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Re: Backfire



On 21 Jul 98 at 11:51, T. A. Dapper wrote:

> I suggest that you get your VW on the road, run the engine up to
> about 3500 rpm in second gear, leave the clutch engaged and back off
> of the throttle - then measure to see if there is any excess fuel in
> the exhaust system.  This test works best with carburetor systems.

Of course, this is the classic backfire-causing situation.  Backing 
off on the throttle pumps the exhaust full of gas/air mix, none of 
which burned in the combustion chambers because the fuel/air ratio 
was wrong (just a natural problem with carbs.)  Then set a match to 
it when the you depress the throttle again and get one good power 
stroke that dumps a flame front out the exhaust port as the valve 
opens.

There's no mystery here, and no need for exhaust leaks.  It will 
happen in a perfectly sealed system because the air was pumped 
through the engine with the gas.

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