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My shock pump loses a bit of air as I attach and remove, making setting up a shock and forks a bit hit and miss.
Anyone know of any good shock pumps capable of 300psi and not losing any pressure please?
It shouldn't. The air you hear releasing is the air in the pump not that from the shock body coming out. When you reattach the pump you have to fill the chamber of the pump to get a reading hence it comes out at a lower level than that which you left it at.
Are you sure it's not just this?
Try one of these:
http://www.wiggle.co.uk/p/cycle/7/Topeak_Pressure-Rite_Connector/5360017387/
quite a bit cheaper. 😉
I use the Topeak check valve. Does the job nicely I think.
Beto's pump is well priced and works brilliantly, no contest really IMO.
http://www.highonbikes.com/beto-mp-035-mtb-suspension-fork-shock-pump.html
No quality shock pump should actually lose air from the spring.
As above, your pump is prob fine. You connect pump, shock loses 5 to 10 PSI as it fills the pump. If you remove the pump, the hiss is from the pump, not the shock, so the last reading from the gauge is correct. If you connect the shock twice without adding any air, the difference in the two pressures is the amount you lose by connecting the pump, so you can take this into account in future when making adjustments.