Twisted fuel filter?

[6cuda61]

Anyone ever come across a twisted fuel filter in their carb? The filter i removed from my carb during rebuild had the end twisted and skewed sideways
a bit [which was possibly the cause of my off idle bog/amost stall]... after my rebuild or refresh the carb is lean [no noticeable vacuum leaks by
normal tests and appears to be running out of fuel in the mid throttle position. I haven't verified yet but i would bet a beer the filter is twisted
again and its preventing full fuel flow from entering the carb under low pump RPM.

Also their has been talk on the Vette forums about a sintered bronze filter instead....anyone know of such a beast for the motorhome?
--
Rich Mondor,

Brockville, ON

77 Hughes 2600

 

[joe ricke]

Have noticed twisted filter. Attributed it to installation (figured available surface area really didn’t change muck)..
What is your fuel pump situation? Added electric pump?
--
Joe Ricke - KE0CPM
Arden Hills, MN
'77 Transmode

 

[charles boyd]

Sir, is your filter pointing forward toward radiator or sideways toward valve cover? You may be using wrong filter.there should be room for a filter
and a spring.

> Anyone ever come across a twisted fuel filter in their carb? The filter i removed from my carb during rebuild had the end twisted and skewed
> sideways a bit [which was possibly the cause of my off idle bog/amost stall]... after my rebuild or refresh the carb is lean [no noticeable vacuum
> leaks by normal tests and appears to be running out of fuel in the mid throttle position. I haven't verified yet but i would bet a beer the filter
> is twisted again and its preventing full fuel flow from entering the carb under low pump RPM.
>
> Also their has been talk on the Vette forums about a sintered bronze filter instead....anyone know of such a beast for the motorhome?

--
C. Boyd
76 Crestmont
East Tennessee

 

[Bob Dunahugh]

GM called for a 2-micron filters in the carb. Yes. GM did have a bronze filter. But I have serious droughts that it's also 2 micron. The Q jet must have that 2-micron filter. Most in line filters are 20 micron. Some owners take the Q jet filter out. And think an in line filter will do the job. NO. It will not. But it will give you carb problems.
As to the twist. Most of those paper carb filters. Used a water base adhesive. Every time that I've found the filter coming apart like you're talking about. I found water in the tank. Something to think about.
Bob Dunahugh
78 Royale since 2003.
4 real COPO Yenkos

 

[6cuda61]

I don't have any experience with the coaches like you guys do but i didnt see any evidence of water in the float bowl/fuel when i took the carb
apart.

> GM called for a 2-micron filters in the carb. Yes. GM did have a bronze filter. But I have serious droughts that it's also 2 micron. The Q jet
> must have that 2-micron filter. Most in line filters are 20 micron. Some owners take the Q jet filter out. And think an in line filter will do the
> job. NO. It will not. But it will give you carb problems.
> As to the twist. Most of those paper carb filters. Used a water base adhesive. Every time that I've found the filter coming apart like you're
> talking about. I found water in the tank. Something to think about.
> Bob Dunahugh
> 78 Royale since 2003.
> 4 real COPO Yenkos
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

--
Rich Mondor,

Brockville, ON

77 Hughes 2600

 

[6cuda61]

All stock...

> Have noticed twisted filter. Attributed it to installation (figured available surface area really didn’t change muck)..
> What is your fuel pump situation? Added electric pump?

--
Rich Mondor,

Brockville, ON

77 Hughes 2600

 

[6cuda61]

It is the one that points forward and yes spring/gasket/install are all correctly done. Filter is the direct NAPA part replacement for the GM part
number, right down to the gasket at the end instead of the check valve. The corvette guys say to put a little bit of lube of the filter end so the
spring doesn't bind the filter as it turns?

