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Why popping when lean???

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I cannot understand why lean makes popping.

I know rich … unburned fuel igniting in the exhaust, but lean???

Is there any difference in the fire colour that is exiting the exhaust when rich or lean? I have seen red fire on rich (I guess).

Thanks.

[ August 23, 2002, 03:00 PM: Message edited by: sabin ]

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This is what happens when the spark plug fails to ignite the charge in the cylinder. The engine continue to turn and dumps the unburned lean mix of fuel and too much air into the pipe. The next time the spark plug fires the mixture and the freakin' hot exhaust makes it into the pipe all the unburned stuff lites off. This is the popping noise.

A spark plug can fail to ignite a lean mixture. The 1800 degree flame front spilling out of the exhaust port into the pipe sure can ignite the lean stuff.

This lean condition happens when you chop the throttle at high RPM. The diaphram on the side of the Carb is supposed open a curcuit to prevent this over lean condition.

It also opens at idle sometimes causing a big change in mixture driving some of the jetting experts nuts wondering why the air screw and pilot jet settings never remain steady.

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Yeah...right. I now can go to sleep :)

Thanks for enlightening me!

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Originally posted by sabin:

I cannot understand why lean makes popping.

I know rich … unburned fuel igniting in the exhaust, but lean???

A lean mixture will result in unburnt O2 in the exhaust pipe and that is what is burning. If there were more fuel in the mixture all of the O2 would have burned.

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