Excellent point DK, and Felix, you be right as well... This is where I think we're running into a communication issue, let me try and clarify:
Backfire: A piston igniting Before Top Dead Center, BTDC, and actually driving the crank in the opposite direction as the engine should turn... Bad news on timing.
Knock: Anytime the fuel ignition doesn't correspond to, or is initiated by the spark plug. Over-compression, hot embers in the cylinder from carbon deposits, etc... Usually results in a back fire.
"Popping": When an internal combustion is running rich, and has excess, unburned fuel going through the engine and into a hot exhaust, and actually "exploding" in your exhaust. This is usually diagnosed if the engine runs fine and strong under hard excel, especially in the upper rev range, but starts "popping" when you come off the gas. More pops the harder you return the throttle to neutral. This is hard to explain without a video.. Damn I have to get a camera, and please bear with me. I really want to figure this out, so we have a good frame of reference for the future.
This, I think, is what Angel and Shady are speaking of. It can be remedied various ways, but what it comes down to, is the carbs don't correspond fast enough to the engine, and extra fuel is drawn through the engine. The exhaust is hot, and fuel eventually burns up in the exhaust. It's not necessarily a bad thing, nor will a little of it hurt your engine. If you come of the exhaust and your exhaust sounds like a machine gun, take it to somebody who can massage the carbs a bit better... Lean out the bottom end, and prolly top end, and adjust the needle accordingly to get a good balance.
DK, I especially want to thank you for the way you approached this discrepancy between you and I. I like, so many on here, are just trying to help, and I think (but what's my opinion worth?), that you are an A-spec example of a good communicator. This is my take on the situation, but I'm not an authority either, so what do you think of this? Where do we go from here to keep clarifying?
Oh, Shady and Angel, speak up. Is the "popping" what you ladies are experiencing? Help us out.
dknollRX7 said:
how do you figure....not trying to be argumentative, just curious. as I understand it, the backfire is caused by a predetonation which is also referred to as a knock. this situation occurs when the temperature in the combustion chamber surpasses the flashpoint of the mixture (a/f) and therefore ignites the mixture before it's predetermined time (power stroke via the spark plug). excessive temperatures are usually caused by a lean condition rather than a rich condition as the fuel actually cools the combustion chamber. I have seen misfires (no detonation at all either premature of from the spark plug) caused by a rich running engine, but not backfires. again, that's just how I understand it. let me know if you know something different that I may not.