> Sir, is your filter pointing forward toward radiator or sideways toward valve cover? You may be using wrong filter.there should be room for a
> filter and a spring.
>
>
>

> > Anyone ever come across a twisted fuel filter in their carb? The filter i removed from my carb during rebuild had the end twisted and skewed
> > sideways a bit [which was possibly the cause of my off idle bog/amost stall]... after my rebuild or refresh the carb is lean [no noticeable vacuum
> > leaks by normal tests and appears to be running out of fuel in the mid throttle position. I haven't verified yet but i would bet a beer the filter
> > is twisted again and its preventing full fuel flow from entering the carb under low pump RPM.
> >
> > Also their has been talk on the Vette forums about a sintered bronze filter instead....anyone know of such a beast for the motorhome?

--
Rich Mondor,

Brockville, ON

77 Hughes 2600

 

[john r. lebetski]

If an off idle flat spot is the issue I doubt that the bowl level being low due to restricted filter is the issue. Usually the level recovers during
low demand. You can prove it’s not the filter If it pulls hard at full throttle and does not go flat after a few seconds. Hard to say how much
throttle you are giving it but my guesses are
1) float level set a little too low
2) bad or wrong P/N accelerator pump in carb
3) stuck closed (down) power piston on primaries.
4) clogged pullover slots circuit on primaries
5) non operative or miss patched vac advance. Factory would be no vac advance at idle, then vac advance in effect right where your problem is off
idle. Without this added timing it would be flat off idle.
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[6cuda61]

John,
Pump shot is awesome and it keeps the motor running [think double tap to get moving from decel] but if you slowly get into the throttle it will bog or
die.....if i keep the choke blade closed about 1/4 to 1/3 way it runs perfect, so i suspect its lean possibly from a vacuum leak that i can't find
[tested every hose, intake etc with brake cleaner/carb cleaner/penetrating fluid etc but cant find it] or i need more idle mixture [currently about
3.5 turns out, which is were the PO had it set but the service manual says to start at 4 turns so i think its lean].

It feels like it starving for fuel off idle and into early midrange hence my question about filters as the originally installed filter by the PO was
twisted....i know this will cause fuel starvation under load as that is what the guys are reporting on the Vette side.

Sadly i cant mess with it that much as i'm waiting for exhaust manifold donut gaskets as mine are, well lets just leave it at PO improvised. I do love
the sound of a motor on open exhaust but its no help for tuning a carb and these coaches get so hot with the mufflers under the forward section that
without driving and no air flow the aluminum step bars get really hot making it hard to work.

> If an off idle flat spot is the issue I doubt that the bowl level being low due to restricted filter is the issue. Usually the level recovers
> during low demand. You can prove it’s not the filter If it pulls hard at full throttle and does not go flat after a few seconds. Hard to say how
> much throttle you are giving it but my guesses are
> 1) float level set a little too low
> 2) bad or wrong P/N accelerator pump in carb
> 3) stuck closed (down) power piston on primaries.
> 4) clogged pullover slots circuit on primaries
> 5) non operative or miss patched vac advance. Factory would be no vac advance at idle, then vac advance in effect right where your problem is off
> idle. Without this added timing it would be flat off idle.

--
Rich Mondor,

Brockville, ON

77 Hughes 2600

 

[les burt]

The filter is always a bit longer than the cavity it fits. When you tighten the housing, the filter is slightly compressed and often twists. I bet the filters we find today are all made in China and possibly a bit too long. I wouldn’t worry about a slight deformation.

Les Burt
Montreal
'75 Eleganza 26'

>
> If an off idle flat spot is the issue I doubt that the bowl level being low due to restricted filter is the issue. Usually the level recovers during
> low demand. You can prove it’s not the filter If it pulls hard at full throttle and does not go flat after a few seconds. Hard to say how much
> throttle you are giving it but my guesses are
> 1) float level set a little too low
> 2) bad or wrong P/N accelerator pump in carb
> 3) stuck closed (down) power piston on primaries.
> 4) clogged pullover slots circuit on primaries
> 5) non operative or miss patched vac advance. Factory would be no vac advance at idle, then vac advance in effect right where your problem is off
> idle. Without this added timing it would be flat off idle.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

 

[john r. lebetski]

