Fire under the hood...what would cause it?


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By Big6ft6 - 16 Years Ago
So I'm considering cranking over the engine tonight to see what happens.  I've changed the oil/filter and turned the engine by hand to ensure all the valves are free.  I will disconnecte the fuel line before the fuel pump and dip it into a fresh can of gas.

However, the last time this car was run...a few years ago, they left the car run for a awahile and the car cuaght on fire under the hood.  My grandpa said the "float was stuck" in the carb.  The put out the fire, cleaned things up and replaced the melted wiring...and my understanding is the car ran fine afterwards...but????

But the more I'm thinking about this..how would a stuck float cause a fire?? If the float stuck withe the needle seated, where would the gas leak out?  From the float bowl gasket?  If the float stuck open the engine would just flood and stop right?

And why would the gas ignite? What started the fire?  Is the engine block hot enough on the outside to ignite spilled gas?  I can't see how gas would've hit the axhaust manifold.

I want to kind of have this figured out before I start the engine just to be prepared.

By Glen Henderson - 16 Years Ago
If you ever raised the hood at night on one of these old vehicles with bad plug wires, you would see a sight. I have seen some that look like a Christmas tree. Sparks everwhere! Just one source for a fire. Always a good idea to have someone standby with a good fire ext.
By crenwelge - 16 Years Ago
Fire is usually started from the carburetor. Did it have an air cleaner on it when it was started? In the the 50's air cleaners were also called flame arresters. It is not unusual for an old vehicle, especially one with valves that may be sticking to backfire though the carburetor. This is why I always recommend having a fire blanket around when starting an old engine. The sparkling from old wiring is a sight to watch, but I have never known a fire to start unless a puddle of gas was spilled and left where the spark could ignite it. The quickest way to extinguish fire in the carb is to open the throttle wide open and it will suck it down into the intake manifold. It is possible that wiring such as the starter circuit or the wires to the generator could have shorted, but that is very unlikely if the engine was running.
By Big6ft6 - 16 Years Ago
Thanks Kenneth, good tips to know.

I never heard of sucking the fire back down into the carb by opening the throttle, that makes sense.  I wasn't arround when the fire happened so I don't know if the air cleaner was on or not.

I hear a lot about sticking valves with a Y-block.  Why does a valve stick?  Valve springs seem pretty strong...it seems like it would take something pretty substantial to get the valve to stay open after the rocker arm has released...??

By aussiebill - 16 Years Ago
Nate, the valves can stick from sitting around for years due to being in the one spot and exposed to air entering through open valves, this can build a fine layer or film of rust? on the stem which makes it tight in the valve guide and holds it open, the same applies to the build up of old oil on the stems going hard. This why so many guys complain of dropped pushrods when starting old engine that has been sitting for years. Also old fuel loses its octane efficiency and turns back into a varnish like buildup and sticks everything. All this applies to all petrol engines, not  just your cusso. If using can of gas to start, try and do it outdoors and keep can far away from engine as possible, Do not! pour fuel down carb while engine is being cranked!!!! one stuck valve= backfire = fire, If carb starts to flood theres one time proven method to stop it prior to cleaning carb, hit the top of carb on top where the fuel line goes in  with a Wrench! Dont be afraid, Good luck. regards bill.
By John Mummert - 16 Years Ago
Depending on where the fire started there could be other causes. A stuck voltage regulator can feed battery current to ground and fry the wiring.

If the fire started on top of the engine the carb is a likely suspect.

I don't know if an ignition coil could get hot enough to puke oil and cause a fire. Sounds possible but never seen it happen, maybe if the key was left on.

What part of the wiring was replaced?