Work from the outside in, simplest first:
1) Supply pressure: fluctuation shows up directly as volume variation; check the regulator and reservoir level first.
2) Needle: wear, deformation or partial clogging drifts the flow; swap in an identical needle to compare.
3) Bubbles and residue: incomplete de-gassing or cured residue in the flow path causes intermittent dispensing.
4) Stator and seals: wear after long service causes metering deviation - a normal consumable replacement.
If it is still unstable, send us your volume test records and we will help analyse.
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