[ihc] Re: Scout warm-up issues

["Tom Anderson" <ande1054@xxxxxxxxxxxx>]

Ryan wrote:

>>> This last week I paid particular attention to the scout's warm up to see
>>> exactly what it does when it gets to it's trouble spot.

>>> It always starts great and it'll run perfectly regardless of temp, I'd
>>> venture to guess I could kick off the choke immediately too and it'd be
>> fine
>>> at first.

>>> Here's what happens...

>>> It'll start great and be running along fine.  let it idle to warm up.
>> It's
>>> running fine.  Then the rpm drops a little. Takes a while before it starts
>>> dropping but once it does it's fairly quick.  A slow and steady decline in
>>> rpm until it bottoms out at around 400 or 500 rpm sounding like it's only
>>> hitting on a few cylinders (I need to get a tach so I can verify the
>> rpms).

My '77 Scout does the same thing when the ambient temp is around 30
to 40 F, and the humidity is high. I suspect that you have
conditions similar to that most of the winter. You are in GA,
right? The carb is icing up. The ice chokes the air off, causing a
rich mixture. Does the exhaust smell bad when the problem occurs?
Does it blow black smoke? Those two symptoms indicate an excessively
rich mixture. If you look down the carb, when the problem is
ocurring, you may be able to see the ice in the venturis.

>>> It'll stay that way for a while, can't touch anything becuase kicking off
>>> the fast idle will cause it to just die.  It'll do that for a few minutes
>>> and then out of nowhere the idle will bump up a notch, not a whole lot,
>> just
>>> 50 rpms or so, it's a sudden surge.  After that though it starts the same
>>> progression as initially except in reverse until it's at normal fast idle.

The carb is getting warm enough to start melting the ice.

>>> Then I can kick the fast idle off and go.   I can drive before then but I
>>> have to be careful to keep some pedal in or it'll die (doesn't bother me
>> too
>>> much, I like to let the scout warm up before driving anyway).  It does
>> kind
>>> of bother me though the way it does that.

>>> It runs really bad during that period.  Sitting there barely hitting,
>> whole
>>> scout shuddering and rocking a little as the engine hits along.  It's
>> going
>>> slow enough that I want to say I could easily count the number of loops my
>>> alternator belt does while it's doing that (yeah a tach would really help
>> on
>>> getting that RPM, I'm kind of curious how fast it's going).

>>> It's a pretty drastic difference.  Takes about 30 seconds I'd say to go
>> from
>>> initial great running to bad and another 30 seconds to get good again
>> after
>>> a few minutes of barely puttering along.  Also, it only does it when it's
>>> cold.

>>> I've tried to mess with the choke some while it's doing that with no
>>> effect... any suggestions on what I should look at?

Your heat riser valve. Mine is not functional. The spring is
broken, so the valve stays open all the time. When the engine is
cold, the counter weight on the valve should be up. The spring
should hold it there. When you push the weight down, it should
spring back up, when released. When the engine warms up, the
bimetal spring relaxes, and the weight opens the valve.

>>> New ignition module and coil and it did it with the old ones too (which
>> are
>>> now my spares).  Prestolite electronic ign and the infamous stock holley
>>> 2bbl carb...

>> My 4bbl Edelbrock (weber, carter),  with the electric choke does the same.
>> My engine is a 392 IC.  I have felt that it is a problem with the ratio of
>> enriching as it needs less and less in the warming process.  I am eager to
>> hear from the experience of others.  Jim A.

>>> It's been doing it for a long time, but it's one of those things that kind
>>> of annoys me.... ok, it greatly annoys me, but I have no idea how to
>>> troubleshoot this one.  I don't remember seeing anything about this type
>> of
>>> problem in the troubleshooting section of the service manual.

>>> Thanks,
>>> Ryan

> ------------------------------

> Yes it has a heat riser.  It moves freely.  I'm assuming it's working
> properly?

Just because the valve moves freely, doesn't mean it's working. The
valve should spring to the closed position (counter weight up),
when the engine is cold.

> Exhaust still comes out both sides, but there does seem to be a slight
> difference in pressure when warming up.

> - -Ryan

Tom Anderson
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