Struggling to get my old loco running smoothly

[planty]

I got some help getting my MMS loco up and running after some cylinder changes (thanks mainly to DLRDan on here!), but after a summer of running it still has a problem.

The symptoms are this. It steams up fine (gas burner) and upon releasing the regulator it runs great for about 20-30 seconds and the slows to a halt (even off track). Close the regulator, allow the steam to build and it'll go through the same cycle.

Any ideas from experience of what might be causing this or things o can try to diagnose the problem?

[Big Jim]

It sounds like you are running out of steam, is the safety valve opening to early. Or are the cylinders to tight?

[DLRdan]

How much oil are you getting through ? If there are no visible leaks then it could be that there isn't enough oil going into the cylinders. Also try opening the regulator while in neutral to check for leaks in the reversing block. The other one is to listen to the exhaust beat, if its quite loud with no load (not on a rolling road) then there may be something in an axle bearing, I had a feather once that did a similar thing.