OMFG - K100 catches fire

[BlueK11LT]

The K100 owned by my friend that I mentioned in my previous thread http://www.motobrick.com/index.php/topic,12718.0.html caught fire as he attempted to start it up.SHIT
After fitting the new fuel pump assembley and putting a few litres of petrol in the tank,he pressed the start button for a few seconds,the bike seemed to start firing up but suddenly flames shot out from under the tank,he quickly pushed the bike out of his garage and managed to get his garden hose to extinguish the fire,but not before damage was done - much of the wiring harness under the tank has had its insulation melted,the air filter intake duct has melted,the choke and throttle cables have seized solid presumably because the outer plastic has melted then  cooled down again and stuck hard around the inner cables..Theres a fair amount of soot covering most of the mid section of the bike including the tank which hopefully should clean and polish up ok.Luckily all the plastics surrounding the radiator and the side panels were not on the bike.
A strange result of the fire is that the starter motor now spins all the time the ignition is turned on ,any ideas about that anyone?.
On examination it was determined that petrol had leaked out of the pipe where it leaves the tank to go to the injectors,and accumulated on top of the crankcases i think he may have neglected to tighten the clip properly 
At the moment we are at a bit of a loss about what ignited the leaked petrol as he spun the starter,i think its possible there may have been a backfire through the air filter or there was some rogue spark somewhere under the tank,  :idunno:any suggestions greatly recieved
will post some pics later.
Thanks
Dave

[BlueK11LT]

Hi Johnny - well,we know that at least the main wiring harness,the injector harness,the cables I mentioned and the intake duct need replacing which we are in the process of doing,but apart from the mess that the soot has made everything else seems intact,i guess it could have been much worse.

[natalena]

greetings...

we do not speculate here at the world famous motobrick.com...

we are based in reality and facts...

j o

I half expected a flittering, seizure inducing Eyeball Pizza meme. ;)
Excellent self-control.

[daveson]

 Maybe there was a short in the wires,  causing the spark, or loose connection.

Was the battery fully charged?
There is a good chance the tank was leaking.
My '84 model sat for ten years and has at least ten holes under the tank, most of them after I cleaned it.

Melted wires could be bypassing the start button, causing your new problem.

Maybe look for a cheap brick for parts.

[Scott_]

Maybe look for a cheap brick for parts.

Or find another bike and strip this one down for parts.......

[GaryFrank]

I’ve just finished rewiring my burnt out K100.... pretty straight forward if you have a decent wiring diagram

[Laitch]

On examination it was determined that petrol had leaked out of the pipe where it leaves the tank to go to the injectors,and accumulated on top of the crankcases i think he may have neglected to tighten the clip properly 
. . . i think its possible there may have been a backfire through the air filter or there was some rogue spark somewhere under the tank,  any suggestions greatly recieved . . .

A loose ground connection might spark. The starter motor itself could have been the source of ignition. Speculation is useless at this point. An accumulating pool of fuel emits vapor that can find its way to many possible ignition sources on an elderly moto.

Attention being paid at reassembly of fuel system components is a critical task. Having a fire extinguisher of the type for gasoline and electrical fires within reach is important when working on a moto. Although water can smother a gasoline fire, it can also scatter flaming fuel that might start secondary fires. That didn't happen in this case, so rehabilitation of the moto is possible without first rehabilitating the rider or the building.

He is not the first here to restore a fire-damaged moto. There are threads here that might help. This is one of them.

[mw074]

 I picked up a K75S that had burned just to use as a parts bike. I wound up rebuilding it and it was one of the best K75's that I ever owned. It required quite a bit of work and meticulous inspection of the entire bike. Parts not even close to the fire ( fuel rail ) had heat damage. With all the de-looping going on, finding repair parts shouldn't be too difficult. Enjoy rebuilding it and be happy with the massive amount of K bike skill and knowledge that you will acquire.

[Soggz]

Loose spark plug cap. If the petrol was on top of the crankcase. Could’ve jumped up to it. It don’t take much fumes and spark.