DT125 spark issue

calum17 · Brolly Dolly Joined: 25 Oct 2007 Karma :

Hi, im trying to get a dt125 sorted, but im having trouble getting the engine started - it used to run.
i've taken the spark plug out and held it against the cylinder head and kicked the bike with the kickstart (has no battery at the moment) and i cant get it to spark. is it liekly to just be the plug, even though it did run - or can i test anything else first.

im still unsure on how it works with no battery - it gets its power from the magneto, which turns with the enginem so no engine, no power, no spark ... yet it should start - how?!

moonzoomer · World Chat Champion Joined: 01 Jul 2012 Karma :

try a different plug and plug cap, or try removing the plugcap allowing the H.T lead to arch over onto any metal part of the engine or frame to test the H.T coil. Test the L.T input to the H.T coil by connecting the the L.T wire to a low wattage lamp (1-4 watt) and see if it lights up when you kick the bike. Also does the bike have a sidestand switch as they can give bother which can be cured by shorting the 2 wires at the switch.

calum17 · Brolly Dolly Joined: 25 Oct 2007 Karma :

thanks i'll try that.

it used to have a side stand switch - but thats been taken out at some point and the wires are now wrapped around eachother...

moonzoomer · World Chat Champion Joined: 01 Jul 2012 Karma :

Fizzer Thou · World Chat Champion Joined: 06 Aug 2011 Karma :

A friend had a similar problem with her DT125R where we found both the kill switch and the spark plug were giving problems.

The spark plug cap has an internal resistor that can give problems.If you have access to a multimeter the cap should read between 5-10k ohms.Check also that the end of the ignition lead has a good contact with the screw part of the plug cap.If in doubt,cut about 5mm off the end of the lead before reinstalling the plug cap.
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Boxing · World Chat Champion Joined: 13 Mar 2012 Karma :

Could be a number of things.

I had a 125CC off-road bike, and it wouldn't start for anything, no spark or anything.

I was puzzled, then realised the chain had fell off whilst riding before, striped it down and found out the magneto was damaged from the chain coming off and slamming into it. Looked for a replacement and it was something silly like £90 for a replacement.

Luckily, I had a scrap bike, which I got because the previous owner broke the clutch and kickstart shaft. Just simply swapped them over with the casing. Worked fine ever since, just not been bothered to touch the bike since repairing it, rode it once then left it sitting.