Ok sounds like you can eliminate item 2 on my list but the other items need to be confirmed. To set the idle mixture, on warm engine find max RPM by
adjusting each screw slowly to the center point of max RPM. Then lean each side just to the point where RPM wants to start to drop but does not. You
may have to reset idle speed mid process. You can leave it there at max RPM just before drop, or do it by the book, which is turn in one screw for 25
RPM drop and other screw for 25 RPM. You want 50 RPM total drop which should only be 1/8 turn in or so if you were at the lean edge before. If yours
is way off it could be a problem at tip in as the idle circuit still contributes and transitions out not just a hard On/Off thing.
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[Jim Hupy]

Why is there so much concern about idle speed and mixture? Set up your
basic idle somewhere between 600 -750 rpm. Adjust for lean/rich, correct
for speed, and leave it be. You should not idle your engine any more than
absolutely necessary. Doesn't get enough upper end lube at idle speed.
Start the engine when cold, run until the choke opens, put it in gear and
drive it slowly until the coolant is warm, then drive normally. When you
stop, shut it off.
Jim Hupy
Salem, Oregon

On Tue, Jun 23, 2020, 7:34 AM John R. Lebetski via Gmclist <

> Ok sounds like you can eliminate item 2 on my list but the other items
> need to be confirmed. To set the idle mixture, on warm engine find max RPM
> by
> adjusting each screw slowly to the center point of max RPM. Then lean each
> side just to the point where RPM wants to start to drop but does not. You
> may have to reset idle speed mid process. You can leave it there at max
> RPM just before drop, or do it by the book, which is turn in one screw for
> 25
> RPM drop and other screw for 25 RPM. You want 50 RPM total drop which
> should only be 1/8 turn in or so if you were at the lean edge before. If
> yours
> is way off it could be a problem at tip in as the idle circuit still
> contributes and transitions out not just a hard On/Off thing.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[6cuda61]

Jim, i don't idle the engine normally any more than i have to but when one is trying to diagnose operational problems their really is not much choice
in the matter.

This coach has always fallen flat on its face to the point of stalling when you get into the throttle from a stop and double pumping the pedal for the
extra shot of fuel appon start of accel is the only way to get moving. I rebuilt the carb and the problem still exists [along with the added possible
vacuum leak or lean mixture]...the only visible issue when i tore the carb down was the twisted filter and a little bit of junk in the bowl, so trying
to find out why the twisted filter and upon research the same diving conditions have happened to a few of the corvette guys and the culprit was a
twisted filter.

> Why is there so much concern about idle speed and mixture? Set up your
> basic idle somewhere between 600 -750 rpm. Adjust for lean/rich, correct
> for speed, and leave it be. You should not idle your engine any more than
> absolutely necessary. Doesn't get enough upper end lube at idle speed.
> Start the engine when cold, run until the choke opens, put it in gear and
> drive it slowly until the coolant is warm, then drive normally. When you
> stop, shut it off.
> Jim Hupy
> Salem, Oregon
>
> On Tue, Jun 23, 2020, 7:34 AM John R. Lebetski via Gmclist <

>
> > Ok sounds like you can eliminate item 2 on my list but the other items
> > need to be confirmed. To set the idle mixture, on warm engine find max RPM
> > by
> > adjusting each screw slowly to the center point of max RPM. Then lean each
> > side just to the point where RPM wants to start to drop but does not. You
> > may have to reset idle speed mid process. You can leave it there at max
> > RPM just before drop, or do it by the book, which is turn in one screw for
> > 25
> > RPM drop and other screw for 25 RPM. You want 50 RPM total drop which
> > should only be 1/8 turn in or so if you were at the lean edge before. If
> > yours
> > is way off it could be a problem at tip in as the idle circuit still
> > contributes and transitions out not just a hard On/Off thing.
> > --
> > John Lebetski
> > Woodstock, IL
> > 77 Eleganza II
> >
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

--
Rich Mondor,

Brockville, ON

77 Hughes 2600

 

[Jim Hupy]

