Yes...all valves bent...smacked piston...good old interference engines. Started cranking really fast cause valves stuck open from overheat then...BAM...backfire out intake after only 15seconds of cranking...Head back off again. answering own question. Impossible to say. You need to find out why it backfired. Suggest you do a compression test.
A leaking spark plug wire can cause a backfire out of the intake, but the most common cause is a burned intake valve. A burnt intake valve will allow leakage during the compression stroke back through the intake causing a popping backfire out of the intake manifold.
A backfire is caused by a misfire... a cylinder fails to ignite the fuel which may cause a stutter, it may also cause a back fire due to it pushing that un-ignited fuel into your manifold where it then ignites from the heat of the other cylinders and boom you have a backfire...
If it is the intake manifold, there will be vacuum leaks, backfire, and poor performance. If it is the exhaust manifold, you will have loud exhaust noise which may warrant a citation - also, emissions control laws will be violated. Take the manifold ro a shop where it can be re-surfaced or try to find a product at your local auto parts store that will help seal the manifold. - Good luck.
The inlet manifold is leaking air, weakening the mixture, OR the engine timing/sparkplug electrode gap is outside specified limits.
I just had the intake manifold gasket replaced on my 96 century yesterday and my bill was $450 but my gasket was only leaking out. If its leaking into your oil it may be more.
It sounds to me like your ignition timing may be off. Is it also hard to start? Possibly a manifold vacuum leak. Check out your engines tune up.
having bad spark plugs could effect how the spark sparks and when it sparks. new plugs is never a bad idea
If it backfires while you are driving, the intake manifold bolts may be loose or the gasket may need to be replaced. If it backfires when you turn off the ignition, the fuel mixture is a little on the rich side.
Most likely you have a misfire caused by an intake manifold gasket leak at #1 cylinder. That or basic misfire stuff like spark plugs or ignition wires. Check the intake
It's probably leaking from a bad intake manifold gasket. You could be leaking from the heater hose that comes out of the firewall very close to the manifold. They sometimes leak there and drip down on the manifold. If it drips on a coil, it can eventually ruin the coil. It happened to me.
ok, is the backfire through the exhaust or inlet manifold? if its through the exhaust it means ur mixture is to rich, causing unburnt fuel to ignite in exhuast, if through inlet it is a lean backfire, either way if carby in good condition it sounds like mixture screw, to adjust, start car and get to operating temp, wind mixture screw in till car almost stalls then back out 1 and a quarter turns, that's a static point to go from. good luck
With Beetles backfiring usually means that (usable fuel) is too lean. The gas fails to burn efficiently and the unburned fuel mixture fills the exhaust system. Add a spark and it explodes. This can be from a vacuum leak from the carburetor/intake manifold flange or the manifold where attached to the cylinder head. This can be be from a number of things, these are just the most common.