Having repacked my middle box ive still got a knock on the engine it seems to knock on the top of the stroke so im totaly baffled as there is no play in the big end or small end so all thats left is the piston to replace even though it looks ok . Ive read where a dt250 or a it250 piston will fit as they are the same as a ty250mono piston but a lot cheaper if so is there a certain year for each piston that will fit any help would be appreciated as im totaly baffaled !!!

You can have a knock just being lean on the pilot jet. You might try drilling out your own jet if you have a few spares.

Hi

I've been having the same problem on a Villiers 250 engine fitted with electronic ignition and a Mikuni 26mm carb (got fed up with the 'proper' Villiers carb p____g fuel everywhere. Pulls off the Bottom end beautifully but 'tinkles' loudly in the midrange (road work) and is very flat. Pressing the choke lever down cures this but the engine fluffs when the revs drop. I've been given the phone number of a specialist called Allens Carbs 01934 836733. Not had time to contact them yet but looking to reduce the flow of air through the emulsion tube (the bit that the needle moves through) in order to richen the mixture. Hope this phone number helps.

Paul

mine is definate knock once its gets warm i wiped the head of last night there is no play in the big end or small end the piston is quite tight in the bore i carnt get fela guage down past the rings the bore is spot less no marks are sign of wear it all looks pretty good yet it still knocks quite loud it even run nice with plenty of compresion .so could it be fuel, jetting, where i live theres no trials shops are any one with any real knowledge of this type of bike so im at a total loss .so what jetting would any one recomenden!!

i have just sorted my ty at last after all these months it was a blocked pilot jet ! it now running realy well im a mazed its still runing after riding rouned a wood for a day with it running so lean but seams to be ok these must be one tough bikes any way thanks for all the good advise over the months .