A corvette is not a GMC. Flat spot off idle (low speed tip-in) is USUALLY
caused by one of two things. Excessively LEAN MIXTURE, or vacuum leak.
Could also be contributed to, by retarded spark timing, low float bowl
level, or warped carb base (very, very common in Quadrajet Carburetors.)
Cause? Overtightening the 4 corners. There is a Phillip's head screw in the
center of the iron throttle body casting that screws into the pot metal
float bowl. Often times, it is quite loose. The quadrajet carb is not
anywhere as complex as many believe it to be. Be very sure that yours is
the exact part number for your GMC. Close does not count. Dick Paterson
won't even rebuild a carb if it is not an OEM one, and I don't blame him
one bit.
Jim Hupy
Salem, Oregon

On Tue, Jun 23, 2020, 9:06 AM 6cuda6--- via Gmclist
wrote:

> Jim, i don't idle the engine normally any more than i have to but when one
> is trying to diagnose operational problems their really is not much choice
> in the matter.
>
> This coach has always fallen flat on its face to the point of stalling
> when you get into the throttle from a stop and double pumping the pedal for
> the
> extra shot of fuel appon start of accel is the only way to get moving. I
> rebuilt the carb and the problem still exists [along with the added possible
> vacuum leak or lean mixture]...the only visible issue when i tore the carb
> down was the twisted filter and a little bit of junk in the bowl, so trying
> to find out why the twisted filter and upon research the same diving
> conditions have happened to a few of the corvette guys and the culprit was a
> twisted filter.
>
>

> > Why is there so much concern about idle speed and mixture? Set up your
> > basic idle somewhere between 600 -750 rpm. Adjust for lean/rich, correct
> > for speed, and leave it be. You should not idle your engine any more than
> > absolutely necessary. Doesn't get enough upper end lube at idle speed.
> > Start the engine when cold, run until the choke opens, put it in gear and
> > drive it slowly until the coolant is warm, then drive normally. When you
> > stop, shut it off.
> > Jim Hupy
> > Salem, Oregon
> >
> > On Tue, Jun 23, 2020, 7:34 AM John R. Lebetski via Gmclist <

> >
> > > Ok sounds like you can eliminate item 2 on my list but the other items
> > > need to be confirmed. To set the idle mixture, on warm engine find
> max RPM
> > > by
> > > adjusting each screw slowly to the center point of max RPM. Then lean
> each
> > > side just to the point where RPM wants to start to drop but does not.
> You
> > > may have to reset idle speed mid process. You can leave it there at
> max
> > > RPM just before drop, or do it by the book, which is turn in one
> screw for
> > > 25
> > > RPM drop and other screw for 25 RPM. You want 50 RPM total drop which
> > > should only be 1/8 turn in or so if you were at the lean edge before.
> If
> > > yours
> > > is way off it could be a problem at tip in as the idle circuit still
> > > contributes and transitions out not just a hard On/Off thing.
> > > --
> > > John Lebetski
> > > Woodstock, IL
> > > 77 Eleganza II
> > >
> > >
> > > _______________________________________________
> > > GMCnet mailing list
> > > Unsubscribe or Change List Options:
> > > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> > >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> --
> Rich Mondor,
>
> Brockville, ON
>
> 77 Hughes 2600
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[Bob Dunahugh]

There is a spring that keeps the filter up against the fitting that you screw into the base. As you install the filter. The filter is fairly stout. The spring tention is very light. Thus, the filter cannot get twisted during installation. The spring will put a very light twist action on the filter. After installed.
I never saw water in the carb. But when I've found filters that came apart. I then drained the tanks at the drain plugs. And tilted them to get as much out as possible. Then filled the tanks with E-15. Put a new carb filter in. Problem went away. I've had this happen twice. Thus, I ASSUMED that it was water in the gas. BUT. We all know about ASSUME. For those that may not know. ASS out of U and ME both. Open for other thoughts.
Bob Dunahugh
78 Royale since 2003

________________________________
From: Bob Dunahugh
Sent: Monday, June 22, 2020 11:43 PM
To: gmclist
Subject: RE: Twisted fuel filter?

