Offensive Tail Pipe smell

[wayne rogewski]

Thankfully no need for Beno or Gas X for me at this point. But in asking the family what one thing they would change on the Coach. Without
hesitation the CFO said "the Exhaust smell".

As it stands currently, Its a 403 with 120K miles. Stock Carb, stock distributor, good Manifolds, Lenzi copper gaskets, New mufflers, collector
donuts, no leaks.

The smell is not leaching into the coach per se. Its the eye burning and choking fumes when idling that is the offensive smell. So much that we
have to close all the windows in the house, neighbors too, and it sticks to my clothes instantly.

What I do know. The carb needs to be rebuilt. No question it lopes when starting up, has hesitations and I know its time. None of the PO paperwork
suggests that it was ever rebuilt. The distributor is in good shape, and working properly. Timing was set by a shop per the manual specs.

So my questions, Do you think a rebuilt carb (Patterson) would help clean up the eye burning smell? Understanding that there are no cats on this,
and no real emissions to speak of. Would it at least help?

In reading up recently on the FiTech set up from Mr. Work, I read that system helped clean up the smell just a bit. So thats a possibility on the
table.

I am by no means a carb guru and will gladly pay to have that properly redone the first time correctly. I know enough to not know if its an air/fuel
setting out of whack, or something else. So if it is a fuel delivery issue, would you have the carb rebuilt or go to EFI?

What say the masses on how I can make the CFO happy?
--
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies.
Mid Michigan

 

[Carl Stouffer]

It sounds to me like it is running rich, at idle. A carb rebuild and proper adjustment of the idle mixture screws and choke will definitely make a
big difference. New spark plugs, ignition wires and a check of the timing coulodn't hurt either.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.

 

[wayne rogewski]

Thanks Carl, I would add the plugs are Autolite 847s. Gapped to .60 and have about 600 miles on them. The wires are newer Bosch 8mm. The
distributor / timing was set about 600 miles ago as well.

--
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies.
Mid Michigan

 

[Jim Hupy]

Old gasoline?
Jim Hupy
Salem, Or
78 GMC ROYALE 403

> Thanks Carl, I would add the plugs are Autolite 847s. Gapped to .60 and
> have about 600 miles on them. The wires are newer Bosch 8mm. The
> distributor / timing was set about 600 miles ago as well.
>
> --
> 77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies.
> Mid Michigan
>
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[wayne rogewski]

The gas in it right now is about 2 months old. I have been running the generator a decent bit this winter and warming up the coach. Put 5 gallons of
fresh in last week to keep the tanks topped off.

I would say it was stinky this summer as well running almost 100 gallons of fresh fuel through it in a weeks time.


--
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies.
Mid Michigan

 

[Jim Hupy]

So that eliminates one possible cause. That narrows it down a bit. Check
the choke setting. When stone cold, the choke plate should be adjusted so
that it barely closes completely. Also, use a vacuum pump to verify the
choke pull off. It should hold vacuum with no leakdown. Make sure the hoses
are hooked up correctly.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

> The gas in it right now is about 2 months old. I have been running the
> generator a decent bit this winter and warming up the coach. Put 5 gallons
> of
> fresh in last week to keep the tanks topped off.
>
> I would say it was stinky this summer as well running almost 100 gallons
> of fresh fuel through it in a weeks time.
>
>
> --
> 77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies.
> Mid Michigan
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[john r. lebetski]

That really eye burn stuff is usually too lean. If no black smoke it may not be too rich. Any old school shop with an exhaust gas analyser should be
able to get a mixture reading.
--
John Lebetski
Woodstock, IL
77 Eleganza II
Source America First

 

[a.]

> It sounds to me like it is running rich, at idle. A carb rebuild and proper adjustment of the idle mixture screws and choke will definitely make
> a big difference. New spark plugs, ignition wires and a check of the timing coulodn't hurt either.
On a cold start, it is common for 70's tech chokes to refuse to budge as the engine warms up unless you are working the accelerator (driving). That
will richen the mixture as it warms up. You will notice the idle gets faster and faster when it does that. A quick stab on the accelerator will free
it up and idle it down. Should clear up the fumes too.

If that's not what is happening, adjust the idle mixture for some immediate relief, then do a carb rebuild at your leisure.
--
'73 23' Sequoia For Sale
'73 23' CanyonLands Parts Unit For Sale
Upper Alabama
Why don't they sell spray paint that washes off with soap and water for graffiti vandals to use?

 

[Larry Davick]

My wife has some kind of bionic sense of smell and we chased the smells quite a lot. At first it was raw fuel - replaced all the hoses. The raw few smell returned after parking - fuel boiling out of the carb on the 455 because of the exhaust crossover. Installed the Howell manifold. Poor performance and sooty exhaust - stinking in the coach - replaced exhaust manifold gases with Reflex, tried to adjust the carburetor. Too lean - different stink from the exhaust - had cheap muffler and pipes installed, adjusted carburetor. Finally pulled the trigger and installed Howell EFI and an electronic distributor, the timing chain is about 75k miles old. She purrs like a kitten at idle. Really - it’s beautiful to listen to the exhaust burble.

I’m not saying you have to go that far! Still, keep the timing chain, distributor advance mechanisms, and of course the carburetor in mind as suspects.

Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, CA
Howell EFI + EBL + Electronic Distributor

 

[dan borlase]

Is it possable that your coach is suffering from "chipmonk cheeks" also known as bulging at the beltline at the cock pit area. The result is a
significant gapping at the floor where the floor meets the side walls by the driver and passenger seats. This allows a large amount of "noxious
gasses" to enter the coach when stoped and idleing.
The accepted fix is to get into the wheel wells where when looking up you see this gap...fill this gap with expanding insulating foam (be sure to get
the limited expanding formula as opposed to the extended expand type). This should seal the opening and eliminate the migration of noxious oders from
entering the cock pit easely.

 

[wayne rogewski]

Appreciate the responses and thoughts. The smell is not leaching into the cabin (Fixed that with new mufflers and donuts at the manifolds. Its more
everything around it outside which is gassed out. I will take a look at the choke and all the vacuum hoses. I know at minimum the choke is working
some as I can kick it down once it warms up a bit. Its still the mechanical choke with the stove pipe, and is nearly fully closed when its cold out.
Once warm it does idle nicely around 900 rpm.

At minimum I know the carb should be rebuilt. From the sounds of it this may help fix some of the issues. If not I will go to EFI and have a
freshly rebuilt carb as a back up or to sell.

--
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies.
Mid Michigan