carb adjustment or timing?

BOH · Aug 25, 2019

My D14 runs real good right now. Plenty of power, starts good, idles good but.....when I idle it down from medium to high rpm to idle it pops, sometimes with a blue flame. I can start experimenting, but thought I'd ask your opinions first. Carb out of adjustment or timing a bit off? Thanks in advance. John

Janicholson · Aug 25, 2019

The engine is just fine. What is happening is that the high vacuum caused when idling down draws in extra fuel and this extra fuel in a partial vacuum
fails to burn in the cylinders and gets into the exhaust. In the exhaust pipe the temp is high enough for combustion, but there is still no oxygen. As
the rich fuel/exhaust gets air mixed with it at the tip of the muffler, it ignites and makes a pop, or flame. I would call that a sign of proper
adjustment, But not an analytical tool. Modern engines have decel fuel shutoff systems that litterally shut off the fuel leaving the idle ports and
main jets when letting off the gas. These ar usually computer controlled dynamic systems, not the carb on an old tractor. Jim

guido · Aug 25, 2019

Hello BOH,

X2 as Janicholson said NORMAL,

Guido.

Steve@Advance · Aug 25, 2019

If there any exhaust leaks it will draw air into the manifold, giving the unburned fuel just enough oxygen to reignite.

If it's otherwise running OK, I wouldn't worry too much about it.

BOH · Aug 25, 2019

Thanks Guys. I learned something today :lol: Sure am glad its nothing I need to adjust out, cause she is running so good. Thanks again John

carb adjustment or timing?

BOH

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Janicholson

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guido

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Steve@Advance

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BOH

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