Help! Can someone help me with a bit of advice. I have acquired a 1981 Honda CB750 which has had CB900 Air forks fitted. I need to know the best air pressure to use.
CB750FB Air assist forks
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I'd be tempted to leave them at zero and get the sag set up with a preload spacer and fork oil level instead. Reason is Boyles Law which states that for a fixed amount of a gas kept at a fixed temperature, P [pressure] and V [volume] are inversely proportional (while one doubles, the other halves). That means the air-spring rate gets very stiff very quickly, plus the volume is so small that it is very hard to set accurately.
'Hagon' and see if they supply a set of progressive fork springs for your model of forks it will solve loads of problems with setting the air assisted forks.
They changed the feed back of the front of my V Max which also has air assisted forks as standard, keeping the air pressures correct was a real bind.
assumption is the mother of all f*** ups.
As the above two posts say,
long term solution is probably best to stiffen up the forks by mechanical means, if they aren't actually leaking air and oil at present, then the kind of small volume hand air pump used to set mountain bike suspension (schrader type valve fitting) or available from some of the better bike accessories suppliers (possibly MnP, Busters, Demon Tweeks, or suspension specialists like MH, KAIS, Pro Action) is the most effective way to accurately set the pressure, ordinary footpumps, compressors, bicycle pumps will tend to release air on disconnection, making accuracy difficult.
Air assisted or fully air only suspension can work, but needs a fair bit of maintenance and upkeep, once bushes and seals start to wear much, pressure will revert to atmospheric quite quickly and damping oil may also leak out, whereas mechanical sprung will still hold ride height even if oil is leaking out.
Oh, and pressures, which is what you asked , should be online somewhere or in a Haynes, Clymer or Honda manual, don't think it'll be high though, maybe 10-20 psi, perhaps a google search is in order
And you should set pressures with weight off the front wheel, forks extended for accuracy.