Re: [T3] Backfiring...

[Jim Adney <jadney@vwtype3.org>]

On 9 Oct 2003 at 15:20, William Kunz wrote:

> Can someone give me an overview about why an engine
> would backfire? My particular instances have been when
> the car is first started. I have a 69 SQBK dual carb
> (FI conversion). What might I start to look at? Also,
> how dangerous is it?

True backfires (where you get a blast backwards thru the carb) are rare. You 
probably are getting something I don't know a better name for, which is an 
explosion in the exhaust system. The cause is the accumulation of unburned fuel 
in the exhaust, which is then ignited by the hot gasses when the exhaust valve 
opens. You might want to experiment with different starting techniques, to see 
if you can come up with one which gets the engine started faster, with less 
unburned gas passed to the exhaust. Likewise, it might also be worthwhile to 
check the adjustment of your choke, if you have one.

It's not at all dangerous to you, but it can destroy a muffler, if that muffler 
has already been weakened by rust.

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

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org