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Exhaust bang bang bang

JH
James Hupy
Wed, Sep 15, 2021 2:13 PM

Matt, it takes many years of setting "lean drop" to do it without a tach
and vacuum gage. (TacVac).
It requires a fully warmed- up engine, and 8 cylinders that are within
10% compression pressure of each other, really tuned to factory ignition
specs, good wires, plugs, rotor, cap, etc.
In other words, a textbook perfect engine. If anything has been
monkeyed with, like pcv, or vacuum advance, or air cleaner, etc. Then all
bets are off.
Then, the best a person can hope for is a low CO reading at the
tailpipe, and a somewhat steady state idle at 650 rpm + or - 100 rpm either
way.
I try to set idle speed so that no dieseling or "running on" happens
on a hot engine when the ignition is switched off with the transmission in
neutral, and the A/C system off as well.
Real world stuff applies here, most of these GMC'S are high mileage
with leaky headers, etc., etc. Makes idle tuning a challenge for sure.
Then you take in humidity, altitude, barometric pressure, etc.
Challenge for sure.
Jim Hupy
Salem, Oregon

On Wed, Sep 15, 2021, 6:49 AM Matt Colie matt7323tze@gmail.com wrote:

boybach wrote on Tue, 14 September 2021 20:18

JohnL455 wrote on Tue, 14 September 2021 13:27

Mine will “burble” during long engine braking, but I have my exact  GM

copy exhaust system installed so it is barely noticeable.

I suspect your idle mixture may be adding extra fuel causing this to

be more pronounced.  If you have 3” stainless this may exaggerate it.

Correct mixture is balanced best idle just at the lean drop edge.

“Emissions” setting would be 25 RPM lean drop per side to get 50 RPM lean

drop.

I have no way to check or test emissions, should I adjust the

carburetor? How do I do that?

BTW, I have no idea what this statement means  :d "Correct mixture is

balanced best idle just at the lean drop edge."

Larry

While John's description is good, it does not make two points.

There are two idle screws in the carburetor base that must be balanced.  I
find the "around the corner" special screw driver and a mirror to be
essential.

The lean drop edge is when the mixture is lean and if it goes any leaner
at all, there is a precipitous drop in the idle speed.  Without a tachometer
and possibly a vacuum gauge, I don't know how one finds this.  I did know
one man that could, but he passed years back.

Matt

Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL,
GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum
Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit


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Matt, it takes many years of setting "lean drop" to do it without a tach and vacuum gage. (TacVac). It requires a fully warmed- up engine, and 8 cylinders that are within 10% compression pressure of each other, really tuned to factory ignition specs, good wires, plugs, rotor, cap, etc. In other words, a textbook perfect engine. If anything has been monkeyed with, like pcv, or vacuum advance, or air cleaner, etc. Then all bets are off. Then, the best a person can hope for is a low CO reading at the tailpipe, and a somewhat steady state idle at 650 rpm + or - 100 rpm either way. I try to set idle speed so that no dieseling or "running on" happens on a hot engine when the ignition is switched off with the transmission in neutral, and the A/C system off as well. Real world stuff applies here, most of these GMC'S are high mileage with leaky headers, etc., etc. Makes idle tuning a challenge for sure. Then you take in humidity, altitude, barometric pressure, etc. Challenge for sure. Jim Hupy Salem, Oregon On Wed, Sep 15, 2021, 6:49 AM Matt Colie <matt7323tze@gmail.com> wrote: > boybach wrote on Tue, 14 September 2021 20:18 > > JohnL455 wrote on Tue, 14 September 2021 13:27 > > > Mine will “burble” during long engine braking, but I have my exact GM > copy exhaust system installed so it is barely noticeable. > > > I suspect your idle mixture may be adding extra fuel causing this to > be more pronounced. If you have 3” stainless this may exaggerate it. > > > Correct mixture is balanced best idle just at the lean drop edge. > “Emissions” setting would be 25 RPM lean drop per side to get 50 RPM lean > > > drop. > > > > I have no way to check or test emissions, should I adjust the > carburetor? How do I do that? > > > > BTW, I have no idea what this statement means :d "Correct mixture is > balanced best idle just at the lean drop edge." > > > > > > Larry > > While John's description is good, it does not make two points. > > There are two idle screws in the carburetor base that must be balanced. I > find the "around the corner" special screw driver and a mirror to be > essential. > > The lean drop edge is when the mixture is lean and if it goes any leaner > at all, there is a precipitous drop in the idle speed. Without a tachometer > and possibly a vacuum gauge, I don't know how one finds this. I did know > one man that could, but he passed years back. > > Matt > -- > Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, > GMCES > Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum > Brakes with Applied Control Arms > SE Michigan - Near DTW - Twixt A2 and Detroit > _______________________________________________ > GMCnet mailing list > Unsubscribe or Change List Options: >
T
twlldeen@gmail.com
Wed, Sep 15, 2021 4:20 PM

