I have a 2" honda water pump that only pulls a 4 to 5 metre head, its rated at a 8 metre head, was working fine but last week it started to loose pressure when watering, Pump does not change revs at all  but water pressure from the watering hose goes from a 3 metre squirt for a few minutes to  a 30cm dribble for a few minutes, this repeats continously while the pump is running between the 2 different pressures.  With all the heat I have had to have 2000 ltrs added to the well everytime I want to water as the well runs dry over night(water table has dropped due to other doing heavy watering), this problem  started happening after the first time the well ran dry but once we had the 2000 ltrs added the pump started working  ok before this started happening so it has me puzzled, removed the screw cap and made sure the priming area was full and cap securely back on but have had to refill the priming area the next day  before use. I am not mechanical minded apart from some basic stuff so any suggestions as to why this is happening would be appreciated, pump was serviced around 6 months back so I know it should be ok, thought possibly air in the sytem but not really sure as I cant understand why  the pressure changes keep happening at similar times continually.

Sounds like the well is running out of water. Pump drops pressure as air is introduced due low water, then as well refills through seepage from walls, picks back up again to normal pressure. Suggest to reduce the flow from the pump to balance water inflow to water pumped out. Happens this time of year for me all the time. Water table drops during the hot season.

Have a look at your foot valve, if you are priming the pump all the time, that could be blocked or a weak spring /seal, I have had that problems with our pump, also check inlet pipe connections, any leaks in the suction pipe the water will not flow properly. 

thanks guys, will check it out, also realized that the 2" tube into the well may not be sitting under water continually, the filter is only plastic so has a tendency t float and the weight to hold it down had come away so wll try attaching another weight to ensure the end remians under water, really appreciate the replies

Finally got it working properly yesterday, after checking per what you have said I did find the problems and corrected them, pump is now working fine again.