Air filter caught fire and air box blown apart gilera runner

Hi, this has happened twice in a year now, I start the scooter and instantly air box goes bang, split apart and then smoke, I opened the air box,(what screws were left holding it together) and the air filter was almost completely burnt / singed, does anyone know why this could be happening? I have a Gilera runner 125, 2011.

 

Holy crap quiton!

Not sure what that would be. It wasn't in the sun all day was it? Maybe airfilter got so hot that when you started, some fuel or fumes leaked through and caught!

Someone more experienced should be along shortly to help better hopefully!

 

Hi, no not in sun all day, also, when servicing the scooter, the air filter is always singed/burnt, hopefully someone may know whats happening, thanks

 

a few possibles .

blowback from piston causing ignition of fumes in the filter , some fuel is blown out of the carb into the filter then sucked back in.

carb heater has gone wonkey and overheating to a point of combustion of fuel while in the manifold section,

blowback from a wonkey piston seal and failing reeds , the reeds should make a tight seal if they alow a leak past heat could start an ignition.

 

that sounds great, something I can look into , thanks,

 

2 stroke I take it?
Could be as above, could also be ignition timing way off for some reason

 

Hi, it's a four stroke

 

wow thats unusual for a thumper.

ok possible is the inlet value seat has failed and allowing combustion back up the carb to the filtering, but if this was the case you would be hearing tapping and finding starting very hard due to a loss of compression from valve seal failure

 

Water in the fuel or bad fuel, or bad mixture.

 

Hi all, I thought I would update. after this post, I noticed I had a very small water leak(a couple of drops a day) coming from the head gasket coolant jacket, the water was not mixing with oil or anything, but my scoot was getting more and more difficult to start, due to lack of pressure, and I started to get a bit of white smoke from exhaust, I took it to bike shop around June time, where they replaced all gaskets and oil piston rings etc, a complete top end clean, since then I have had no problems and the air filter has got no burn or singe marks, someone on here did mention lack of pressure could be causing the blow back from the carb and causing ignition, so I think that was the case, thanks for all replies, Q