Aprilia MX125 stops working

[mraprilia]

hi there, i recently bought a 2006 aprilia Mx 125 and it was running really well on the first day, but now it seems that after i open it up for a bit or ride up hills it just stops working, it doesnt even try ticking over as if theres no spark. after about 5-10 mins of trying to start it it runs for about a second then stops, then the second kick with no throttle will star it and it will run. ive checked the spark plug and it sparks nicely, theres no pressure in the fuel tank so the breather pipe is not blocked, the fuel runs out of the tank nicely with no blockages. i have also cleaned the air filter...Any ideas as to what could be causing this?
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ApriliaMX125

[stirlinggaz]

try using a brand new plug.
it might look ok when your sparking it out of the bike, but it may well be useless under load.
easy 4 quid thing to check.
cheers,
GAZ