Weird "knock" sound from engine...

[ridetheworld]

Hi all,

Touring around south America on a newish 250XR Tornado Honda, it has around 14,000k on the clock. I recently had it serviced by recommended mechanic in Sucre, they checked the valves. I have done around 1,000k since. PS they changed the sparkplug as well.

In the past two days I noticed quite a distinct "knock" sound, this apparently only happens 1, when I start the bike, it sounds like it is comnig from the top part of the engine. And it doesnt always happen, and if I give it revs it sounds fine, however 2, if the bike is idling and I just give rev it a little bit, i.e. pull and let go off the throttle just a little, every so often I hear quite a loud knock. Sometimes it cuts out afterward.

It only seems to happen when I give it gas when the bike is idling. Lately I messed around with the pilot fuel screw on the carb to try to readjust for the decrease in altitude, so I screwed it out. But other than that, no one has changed anything on the bike since its last service.

Having read up a little, I see that a too-lean mix can cause both engine knock (which I presume this is what it is?) and pre-ingition. I am hoping it is this and nothing else, any of this sound familiar?

One thing I am rather concerned about is maybe they didnt tighten something when they checked the values. From memory the values were okay and did not need adjustment. I mean, if there was something wrong internally I assume the engine would either be ****ed by now and not running at all?

Any ideas? Driving around the bike runs just fine, and like I say, seems to be only happening when giving it a little gas from idle or when starting. As usual, any suggestions would be great, as I am feeling a bit worried.

Many thanks,
Rtw

EDIT; I just tried to it again and now can't get it to happen, difference obviously being before it was hot and now its cold... Any help? :confused