GM called for a 2-micron filters in the carb. Yes. GM did have a bronze filter. But I have serious droughts that it's also 2 micron. The Q jet must have that 2-micron filter. Most in line filters are 20 micron. Some owners take the Q jet filter out. And think an in line filter will do the job. NO. It will not. But it will give you carb problems.
As to the twist. Most of those paper carb filters. Used a water base adhesive. Every time that I've found the filter coming apart like you're talking about. I found water in the tank. Something to think about.
Bob Dunahugh
78 Royale since 2003.
4 real COPO Yenkos

 

[6cuda61]

Jim,
Were the 77 403 and 455 carbs the same? The reason i ask is you said 3 lower plate screws, mine only had 2.....

> A corvette is not a GMC. Flat spot off idle (low speed tip-in) is USUALLY
> caused by one of two things. Excessively LEAN MIXTURE, or vacuum leak.
> Could also be contributed to, by retarded spark timing, low float bowl
> level, or warped carb base (very, very common in Quadrajet Carburetors.)
> Cause? Overtightening the 4 corners. There is a Phillip's head screw in the
> center of the iron throttle body casting that screws into the pot metal
> float bowl. Often times, it is quite loose. The quadrajet carb is not
> anywhere as complex as many believe it to be. Be very sure that yours is
> the exact part number for your GMC. Close does not count. Dick Paterson
> won't even rebuild a carb if it is not an OEM one, and I don't blame him
> one bit.
> Jim Hupy
> Salem, Oregon
>
> On Tue, Jun 23, 2020, 9:06 AM 6cuda6--- via Gmclist

>
> > Jim, i don't idle the engine normally any more than i have to but when one
> > is trying to diagnose operational problems their really is not much choice
> > in the matter.
> >
> > This coach has always fallen flat on its face to the point of stalling
> > when you get into the throttle from a stop and double pumping the pedal for
> > the
> > extra shot of fuel appon start of accel is the only way to get moving. I
> > rebuilt the carb and the problem still exists [along with the added possible
> > vacuum leak or lean mixture]...the only visible issue when i tore the carb
> > down was the twisted filter and a little bit of junk in the bowl, so trying
> > to find out why the twisted filter and upon research the same diving
> > conditions have happened to a few of the corvette guys and the culprit was a
> > twisted filter.
> >
> >

> >> Why is there so much concern about idle speed and mixture? Set up your
> >> basic idle somewhere between 600 -750 rpm. Adjust for lean/rich, correct
> >> for speed, and leave it be. You should not idle your engine any more than
> >> absolutely necessary. Doesn't get enough upper end lube at idle speed.
> >> Start the engine when cold, run until the choke opens, put it in gear and
> >> drive it slowly until the coolant is warm, then drive normally. When you
> >> stop, shut it off.
> >> Jim Hupy
> >> Salem, Oregon
> >>

> >>
> >>> Ok sounds like you can eliminate item 2 on my list but the other items
> >>> need to be confirmed. To set the idle mixture, on warm engine find
> > max RPM
> >>> by
> >>> adjusting each screw slowly to the center point of max RPM. Then lean
> > each
> >>> side just to the point where RPM wants to start to drop but does not.
> > You
> >>> may have to reset idle speed mid process. You can leave it there at
> > max
> >>> RPM just before drop, or do it by the book, which is turn in one
> > screw for
> >>> 25
> >>> RPM drop and other screw for 25 RPM. You want 50 RPM total drop which
> >>> should only be 1/8 turn in or so if you were at the lean edge before.
> > If
> >>> yours
> >>> is way off it could be a problem at tip in as the idle circuit still
> >>> contributes and transitions out not just a hard On/Off thing.
> >>> --
> >>> John Lebetski
> >>> Woodstock, IL
> >>> 77 Eleganza II
> >>>
> >>>
> >>> _______________________________________________
> >>> GMCnet mailing list
> >>> Unsubscribe or Change List Options:
> >>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >>>
> >> _______________________________________________
> >> GMCnet mailing list
> >> Unsubscribe or Change List Options:
> >> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> >
> > --
> > Rich Mondor,
> >
> > Brockville, ON
> >
> > 77 Hughes 2600
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

--
Rich Mondor,

Brockville, ON

77 Hughes 2600

 

[Jim Hupy]

