I started it 2 days ago and idled for about a minute then switched off to check oil level. later i've gone to start and no go. checked spark plug, no problem. when i kicked it again i had about 10 kicks then got off and 2 seconds later a huge firecracker sounding bang. very big bang when i was standing next to it. any suggestions.? have found that the fuel tap is leaking slightly but i believe it may have been doing it for a while. getting new rubber seal asap.