damping is concerned will be via fork oil weight. You probably want to start with the correct amount of 10wt.

I used to run a little air pressure those old style non-cartridge forks all the time back in the 70s and 80s. If you have to go much past 10 psi to be satisfied in the ride , I'd suggest heavier springs if you can find any.

First thing though is fresh oil set at around 150mm.

Thanks for the response! Yeah the right fork leg has a leaky seal so once we replace that I'll put some fresh 10w in both, 6" from the top is what Dirt Rider recommended in their '85 review of the bike. I think eventually we will get heavier springs for it (he's 200lbs), I'll probably lower the pressure down to under 10psi just to be safe. Thanks for the info!

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