It seems my purchase of XR400 for the Trans Am Trail could have been a better one!!

I have now fixed my clutch and crossed the rockies, but am hanging around Moab , Utah because of a really unhealthy sounding top end rattle. Before I dismantle the bike I would like to know about any common problems or ideas.

The rattle happens predominantly at lower revs and seems to be a result of the front right valve, suggesting to me either a broken valve spring or problems with the decompression system. I have pretty much ruled out the valve spring issue and am fairly sure the cam chain isnt to blame.

The problem comes because i dont know muck about the decompression system fitted to kick start bikes.

The noise is a loud rattle from the top end of the engine. It makes the noise individually when I turn the engine over on the kickstart without the engine running as well as when its running normally.

When I remove the front right valve cover and turn over the engine I see a very odd cycle of events. The valve pushes and releases twice as you would expect (smoothly) but then a minor compression occurs hardly enough to open a valve and then as this releases the valve seems to hold down for a few fractions of a second before snapping back to the 'off cam' position. It seems to be this snapping back that is making my rattle. It is generally there, but every now and again on a slow tickover it sort of fades in and out in an intermittant manner.

I know diagnosing engine sounds over the net is a nightmare but do any of you have any ideas?

I really need to get this fixed and do some riding in some of the most spectacular desert/canyon scenery I have ever seen!!!!!

Many Thanks ( A tortured)

Dave