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Subject: Re: What's a Backfire

>From:    Harvey_Chao@smtp.svl.trw.com  

Date:    11/7/95  7:25 PM

My understanding is that the gross  causes are thus - 
o  Ignition timing off
o  Valve timing off
o  hot cylinder deposits igniting the mixture instead of the spark plug.
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Don't forget exhaust leaks! Remember, on the VW engines, there is some valve 
"overlap" with even the stock cam. (Overlap refers to a period where both valves 
are open.) Unburned fuel/air mixture is used to help force the spent gasses out 
to the exhaust. Allow some fresh air to enter this mixture...and under the right 
conditions (such as de-accelerating) you get BANG! Definitely not good for the 
EGR valve, if so equipped! On the type-I engines, the culprit is usually the 
joint between the heat exchanger and the muffler. Those little do-nuts sometimes 
don't seal properly, especially with aftermarket headers and the like.

TomC
tcarrington@tele-tv.com
88 Vanagon
65 Notchback
Wanna blown diesel Westy or sunroof (conversion project?)