No, the carbs are not the same.
1. There is the one fitted to the 73 - late 76
455.
2. There is the one fitted to the late 76-78 49 states (excluding
California). 403
3. Then, there is the one fitted to the 76 California 403.
4. There is one fitted to the 77 California 403.
5. There is one fitted to the 78 California 403.
There may be others, as well. All the part numbers can be found in either
the 73-76 Shop manual, or the Supplemental manual for the late 76 - 78, as
well as California. Look in the emissions section, not the fuel system
section. Takes some sorting, but it's all in there.
Do not rely upon anyones memory of the correct part numbers. Check the
books, and compare the number you have on your carb to verify that you have
the correct carb.

On Tue, Jun 23, 2020, 10:18 AM 6cuda6--- via Gmclist <

> Jim,
> Were the 77 403 and 455 carbs the same? The reason i ask is you said 3
> lower plate screws, mine only had 2.....
>
>
>

> > A corvette is not a GMC. Flat spot off idle (low speed tip-in) is USUALLY
> > caused by one of two things. Excessively LEAN MIXTURE, or vacuum leak.
> > Could also be contributed to, by retarded spark timing, low float bowl
> > level, or warped carb base (very, very common in Quadrajet Carburetors.)
> > Cause? Overtightening the 4 corners. There is a Phillip's head screw in
> the
> > center of the iron throttle body casting that screws into the pot metal
> > float bowl. Often times, it is quite loose. The quadrajet carb is not
> > anywhere as complex as many believe it to be. Be very sure that yours is
> > the exact part number for your GMC. Close does not count. Dick Paterson
> > won't even rebuild a carb if it is not an OEM one, and I don't blame him
> > one bit.
> > Jim Hupy
> > Salem, Oregon
> >
> > On Tue, Jun 23, 2020, 9:06 AM 6cuda6--- via Gmclist

> >
> > > Jim, i don't idle the engine normally any more than i have to but
> when one
> > > is trying to diagnose operational problems their really is not much
> choice
> > > in the matter.
> > >
> > > This coach has always fallen flat on its face to the point of stalling
> > > when you get into the throttle from a stop and double pumping the
> pedal for
> > > the
> > > extra shot of fuel appon start of accel is the only way to get
> moving. I
> > > rebuilt the carb and the problem still exists [along with the added
> possible
> > > vacuum leak or lean mixture]...the only visible issue when i tore the
> carb
> > > down was the twisted filter and a little bit of junk in the bowl, so
> trying
> > > to find out why the twisted filter and upon research the same diving
> > > conditions have happened to a few of the corvette guys and the
> culprit was a
> > > twisted filter.
> > >
> > >

> > >> Why is there so much concern about idle speed and mixture? Set up
> your
> > >> basic idle somewhere between 600 -750 rpm. Adjust for lean/rich,
> correct
> > >> for speed, and leave it be. You should not idle your engine any more
> than
> > >> absolutely necessary. Doesn't get enough upper end lube at idle
> speed.
> > >> Start the engine when cold, run until the choke opens, put it in
> gear and
> > >> drive it slowly until the coolant is warm, then drive normally. When
> you
> > >> stop, shut it off.
> > >> Jim Hupy
> > >> Salem, Oregon
> > >>
> > >> On Tue, Jun 23, 2020, 7:34 AM John R. Lebetski via Gmclist >

