A friend of mine picked up an Aprillia RS50 for his daughter which won’t start off the starter motor. You can bump start it with ease, it fires up straight away and runs lovely, but cranking it over on the starter motor you get absolutely nothing. Spark seeks ok cranking off starter motor and battery seems ok too. He tried jump starting it off another moped to give the battery a little boost just in case but that made no difference. Any ideas where to start looking please?
Is the ignition self generating or does it depend on the battery? If it needs the battery then possibly the starter is pulling the volts down.
We were thinking something like that but the spark seems ok. The battery was new a couple of months ago, it went flat trying to start it but its on a fresh charge now and still wont fire. Wondering about compression but cant see why it would bump start, run and idle fine, just not start off the starter if it was compression.
a real conundrum, since you describe spark is visible while attempting starter motor method. Might sound barmy, but if this were me, I would repeat test in the pitch dark with spark plug removed (although be careful of igniting fuel fumes, although highly unlikely) so that you can not only observe spark when starter operated, but also turn rear wheel in gear to compare spark*. Test 2 would be to fit plug and lead and look for arcing/escaped "spark" from plug cap, lead or coil while churning starter, as if leakage is occurring at anywhere other than spark plug tip, then bump starting might be enough to overcome this. *this is possibly precarious, but can usually be done with two people carefully balancing bike on sidestand, particularly 50cc. Also, is it the correct plug? - try and get a non-resistor equivalent of the correct plug.
Additionally to what @Chris says: Try leaving the plug in place and check to see if there is a spark with a spare plug. With the plug in place the starter will be under load, drawing more current and potentially reducing the power available for the ignition.
You'll need an analogue voltmeter to catch it in time - can you measure battery voltage while cranking to see how low it dips? This is assuming it's got an ECU that may be struggling to function due to lowered battery voltage... It's 12V, yes?? (haha - showing my age!) Is it practical to use jump leads to a car or bigger-bike battery and try it on the starter?
Thanks all, some good ideas there and definitely some more things to investigate. I’ll update once we’ve tried out the above. Much obliged
I think you will find that you need a top end rebuild ,bump starting turns it over way faster that on the starter,which it needs due to lack of compression ,easily checked with a compression gauge .These little engines get thrashed to death with minimal care :/