Well after reading the above I am both encouraged and discouraged! My coach isn't really very high mileage at all, but it is, like the others, old -
so maybe things have decomposed. I don't know. In the last 10 or 12 years it was only driven on three trips until I started camping this year.

Trip one was from Bakersfield, California to BC then across Canada to Belleville Ontario. Long haul. Second was from Belleville Ontario to Scotch
Creek BC. In the interim the coach spent 10 years indoors at a Belleville school bus fleet heated garage. Trip 3 was the delivery journey I made in
March of this year, Scotch Creek to Victoria BC. Those trips added about 8500 miles and the odometer just turned 40,000 when I got the coach to the
island.

Engine idles and runs smoothly, roars up hills with no problem and doesn't diesel on shutdown. If I were to describe the engine's behavior, I'd have
to say she "runs like a top".

So ...do I start messing with things or just leave it be and put up with the popping exhaust on steep downgrades? :?

Larry

Larry - Victoria BC -

1977 Palm Beach 40,000 miles, PO said everything working but forgot the word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system,
6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses

Well after reading the above I am both encouraged and discouraged! My coach isn't really very high mileage at all, but it is, like the others, old - so maybe things have decomposed. I don't know. In the last 10 or 12 years it was only driven on three trips until I started camping this year. Trip one was from Bakersfield, California to BC then across Canada to Belleville Ontario. Long haul. Second was from Belleville Ontario to Scotch Creek BC. In the interim the coach spent 10 years indoors at a Belleville school bus fleet heated garage. Trip 3 was the delivery journey I made in March of this year, Scotch Creek to Victoria BC. Those trips added about 8500 miles and the odometer just turned 40,000 when I got the coach to the island. Engine idles and runs smoothly, roars up hills with no problem and doesn't diesel on shutdown. If I were to describe the engine's behavior, I'd have to say she "runs like a top". So ...do I start messing with things or just leave it be and put up with the popping exhaust on steep downgrades? :? Larry -- Larry - Victoria BC - 1977 Palm Beach 40,000 miles, PO said everything working but forgot the word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system, 6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses
TS
Todd Sullivan
Wed, Sep 15, 2021 4:32 PM

Have you tried switching fuels?

Sully
Bellevue wa

On Wed, Sep 15, 2021 at 9:20 AM twlldeen@gmail.com wrote:

Well after reading the above I am both encouraged and discouraged! My
coach isn't really very high mileage at all, but it is, like the others,
old -
so maybe things have decomposed. I don't know. In the last 10 or 12 years
it was only driven on three trips until I started camping this year.

Trip one was from Bakersfield, California to BC then across Canada to
Belleville Ontario. Long haul. Second was from Belleville Ontario to Scotch
Creek BC. In the interim the coach spent 10 years indoors at a Belleville
school bus fleet heated garage. Trip 3 was the delivery journey I made in
March of this year, Scotch Creek to Victoria BC. Those trips added about
8500 miles and the odometer just turned 40,000 when I got the coach to the
island.

Engine idles and runs smoothly, roars up hills with no problem and doesn't
diesel on shutdown. If I were to describe the engine's behavior, I'd have
to say she "runs like a top".

So ...do I start messing with things or just leave it be and put up with
the popping exhaust on steep downgrades? :?

Larry

Larry - Victoria BC -

1977 Palm Beach 40,000 miles, PO said everything working but forgot the
word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system,
6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses


