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Date: Mon, 3 May 2010 12:02:02 -0400
Message-ID: <q2s1ab24f411005030902yd94e69et1c5edd457187b898@mail.gmail.com>
Subject: Backfire.
From: Lynn Hanover <lehanover@gmail.com>
To: flyrotary@lancaironline.net
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kevin lane wrote:
> my new engine has been hard to start.  the other weekend I experienced
> a big bang [backfire I guessed].  today I noticed my intake manifold
> has a bit of a leak!  my design assumption that it would always be in
> a slight vacuum state was obviously wrong.  need to check the carb I
> guess to see if anything happened to it.
>
>
>
Kevin, is that just an aluminum shoebox, bolted to a plate and then
sealed with blue-goo?  Seems like it would be really simple
construction, and the side blowing out would help to protect the carb in
the case of a backfire.


The Weber is not affected by a backfire. This can also happen with injected
engines. You must assume this will happen, and note that modern intake log
manifolds are overly robust and the throttle bodies have thicker than needed
butterflies. So when this occurs the butterfly does not fold around the
throttle shaft, or stick closed from a bent butterfly or shaft.

Even the Renesis, with no overlap at all can do this. More likely a glowing
carbon grain lighting off the mixture with the intake port still open. Could
also be too high a heat range spark plugs.  Not a timing problem if the
engine is running.

Mothers 58 Olds did this for many minutes after shut down. It "ran on" as it
was called back then. In the age before converters, you could slowly pour in
a Coke bottle full of water into each side of the giant 4 barrel to flush
away the carbon. Works on rotaries as well.
Ruins converters. Just pour the water slowly enough that the engine does not
stumble at 2,000 RPM. Done just before a rebuild, the engine will be carbon
free.
You could rev up the engine, shut off the ignition, and go to full throttle
to chill the carbon. Worked most of the time.
The engine would die with no drama.

You must plan for this in design. The inlet right through the air cleaner
should be looked at as a pressure vessel. My air cleaner cover is held on
with springs. The over pressure cycles the springs and all returns to
normal.

Lynn E. Hanover
--
Homepage:  http://www.flyrotary.com/
Archive and UnSub:
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<div>kevin lane wrote:<br>&gt; my new engine has been hard to start.=A0 the=
 other weekend I experienced <br>&gt; a big bang [backfire I guessed].=A0 t=
oday I noticed my intake manifold <br>&gt; has a bit of a leak!=A0 my desig=
n assumption that it would always be in <br>
&gt; a slight vacuum state was obviously wrong.=A0 need to check the carb I=
 <br>&gt; guess to see if anything happened to it.<br>&gt;=A0 <br>&gt;=A0 <=
br>&gt;<br>Kevin, is that just an aluminum shoebox, bolted to a plate and t=
hen <br>
sealed with blue-goo?=A0 Seems like it would be really simple <br>construct=
ion, and the side blowing out would help to protect the carb in <br>the cas=
e of a backfire.<br>=A0</div>
<div>=A0</div>
<div>The Weber is not affected by a backfire. This can also happen with inj=
ected engines. You must assume this will happen, and note that modern intak=
e log manifolds are overly robust and the throttle bodies have thicker than=
 needed butterflies. So when this occurs the butterfly does not fold around=
 the throttle shaft, or stick closed from a bent butterfly or shaft. </div>

<div>=A0</div>
<div>Even the Renesis, with no overlap at all can do this. More likely a gl=
owing carbon grain lighting off the mixture with the intake port still open=
. Could also be too high a heat range spark plugs.=A0 Not a timing problem =
if the engine is running.</div>

<div>=A0</div>
<div>Mothers 58 Olds did this for many minutes after shut down. It &quot;ra=
n on&quot; as it was called back then. In the age before converters, you co=
uld slowly pour in a Coke bottle full of water into each side of the giant =
4 barrel to flush away the carbon. Works on rotaries as well. </div>

<div>Ruins converters. Just pour the water slowly enough that the engine do=
es not stumble at 2,000 RPM. Done just before a rebuild, the engine will be=
 carbon free.</div>
<div>You could rev up the engine, shut off the ignition, and go to full thr=
ottle to chill the carbon. Worked most of the time.</div>
<div>The engine would die with no drama.</div>
<div>=A0</div>
<div>You must plan for this in design. The inlet right through the air clea=
ner should be looked at as a pressure vessel. My air cleaner cover is held =
on with springs. The over pressure cycles the springs and all returns to no=
rmal. </div>

<div>=A0</div>
<div>Lynn E. Hanover<br>--<br>Homepage:=A0 <a onclick=3D"return top.js.Open=
ExtLink(window,event,this)" href=3D"http://www.flyrotary.com/" target=3D"_b=
lank">http://www.flyrotary.com/</a><br>Archive and UnSub:=A0=A0 <a onclick=
=3D"return top.js.OpenExtLink(window,event,this)" href=3D"http://mail.lanca=
ironline.net:81/lists/flyrotary/List.html" target=3D"_blank">http://mail.la=
ncaironline.net:81/lists/flyrotary/List.html</a><br>
=A0</div>

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