CRF's Only Forums

I bought my bike about a month back and decided to change the piston as I was unsure when it was last done.i installed everything as it came apart, using timing marks on the right handside of the crank and the arrow on casing,and the lines on the cam shaft, so I'm pretty sure it is timed correctly.
there is a spark from the plug when rested on head casing(new plug fitted)and if I take the plug out the fuel mixture does fire from the cylinder so it seems to be getting fuel.
all bolts have been torqued to manual settings.
air filter is fitted and all manifold clips are tight so no air should be leaking.
I ordered the standard sized piston for the 76.8mm bore (76.78mm on the box)and the rings that came with it are the same as originals (size:76.80 on box)

the only actual difference I have noticed with the bike is that the red light next to the kill switch used to flicker when kicking but it no longer does. how ever I figure if it was the kill switch causing the problemvthe plug wouldn't spark, am I correct?

is there anyway to tell that the ignition timing is correct? I have checked the marks on the flywheel and the right hand mark lines up with the casing mark when the piston's at TDC which I think is correct as the spark fires just before TDC is this correct?

all plugs are connected and seem to be in good condition. the only one that is damaged is what I think is the thermostat which is a white coloured plug with a black cap and a gold thread which is located on the cylinder beneath the exhaust, but this was previously just taped up and the bike ran fine.

I havn't touched the valves at all as the bike was running fine before disassembly so I didn't want to disrupt anything I didn't need to.

sorry this is such a long post, I am just completely out of ideas and wanted to get as much information in as possible.

has fresh engine and trans oil and new filter.

I was unsure what the purpose of the centre groove is for on the piston as there is no ring for it,am I correct in that the order from the bottom is side rail ring, oil ring, side rail ring(in bottom groove with oil holes), top ring(in top groove with mark upwards)as this was how the original rings came off the piston that was in before.

the only thing I cant test at home is compression as I don't have a tester.

Anyone have any ideas whats stopping it from starting or had any similar problems? if not I will have to take it into the local bike garage but I really wanted to get it all going right myself just so I know what caused the problem. or put the original piston in and see if that changes anything...

Welcome to the site !!

The only thing i can come up with at the moment is its a ground issue , Check all the connectors , sometimes you will plug something back in , but not get it in till it snaps into position , and its enough to loose connection , where i would check is the wires to the stator and CDI , since you have spark , the coil should be ok as long as the spark is nice and blue , but the light not flashing would mean that its not getting a signal , so you have to trace backwards from the light to the sources

The cam could be 180' off

I managed to get it going again after 3 times stripping it down to the piston and triple checking everything it turns out it was just the temperature plug in the back of the cylinder that was broken. Although it was working when it was taped up before it mustn't have been getting a good connection and I'd spoke to an mx shop machanic and he said if that isn't working there's no way you'll get it running from cold. Bought a new plug put the head back on and she fires after 3 kicks thanks for the suggestions!