TW125 won't start

[david k]

Hi,

I have recently changed the piston, and put on a replacement cylinder head on a 2004 TW 125, to overcome poor performance and low compression.

Now all is back together again, but the engine spins freely (until the battery wants a rest) but it will not catch.

I followed a workshop manual to the dot, so believe I got the timing correct, but just wonder.........is it possible to get the timing out by 180 degrees so the spark arrives at the wrong time?

I set the cranshaft marker to meet the 'point', the line on the cam chain cog is nearly at the 12 'O' clock position and both the inlet and outlet tappets are 'free' so I assume I am at TDC....but how can I tell if I've got it right?

Without the spark plug I can spin the motor on the starter and all seem to be moving fine inside.

I've not touched the carb, but notice that the spark plug appears dry even after numerous attempted starts.

Any advice would be gratefully received..........

David K

[Airhead]

Hi,

I have recently changed the piston, and put on a replacement cylinder head on a 2004 TW 125, to overcome poor performance and low compression.

Now all is back together again, but the engine spins freely (until the battery wants a rest) but it will not catch.

I followed a workshop manual to the dot, so believe I got the timing correct, but just wonder.........is it possible to get the timing out by 180 degrees so the spark arrives at the wrong time?

I set the cranshaft marker to meet the 'point', the line on the cam chain cog is nearly at the 12 'O' clock position and both the inlet and outlet tappets are 'free' so I assume I am at TDC....but how can I tell if I've got it right?

Without the spark plug I can spin the motor on the starter and all seem to be moving fine inside.

I've not touched the carb, but notice that the spark plug appears dry even after numerous attempted starts.

Any advice would be gratefully received..........

David K

Try this, its quick and easy

Take the plug out, squirt some oil in on top of the piston, this will help get a seal for compression, switch fuel to prime position, plug back in and try again

[david k]

Hi 'Oldgitonabike',

Many thanks for your guidance..it worked after a few coughs and splutters. I assume that was because the oil improved the compression?

Well it worked for about five minutes. There was a worrying noise, then it stopped. It would spin freely (in fact too freely) but would not ignite. I suspected fuelling problems, but further investigation found that the bolt securing my cylinder head camshaft sprocket was loose, and the timing chain had come off.

Good fortune befell me, and once reconnected and reset, the old bird restated better than before. It looks as if it was at TDC when the chain disengaged, saving the valves!

All in a days work...but thanks for your advice.

David K

[Airhead]

Hi 'Oldgitonabike',

Many thanks for your guidance..it worked after a few coughs and splutters. I assume that was because the oil improved the compression?

Well it worked for about five minutes. There was a worrying noise, then it stopped. It would spin freely (in fact too freely) but would not ignite. I suspected fuelling problems, but further investigation found that the bolt securing my cylinder head camshaft sprocket was loose, and the timing chain had come off.

Good fortune befell me, and once reconnected and reset, the old bird restated better than before. It looks as if it was at TDC when the chain disengaged, saving the valves!

All in a days work...but thanks for your advice.

David K

Wow, now that really was a strole of luck, nice to hear it

Yes the oil would give a better seal and improve compression, once its running, the increased engine speed plus the engines own oil supply would combine to keep it going.