re: new scout 800 owner

[David Nedved <david_nedved@domain.elided>]

>Date: Mon, 5 Apr 1999 20:26:55 -0400 (Eastern Daylight Time)
>From: wisser@domain.elided (Bill Wisser)
>Subject: new scout 800 owner
>
>one has a gaping hole.  Now, there is a loud popping on deceleration in
>gear.  Supposedly the carb has been recently rebuilt, though I have yet
>to go through and do a thorough tune-up.  My question is, is the
>popping
>caused by the compromised glasspacks, or is this backfiring due to
>misadjusted timing (or whatever) which may have caused the muffler to
>have a hole in the first place?  I ask because I am planning to get the
>mufflers changed out soon, and do not want to risk blowing another
>muffler before I get the chance to do a good tune-up.

Bill,

My 78 Scout II 345 with glasspacks does this.  It didn't do it as
badly before I put the glasspacks on (running "car mufflers"), but did
it much worse when I drove it around with missing exhaust donuts!  I
think it's basically gentle backfiring caused by loss of compression
through the exhaust valves, made worse by lowered backpressure.  As
far as I know any old engine will do the same thing.  You can't
downshift in an old IHC the same way you can in a little Japanese
5-speed!  When you do the compression braking it seems to sorta' force
burning gas out the exhaust valves... probably not an accurate
description of the event, but that's how I think of it in my mind.

I know that my engine probably doesn't have the hardened valve seats,
and I certainly don't run leaded gas, so I expect to have the problem
until (unless?) I do a valve job.  And if I do a valve job, I'll
probably need a ring job, so might as well go ahead and do it.  And
I've always heard not to tighten up the upper end without rebuilding
the lower end... you get the picture... it doesn't run badly enough to
justify an entire rebuild.

BTW, you mentioned blowing mufflers.  I ended up blowing up my "car
mufflers" about 3 months after switching from automatic to manual
transmission.  I switched to cherry bombs because the owner of the
local Midas said he would personally replace them if I managed to blow
one up, plus they were cheaper.  I like the way the glasspacks sound,
so I personally would think twice about switching from glasspacks back
to normal mufflers.  You might have even more problems with normal
mufflers exploding... I certainly did.  (And it'll scare the crap out
of you when it does it too - especially if it's in the morning on the
way to work and you're half-asleep!)

About the tune-up, go ahead and do it anyway, but I wouldn't expect
that adjusting the timing, mix, new plugs, wires, cap, rotor,
(whatever you mean by a tuneup) would affect this too much, but I'm
frequently wrong!
If you do and it makes a big difference, be sure to let me know.

Keep in mind it's $0.02 worth from an untrained non-mechanic...

David
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