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Have you tried switching fuels? Sully Bellevue wa On Wed, Sep 15, 2021 at 9:20 AM <twlldeen@gmail.com> wrote: > Well after reading the above I am both encouraged and discouraged! My > coach isn't really very high mileage at all, but it is, like the others, > old - > so maybe things have decomposed. I don't know. In the last 10 or 12 years > it was only driven on three trips until I started camping this year. > > Trip one was from Bakersfield, California to BC then across Canada to > Belleville Ontario. Long haul. Second was from Belleville Ontario to Scotch > Creek BC. In the interim the coach spent 10 years indoors at a Belleville > school bus fleet heated garage. Trip 3 was the delivery journey I made in > March of this year, Scotch Creek to Victoria BC. Those trips added about > 8500 miles and the odometer just turned 40,000 when I got the coach to the > island. > > Engine idles and runs smoothly, roars up hills with no problem and doesn't > diesel on shutdown. If I were to describe the engine's behavior, I'd have > to say she "runs like a top". > > So ...do I start messing with things or just leave it be and put up with > the popping exhaust on steep downgrades? :? > > Larry > -- > Larry - Victoria BC - > > 1977 Palm Beach 40,000 miles, PO said everything working but forgot the > word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system, > 6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses > _______________________________________________ > GMCnet mailing list > Unsubscribe or Change List Options: >
T
twlldeen@gmail.com
Wed, Sep 15, 2021 5:35 PM

sgltrac wrote on Wed, 15 September 2021 09:32

Have you tried switching fuels?

Sully
Bellevue wa

No, I just run regular ...are you suggesting running higher octane? I know higher octane has less oomph than regular but I don't ping or diesel ATM
...there isn't much difference in brands up here AFAIK, so hate to throw another tankful or two in her at 20ȼ a litre (about 50ȼ a US gallon) for
"premium"  8o

Larry

Larry - Victoria BC -

1977 Palm Beach 40,000 miles, PO said everything working but forgot the word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system,
6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses

sgltrac wrote on Wed, 15 September 2021 09:32 > Have you tried switching fuels? > > Sully > Bellevue wa No, I just run regular ...are you suggesting running higher octane? I know higher octane has less oomph than regular but I don't ping or diesel ATM ...there isn't much difference in brands up here AFAIK, so hate to throw another tankful or two in her at 20ȼ a litre (about 50ȼ a US gallon) for "premium" 8o Larry -- Larry - Victoria BC - 1977 Palm Beach 40,000 miles, PO said everything working but forgot the word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system, 6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses
MH
Mike Hamm
Wed, Sep 15, 2021 8:17 PM

Try filling from half full with premium gas.
I usually alternate premium to regular when filling from about half full.
Seems to run better that regular only.

1977 Kingsley 455 as stock as it gets except lots of Ragusa parts

Try filling from half full with premium gas. I usually alternate premium to regular when filling from about half full. Seems to run better that regular only. -- 1977 Kingsley 455 as stock as it gets except lots of Ragusa parts
JR
John R. Lebetski
Wed, Sep 15, 2021 8:56 PM

Matt I think I went into detail to state to use a tach and how and why both mixture screws must both be adjusted. If you have a good ear (retired
audio eng) you can do it by pitch as that correlates to a finite RPM.  When trimming for the absolute edge, eyes and ears are best together.
Larry. Start by just checking base idle speed.  A 50 RPM difference could minimize your issue.

John Lebetski
Woodstock, IL
77 Eleganza II

Matt I think I went into detail to state to use a tach and how and why both mixture screws must both be adjusted. If you have a good ear (retired audio eng) you can do it by pitch as that correlates to a finite RPM. When trimming for the absolute edge, eyes and ears are best together. Larry. Start by just checking base idle speed. A 50 RPM difference could minimize your issue. -- John Lebetski Woodstock, IL 77 Eleganza II
TS
Todd Sullivan
Wed, Sep 15, 2021 9:08 PM

I mean non ethanol vs ethanol.

Sully
Bellevue wa

On Wed, Sep 15, 2021 at 10:35 AM twlldeen@gmail.com wrote:

sgltrac wrote on Wed, 15 September 2021 09:32

Have you tried switching fuels?

Sully
Bellevue wa

No, I just run regular ...are you suggesting running higher octane? I know
higher octane has less oomph than regular but I don't ping or diesel ATM
...there isn't much difference in brands up here AFAIK, so hate to throw
another tankful or two in her at 20ȼ a litre (about 50ȼ a US gallon) for
"premium"  8o

Larry

Larry - Victoria BC -

1977 Palm Beach 40,000 miles, PO said everything working but forgot the
word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system,
6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses


