Re: Help, scout

[jlandry@domain.elided (John A. Landry)]

In a brilliant stroke of genius, cookiedan@domain.elided (Daniel Nees) blurted
out:

>DBond@domain.elided (David Bond) Date: Tue, Dec 15, 1998, 1:52pm  
>Hey Dan, 
>Could you post a message on IHC-digest for me? OR, if you know what is
>wrong, just tell me! I have a 78 Scout II with a 4 popper in it. When
>the engine is warm and I shut it down, it makes on hell-of-a backfire!
>Makes all the people jump and dive for cover! I've played with the
>timing, retarding and advancing and nothing seems to help! I have
>dieseling too, but I credit that to poor gas! It runs just fantastic,
>just can't get rid of the explosion when I shut her down! 

David,

Sadly, when an engine is doing this it usually means you have combination
of problems traceable to neglect or lack of maintenance.  The backfiring at
shut down is undoubtedly related to the dieseling problem.

When an engine diesels, it's usually caused by a combination of the
throttle not being closed *enough* at shutdown and / or an overly rich air
/ fuel mixture.  The engine is simply receiving enough fuel and air so that
any slight ignition source will keep it running.  A hot engine with glowing
deposits in the combustion chamber are all you need for ignition.
Excessive timing advance aggravates the situation just prior to shutdown by
causing high combustion chamber temps.

In rare cases, sometimes vehicle wiring (and alternator) problems can cause
enough feedback into the ignition system to where you're not shutting off
the ignition.  Aftermarket self contained ignition system are especially
susceptible to this.

As to the backfiring after shutdown, my guess is this...

Your carb could be set way too rich (either because it's in need of a
rebuild or it's simply set wrong) which loads up the cylinders and exhaust
system with lots of unburned fuel.  The engine diesels and doesn't do a
good job burning all the fuel it's pumping through, so this fuel loading
gets excessive.  When the engine finally does stop dieseling, the heat from
the combustion chamber and exhaust system causes this fuel to auto-ignite
and you get the loud bang!  This is the same thing as shutting off the
ignition when coasting and then turning it back on... it can blow a rotten
muffler completely off a vehicle.

What to do?

First, look at your spark plugs and exhaust tail pipe.  Are they black and
sooted?  Then you definitely have an over rich air fuel mixture!  Start
with the basics!  Rebuild your carb and give your engine a good tune-up and
inspection!  If you don't know how to do this, then have it professionally
done or get training.  The engine needs to be in good tune first and then
the carb can be properly adjusted.  Don't neglect the choke settings...
they are often implicated in dieseling problems.  Check that the
distributor is working properly and set the timing correctly.

Good luck,

John L.
-------------------------------------------------------------------------- 
jlandry AT halcyon DOT com      |
Conservative Libertarian        |  Scout(R) the America others pass by
Life Member of the NRA          | in the Scout Traveler escape-machine.
WA Arms Collectors              |
Commercial Helicopter - Inst.   | 1976 Scout II Traveler "Patriot" model
http://www.halcyon.com/jlandry/ |     1977 Scout II Traveler (Parts)