> > >>
> > >>> Ok sounds like you can eliminate item 2 on my list but the other
> items
> > >>> need to be confirmed. To set the idle mixture, on warm engine find
> > > max RPM
> > >>> by
> > >>> adjusting each screw slowly to the center point of max RPM. Then
> lean
> > > each
> > >>> side just to the point where RPM wants to start to drop but does
> not.
> > > You
> > >>> may have to reset idle speed mid process. You can leave it there at
> > > max
> > >>> RPM just before drop, or do it by the book, which is turn in one
> > > screw for
> > >>> 25
> > >>> RPM drop and other screw for 25 RPM. You want 50 RPM total drop
> which
> > >>> should only be 1/8 turn in or so if you were at the lean edge
> before.
> > > If
> > >>> yours
> > >>> is way off it could be a problem at tip in as the idle circuit
> still
> > >>> contributes and transitions out not just a hard On/Off thing.
> > >>> --
> > >>> John Lebetski
> > >>> Woodstock, IL
> > >>> 77 Eleganza II
> > >>>
> > >>>
> > >>> _______________________________________________
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> > >>>
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> > >
> > >
> > > --
> > > Rich Mondor,
> > >
> > > Brockville, ON
> > >
> > > 77 Hughes 2600
> > >
> > > _______________________________________________
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>
> --
> Rich Mondor,
>
> Brockville, ON
>
> 77 Hughes 2600
>
> _______________________________________________
> GMCnet mailing list
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[6cuda61]

Just checking because that's what i thought....

> No, the carbs are not the same.
> 1. There is the one fitted to the 73 - late 76
> 455.
> 2. There is the one fitted to the late 76-78 49 states (excluding
> California). 403
> 3. Then, there is the one fitted to the 76 California 403.
> 4. There is one fitted to the 77 California 403.
> 5. There is one fitted to the 78 California 403.
> There may be others, as well. All the part numbers can be found in either
> the 73-76 Shop manual, or the Supplemental manual for the late 76 - 78, as
> well as California. Look in the emissions section, not the fuel system
> section. Takes some sorting, but it's all in there.
> Do not rely upon anyones memory of the correct part numbers. Check the
> books, and compare the number you have on your carb to verify that you have
> the correct carb.
>
> On Tue, Jun 23, 2020, 10:18 AM 6cuda6--- via Gmclist <

>
> > Jim,
> > Were the 77 403 and 455 carbs the same? The reason i ask is you said 3
> > lower plate screws, mine only had 2.....
> >
> >
> >

> >> A corvette is not a GMC. Flat spot off idle (low speed tip-in) is USUALLY
> >> caused by one of two things. Excessively LEAN MIXTURE, or vacuum leak.
> >> Could also be contributed to, by retarded spark timing, low float bowl
> >> level, or warped carb base (very, very common in Quadrajet Carburetors.)
> >> Cause? Overtightening the 4 corners. There is a Phillip's head screw in
> > the
> >> center of the iron throttle body casting that screws into the pot metal
> >> float bowl. Often times, it is quite loose. The quadrajet carb is not
> >> anywhere as complex as many believe it to be. Be very sure that yours is
> >> the exact part number for your GMC. Close does not count. Dick Paterson
> >> won't even rebuild a carb if it is not an OEM one, and I don't blame him
> >> one bit.
> >> Jim Hupy
> >> Salem, Oregon
> >>
> >> On Tue, Jun 23, 2020, 9:06 AM 6cuda6--- via Gmclist

> >>
> >>> Jim, i don't idle the engine normally any more than i have to but
> > when one
> >>> is trying to diagnose operational problems their really is not much
> > choice
> >>> in the matter.
> >>>
> >>> This coach has always fallen flat on its face to the point of stalling
> >>> when you get into the throttle from a stop and double pumping the
> > pedal for
> >>> the
> >>> extra shot of fuel appon start of accel is the only way to get
> > moving. I
> >>> rebuilt the carb and the problem still exists [along with the added
> > possible
> >>> vacuum leak or lean mixture]...the only visible issue when i tore the
> > carb
> >>> down was the twisted filter and a little bit of junk in the bowl, so
> > trying
> >>> to find out why the twisted filter and upon research the same diving
> >>> conditions have happened to a few of the corvette guys and the
> > culprit was a
> >>> twisted filter.
> >>>
> >>>

> >>>> Why is there so much concern about idle speed and mixture? Set up
> > your
> >>>> basic idle somewhere between 600 -750 rpm. Adjust for lean/rich,
> > correct
> >>>> for speed, and leave it be. You should not idle your engine any more
> > than
> >>>> absolutely necessary. Doesn't get enough upper end lube at idle
> > speed.
> >>>> Start the engine when cold, run until the choke opens, put it in
> > gear and
> >>>> drive it slowly until the coolant is warm, then drive normally. When
> > you
> >>>> stop, shut it off.
> >>>> Jim Hupy
> >>>> Salem, Oregon
> >>>>
> >>>> On Tue, Jun 23, 2020, 7:34 AM John R. Lebetski via Gmclist >