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I mean non ethanol vs ethanol. Sully Bellevue wa On Wed, Sep 15, 2021 at 10:35 AM <twlldeen@gmail.com> wrote: > sgltrac wrote on Wed, 15 September 2021 09:32 > > Have you tried switching fuels? > > > > Sully > > Bellevue wa > > No, I just run regular ...are you suggesting running higher octane? I know > higher octane has less oomph than regular but I don't ping or diesel ATM > ...there isn't much difference in brands up here AFAIK, so hate to throw > another tankful or two in her at 20ȼ a litre (about 50ȼ a US gallon) for > "premium" 8o > > Larry > -- > Larry - Victoria BC - > > 1977 Palm Beach 40,000 miles, PO said everything working but forgot the > word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system, > 6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses > _______________________________________________ > GMCnet mailing list > Unsubscribe or Change List Options: >
T
twlldeen@gmail.com
Wed, Sep 15, 2021 10:03 PM

JohnL455 wrote on Wed, 15 September 2021 13:56

Matt I think I went into detail to state to use a tach and how and why both mixture screws must both be adjusted. If you have a good ear (retired
audio eng) you can do it by pitch as that correlates to a finite RPM.  When trimming for the absolute edge, eyes and ears are best together.
Larry. Start by just checking base idle speed.  A 50 RPM difference could minimize your issue. That’s the throttle stop screw on accelerator
linkage drivers side of Qjet.

Thanks John, I hear you  :lol:

Larry

Larry - Victoria BC -

1977 Palm Beach 40,000 miles, PO said everything working but forgot the word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system,
6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses

JohnL455 wrote on Wed, 15 September 2021 13:56 > Matt I think I went into detail to state to use a tach and how and why both mixture screws must both be adjusted. If you have a good ear (retired > audio eng) you can do it by pitch as that correlates to a finite RPM. When trimming for the absolute edge, eyes and ears are best together. > Larry. Start by just checking base idle speed. A 50 RPM difference could minimize your issue. That’s the throttle stop screw on accelerator > linkage drivers side of Qjet. Thanks John, I hear you :lol: Larry -- Larry - Victoria BC - 1977 Palm Beach 40,000 miles, PO said everything working but forgot the word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system, 6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses
T
twlldeen@gmail.com
Wed, Sep 15, 2021 10:07 PM

sgltrac wrote on Wed, 15 September 2021 14:08

I mean non ethanol vs ethanol.

Sully
Bellevue wa

We don't have much of a choice in that dept., I think only the top Chevron grade is ethanol free and that's some expensive stuff.

Thanks for the tip though

Larry

Larry - Victoria BC -

1977 Palm Beach 40,000 miles, PO said everything working but forgot the word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system,
6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses

sgltrac wrote on Wed, 15 September 2021 14:08 > I mean non ethanol vs ethanol. > > Sully > Bellevue wa We don't have much of a choice in that dept., I think only the top Chevron grade is ethanol free and that's some expensive stuff. Thanks for the tip though Larry -- Larry - Victoria BC - 1977 Palm Beach 40,000 miles, PO said everything working but forgot the word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system, 6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses
R
Rob
Wed, Sep 15, 2021 10:13 PM

If you want to try it - there are a few other choices locally that are supposed to be ethanol free:

Chevron 94
CO-OP premium
Costco Premium
Shell V-Power 91

https://www.pure-gas.org/index.jsp?stateprov=BC

Rob
76 Royale Twin Beds, Dry Bath
Victoria, BC

On Sep 15, 2021, at 3:07 PM, twlldeen@gmail.com twlldeen@gmail.com wrote:

sgltrac wrote on Wed, 15 September 2021 14:08

I mean non ethanol vs ethanol.

Sully
Bellevue wa

We don't have much of a choice in that dept., I think only the top Chevron grade is ethanol free and that's some expensive stuff.

Thanks for the tip though

Larry

Larry - Victoria BC -

1977 Palm Beach 40,000 miles, PO said everything working but forgot the word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system,
6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses

If you *want* to try it - there are a few other choices locally that are supposed to be ethanol free: Chevron 94 CO-OP premium Costco Premium Shell V-Power 91 https://www.pure-gas.org/index.jsp?stateprov=BC Rob 76 Royale Twin Beds, Dry Bath Victoria, BC > On Sep 15, 2021, at 3:07 PM, <twlldeen@gmail.com> <twlldeen@gmail.com> wrote: > > sgltrac wrote on Wed, 15 September 2021 14:08 >> I mean non ethanol vs ethanol. >> >> Sully >> Bellevue wa > > We don't have much of a choice in that dept., I think only the top Chevron grade is ethanol free and that's some expensive stuff. > > Thanks for the tip though > > > Larry > -- > Larry - Victoria BC - > > 1977 Palm Beach 40,000 miles, PO said everything working but forgot the word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system, > 6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses