RE: Backfire

[Gurrola_J <Gurrola_J@BLS.GOV>]

I think that the reason that people believe that it's an exhaust leak
that causes backfires is that that is where they see or hear the
backfire happening.  The fact is that it must be the case that it is
engine tuning that is the cause of any backfire.  Incorrect valve lash,
incorrect point gap, incorrect plug gap, incorrect timing, imporperly
jetted carbs, manifold leaks can all contribute to backfires (or any
combination thereof.)  It also stands to reason that it is real easy to
swap in a new exhaust system versus trying to tune ones car.  When one
calls any of the advertisers in the various VW magazines, they
undoubtedly say it's an exhaust leak which causes backfires and they
have an exhaust system that MIGHT cure it.  Check out the true cause(s)
of your engine ails and don't just start swapping parts.  

I think that part of this "Hobby" of ours is to become enlightended
about the workings and engineering of our cars.  They are designed a
certain way to be operated a certain way.  Ours is to understand what
that "WAY" is not just swap parts for the sake of being "cool".

I yield the floor.




----------
From: 	Steven Ayres[SMTP:comwest@well.com]
Sent: 	Tuesday, July 21, 1998 9:46 AM
To: 	type3@vwtype3.org
Subject: 	Re: Backfire


JimA=> the exhaust is under postiive pressure and will almost never draw

=> air INTO itself.  

These objections make a lot of sense to me, and the common explanation 
for exhaust pops has never satisfied me. I wonder what you (or anyone 
else here) think *does* cause this phenomenon. 

In fact, I wonder every time I leave my house in my Bus with the exhaust

leak. I live on a steep hill, so as soon as I leave the drive I'm 
engine-braking in first. The exhaust assembly isn't hot enough at that 
point to cause anything to detonate. It reliably gives me a rapid 
popping until I put on some load at the bottom of the hill. I don't like

it.

Steven Ayres, Prescott AZ