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Re: [T3] Singel quit pack problem


On 23 Jun 99, at 7:08, Steven Ayres wrote:

> Assaf=> every time that I'm sliding downhill, I've got backfire.
> 
> I agree, this is caused by a leaky exhaust. 

I realize that this is the common answer that "everyone" gives, but 
it is not true. Backfire is caused by overrunning the engine with the 
throttle closed causing a mixture that is too lean to burn in the 
chamber to flow out into the muffler. The expansion into the exhaust 
system cools the mixture allowing some condensation, and richening. 
When you press down the throttle and get the cylinders to fire again 
(or when one just randomly manages to fire) the exiting exhaust gases 
ignite the mixture that is just outside the heads, causing backfire.
 
FI cars overcome this by shutting off the injectors on overrun, while 
some of the later carbed engines came with various devices to keep 
the throttle valve from closing all the way. This reduces engine 
braking but allows the mixture to be rich enough to burn properly.

Jim
-
*******************************
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
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