I have a 1995 Kobelco SK60 Mark III. I run a brush cutter on the unit and lately when the engine temp. gets up to operating the boom will not lift 1 time out of 5. If I let the control go to neutral and retry 9 out of 10 times it will then come up first try. IF I shut off the cutter while holding the control in the lift position the boom jumps up. In cold weather it takes 2 hours for this to start and in warm weather 30 minutes. It's definitely related to oil temp. I have had the valve block taken apart and no visible wear. My hydraulic guy is baffled and You cannot buy a new valve block from Kobelco. Gauges indicate all pressures are correct. So if heat is causing the valve to stick only in the boom lift is it possible it is a relief valve problem somewhere? What about control lever? It runs oil to controls. Pilot pressure is set at 400 psi. Have tried it as high as 800. All out of ideas
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