ETZ251 noise like knocking/pinking, but probably isnt

[keleto]

I still have a noise in my ETZ251 that sounds almost exactly like knocking/pinking, but probably isn't. Imagine marbles being shaken in a tin can. The noise only occurs between 4800 and 5500 rpm and will go with more or less throttle.

I have tried retarded ignition, colder plug, high octane fuel, octane booster and slightly richer mixture (all together) and the noise will still continue, which leads me to believe is is probably not actual knocking/pinking. Any suggestions ? My next theory would be small end but somehow that doesn't seem to match the symptoms.

I am going to try a different brand of points to see if that makes any difference, but I am not optimistic. Any suggestions ?

[vicar]

Sounds like a bit of piston slap, they all do it sir . Air cooled motor so it needs a bit of clearance due to expansion . It gets louder as the bore wears. I recently rebored my 251 and I can just about hear the piston rattling , before the reborn it was noticeable to my mates riding near me. Don't panic rebore with good quality piston and rings £62.

[keleto]

Thanks. Could be, but in my experience piston slap is normally loudest at idle and then smoothes out at higher revs, unless I am much mistaken, which I might be. Of course 2-strokes are always full of odd noises so I guess I will just have to see if it gets any worse. If not I guess it is just a characteristic of the bike.....

[DAVID THOMPSON]

my father said ...if its an engine and its not making a funny noise..
its either not running or its getting ready to blow up

dave

[Andy_C]

My ETZ 250 possibly makes similar noise.

I recently did some major work on the engine as I thought that the noise may have been clutch related, but it was not.

I know that bearings / piston bore clearance on mine are within the limits set in the handbook so nothing out of tolerance in that respect.

If yours is the same noise as mine makes it starts at around 3500 RPM up to the red line, but mine sounds a bit like a drumming noise. My conclusion is that is is induction noise as it sounds to be comming from the air filter area.

One solution I have and that is to ride wearing ear plugs, it's amazing how using ear plugs to keep out the noise makes the bike feel much smoother / better