> >>>>
> >>>> > Ok sounds like you can eliminate item 2 on my list but the other
> > items
> >>>> > need to be confirmed. To set the idle mixture, on warm engine find
> >>> max RPM
> >>>> > by
> >>>> > adjusting each screw slowly to the center point of max RPM. Then
> > lean
> >>> each
> >>>> > side just to the point where RPM wants to start to drop but does
> > not.
> >>> You
> >>>> > may have to reset idle speed mid process. You can leave it there at
> >>> max
> >>>> > RPM just before drop, or do it by the book, which is turn in one
> >>> screw for
> >>>> > 25
> >>>> > RPM drop and other screw for 25 RPM. You want 50 RPM total drop
> > which
> >>>> > should only be 1/8 turn in or so if you were at the lean edge
> > before.
> >>> If
> >>>> > yours
> >>>> > is way off it could be a problem at tip in as the idle circuit
> > still
> >>>> > contributes and transitions out not just a hard On/Off thing.
> >>>> > --
> >>>> > John Lebetski
> >>>> > Woodstock, IL
> >>>> > 77 Eleganza II
> >>>> >
> >>>> >
> >>>> > _______________________________________________
> >>>> > GMCnet mailing list
> >>>> > Unsubscribe or Change List Options:
> >>>> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >>>> >
> >>>> _______________________________________________
> >>>> GMCnet mailing list
> >>>> Unsubscribe or Change List Options:
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> >>>
> >>>
> >>> --
> >>> Rich Mondor,
> >>>
> >>> Brockville, ON
> >>>
> >>> 77 Hughes 2600
> >>>
> >>> _______________________________________________
> >>> GMCnet mailing list
> >>> Unsubscribe or Change List Options:
> >>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >>>
> >> _______________________________________________
> >> GMCnet mailing list
> >> Unsubscribe or Change List Options:
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> >
> >
> > --
> > Rich Mondor,
> >
> > Brockville, ON
> >
> > 77 Hughes 2600
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> _______________________________________________
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--
Rich Mondor,

Brockville, ON

77 Hughes 2600

 

[6cuda61]

Well i guess once i get the exhaust donut gaskets and install them then we can try to get it running properly again. Worse case the carb comes back
off and i'll pop it open again.

> There is a spring that keeps the filter up against the fitting that you screw into the base. As you install the filter. The filter is fairly
> stout. The spring tention is very light. Thus, the filter cannot get twisted during installation. The spring will put a very light twist action on
> the filter. After installed.
> I never saw water in the carb. But when I've found filters that came apart. I then drained the tanks at the drain plugs. And tilted them to get as
> much out as possible. Then filled the tanks with E-15. Put a new carb filter in. Problem went away. I've had this happen twice. Thus, I ASSUMED that
> it was water in the gas. BUT. We all know about ASSUME. For those that may not know. ASS out of U and ME both. Open for other thoughts.
> Bob Dunahugh
> 78 Royale since 2003
>
> ________________________________
> From: Bob Dunahugh
> Sent: Monday, June 22, 2020 11:43 PM
> To: gmclist
> Subject: RE: Twisted fuel filter?
>
> GM called for a 2-micron filters in the carb. Yes. GM did have a bronze filter. But I have serious droughts that it's also 2 micron. The Q jet
> must have that 2-micron filter. Most in line filters are 20 micron. Some owners take the Q jet filter out. And think an in line filter will do the
> job. NO. It will not. But it will give you carb problems.
> As to the twist. Most of those paper carb filters. Used a water base adhesive. Every time that I've found the filter coming apart like you're
> talking about. I found water in the tank. Something to think about.
> Bob Dunahugh
> 78 Royale since 2003.
> 4 real COPO Yenkos
> _______________________________________________
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--
Rich Mondor,

Brockville, ON

77 Hughes 2600