Brett Stoner wrote:
> >>> Scott Lemser <ramman@mailexcite.com> 10/07 3:11 PM >>>
>
> >4 stroke engines can and do run backwards
<snip>
> Given that at the time the ignition is turned off the flywheel and the rest of the engine are still moving forward I can't imagine that a few fireings of one piston would be enough to overcome that momentum and reverse the direction. I dunno, I could be wrong, but it just doesn't make sense.
>
> Brett
This was more common when we had carburetors. As a foreign car mechanic during the mid 70's it was quite common for an engine to run on after the ignition was turned off. The ignition key was just that, it turned off the spark. As the engine slowed down and stopped it continued to pull a
perfect idle air/fuel mixture into the cylinders and out the exhaust system. When the engine came to a stop (rotational), one piston would come up on the compression stroke and a hot carbon spot would ignite the mixture in that cylinder, in turn forcing the piston back down in the opposite
direction. The engine would typically sputter for a second or two, then speed up on the air/fuel mixture it had left in the exhaust system and finally stop. It ran backwards! VW installed a fuel shut-off solenoid on their carburetors so when the ignition was turned off so was the fuel. It
helped though it wasn't perfect. My boss taught me to warm the engine up, take the air filter off, and while revving the engine pour a quart of water down the carburetor from a coke bottle. This steam cleaned the combustion areas of some of the carbon build up and worked for a while! If I
drove a vehicle that did this, I let the clutch out in gear as the engine stopped with my foot on the brake. Believe me, this was quite common. Today, with unleaded cleaner burning fuel, fuel injection, and computers, there is less carbon build up and the fuel is cut with the ignition so it
rarely happens.
George
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