125 keeps cutting out when hot?

[h07swilkinson]

Hey guys,

My Lexmoto 125 bike keeps cutting out when it gets hot, last time I went to my mechanic he said something about a part bedding in quickly because it was rode too hard during the running in period, after my service the bike worked fine but after 200K it cut out after a fairly long ride for a 125 at high RPMs so i let it cool down and it was good to go again for a few miles then cut out again the distance it will travel gets shorter and shorter after letting it cool,, Any ideas ??

[Pjay]

Ignition coil?

[Teflon-Mike]

You say 'bedding in' Is this a 'brand new' unused, factory fresh bike? Or a used one that has had some major repairs like an engine rebuild?

If it's a brand new factory fresh bike, this shouldn't be your problem, it should be the dealer's who sold it to you... take it back, tell them to fix it.

If this is 'your' problem; Many faults can manifest themselves as power fade when the engine gets over hot, and lead eventually to motor conking.

First why is it getting hot? - Eliminate the simple & stupid first. It's probably an air cooled bike.

- Are the front cylinder fins clogged with mud from riding down contry lanes covered in ploughdropped mud, this time of year?

- Have you been thrashing it, in low gears, so engine's been working hard with little air flow to cool it?

Next; running hot, is usually a symptom of a weak mixture. That may be the carburettor isn't set up properly, or could be indicative of an air leak between carb and cylinder. Has any cylinder head or carb work been done recently?

Next; you say it was 'serviced'.. was it serviced properly? Who by?

Immediate suspect to leap to mind is the valve tappet clearances. If they are incorrect then as the engine gets hot, the clearances can grow or shrink as metal expands at different rates which can either stop the valves being fully opened, reducing power, and potentially causing conk, or holding the valve open, wasting compression, and helping the bike run hotter, loosing power until it conks.

Next up we get to the exhaust;

Exhausts that 'leak', either the gasket in the cylinder head is missing or not sealing, the exhaust itself rusted through, or been 'modified' so that it sounds louder, can cause the engine to run weak, and run hot and over heat.

Is the exhaust original? Is it 'sound'? Is it modified? Are gaskets present? Is there any signs of any leak?

Then, we get to the ignition;

Coil fault is a reasonable call, but not top of the list, they are usually one of the most reliable components, but they sit over hot engine, and can cause erratic running problems when they start to break down.

But first check is the spark plug, and to remove it, and have a look at the colour of the electrodes when the engine has 'conked' from hot running; colour or deposits on the spark plug can tell you what was going on in the pot before it conked.

OR, could be that the plug itself is buggered. Should have been swapped for new at service, but, a hot running engine can damage a plug and if not swapped when 'cause' of hot running, say a leaky carb manifold gasket, it can perpetuate the 'problem' you think should have been fixed.

Lots and lots of stuff there to be looking into... and that's 'just' the start I'm afraid. But I would strongly reccomend you buy the Haynes book of Chinky four-stroke 125's, that is a mine of useful info on these things, AND contains more complete diagnostic 'fault tree' faultfinding maps.

Add on Edd after looking at prior posts!!!

[Rogerborg]