Starting (reply)

[mark grady]

I'm no expert, but just a for what it's worth... There are two peened over
'disks' in the bottom of a Q-jet (your carburetor) that don't seal very
well. They let the residual gas in the bowl leak out and it runs in the
manifold rather than stay where it's supposed to.

If you epoxy those tight, your problems will be lessened or go away. At
least it worked for me. You can fix that problem during a good rebuild, and
there have been a number of names that folks put on this list that are
likely high quality shops.

Also, you might consider whether the gas you're buying has some alcohol
content. It's more volatile (evaporates faster) which would reduce the
residual gas in the carb after a period of non-use.

If those answers don't make sense, tell yourself this: longer periods of no
fire cranking allow oil pressure to build in the engine and ensures a longer
life.

I don't have fuel injection, so on my first start of the season I always
wait until the oil pressure gauge starts to move before I punch the pedal to
set the auto choke and let the ole General fire up.

Just a thought.

Mark Grady
'77 Kingsley
North Webster, IN
mgrady

> -----Original Message-----
> From: owner-gmcmotorhome
> [mailtowner-gmcmotorhome]On Behalf Of
> hdavis
> Sent: Friday, November 13, 1998 5:18 PM
> To: gmcmotorhome
> Subject: Re: GMC: Starting
>
>

> >
> >Is it normal that the motorhome has to crank several seconds,
> 10-15, before
> >starting?

{snip}

 

[thomas g. warner]

Here is some more information that I had on the hard starting problem;

Stage 1- #JQJETS1, #JQJS1

A Stage1 Quadrajet begins with a complete disassembly, cleaning and
inspection procedure. The casting plugs are sealed with epoxy to prevent
leakdown into the intake manifold. All circuits are checked for proper
sizing and the calibration is checked for proper jets, primary metering rods
and secondary metering rods. The carburetor is then reassembled using the
highest quality componets with a new float, choke pull-off and bronze bushed
throttle shafts. A Stage1 is intended to restore factory stock performance
to your Q-Jet.

Rochester Quadrajet Common Problems and Decoding
by George Nenadovich
The Rochester carb is the most common carb found in GM cars and trucks from
the 1960's to the mid-1980's when they were replaced by fuel injection
units. If the carb is maintained properly, it will deliver years of service.
There are a few problems with the Rochester carbs as they get older and/or
are not maintained.
A common problem is the fuel filter inside the fuel inlet housing becomes
plugged with debris from dirty gasoline. This prevents the float bowl from
filling quickly and results in poor engine performance. This filter is not
an ideal candidate since it is made of paper and can not be seen unless the
filter is removed from the housing. The best filter to use is a glass filter
connected in-line between the fuel pump and carb. This filter allows you to
see if the fuel pump is working as well as if there is any debris in the fuel.
Another problem is the cam that raises the secondary metering rods when the
air valves open. This small heart shaped plastic cam is located between the
secondary air valves on the air valve shaft. It is common for this part to
break preventing proper operation of the secondary air valves leading to a bog.
Another problem associated with the secondary air valves is the vacuum
secondary break. This small vacuum break is located on the passenger side of
the carb. These small diaphragms rupture after years of exposure to heat and
result in the secondary air valves flopping open causing a bog.
A couple of other problems but not common are the carb being bolted to the
intake with excessive torque and fuel well plugs leaking. If the carb is
overtightened with the four bolts mounting it to the intake the air horn
will be bent creating fuel leaks and vacuum leaks. Always change the base
gasket when installing a rebuilt carb for it to create an air-tight seal
between the carb and intake. The fuel well plugs can leak and the best way
to fix them is to use an epoxy to seal both wells. The wells are located
under the bottom of the fuel metering rods.

Rochester Quadrajet Number Decoding
All Quadrajet carbs have numbers stamped on them on the driver's side rear
secondary. It is visible when the secondary throttle actuator is opened or
the carb is held at an angle. These numbers, 7 digits, indicate what engine
the carb is from as well as manual or automatic transmissions, California
emissions carb.
For example, the carb #7040246, indicates several pieces of information. The
fourth digit, 0, indicates the year, 1970. The sixth digit indicates the
make which in this case is 4 which is Buick. By checking the chart below, we
see the carb is a 1970 Buick 455 Stage 1 carburetor.
The sixth digit can be one of the following depending on make:
0,1,2 Chevrolet, GMC or truck
3 Cadillac
4 Buick
5 Oldsmobile
6 Pontiac
Buick Quadrajet Codes

YEAR CARB # ENGINE TRANS
- ---- ------- ------ -----
1967 7027148 400 M
7027146 400 A
7027149 400 w/A.I.R. M
7027147 400 w/A.I.R. A

1968 7028245 350 M
7028244 350 A
7028243 400 M
7028242 400 A
7028240 430 A

1969 7029245 350 M
7029244 350 A
7029243 400 M
7029242 400 A
7029240 430 A

1970 7040245 350 M
7040244 350 A
7040243 455 M
7040240 455 A
7040246 455 Stage 1 A or M
7040247 455 Riviera A

1971 7041245 350 M
7041544 350 A
7041243 455 M
7041540 455 A
7041242 455 Stage 1 A or M

1972 7042245 350 M
7042244 350 A
7042243 455 M
7042240 455 A
7042242 455 Stage 1 A or M

>I'm no expert, but just a for what it's worth... There are two peened over
>'disks' in the bottom of a Q-jet (your carburetor) that don't seal very
>well. They let the residual gas in the bowl leak out and it runs in the
>manifold rather than stay where it's supposed to.
>
>If you epoxy those tight, your problems will be lessened or go away. At
>least it worked for me. You can fix that problem during a good rebuild, and
>there have been a number of names that folks put on this list that are
>likely high quality shops.
>
>Also, you might consider whether the gas you're buying has some alcohol
>content. It's more volatile (evaporates faster) which would reduce the
>residual gas in the carb after a period of non-use.
>
>If those answers don't make sense, tell yourself this: longer periods of no
>fire cranking allow oil pressure to build in the engine and ensures a longer
>life.
>
>I don't have fuel injection, so on my first start of the season I always
>wait until the oil pressure gauge starts to move before I punch the pedal to
>set the auto choke and let the ole General fire up.
>
>Just a thought.
>
>Mark Grady
>'77 Kingsley
>North Webster, IN
>mgrady
>
>
>
>> -----Original Message-----
>> From: owner-gmcmotorhome
>> [mailtowner-gmcmotorhome]On Behalf Of
>> hdavis
>> Sent: Friday, November 13, 1998 5:18 PM
>> To: gmcmotorhome
>> Subject: Re: GMC: Starting
>>
>>

>> >
>> >Is it normal that the motorhome has to crank several seconds,
>> 10-15, before
>> >starting?
>
>{snip}
>
>
>
Tom & Marg Warner
Vernon Center NY
1976 palmbeach

 

[david sandford]

I quick question, you referred to a Quadrajet that had 4 metering rods.
The Quadrajet on a 74 Sequoia GMC-MH has a slightly different configuration.
This unit has metering rods only on the secondaries.

In our experience with a 77 Birchhaven which had the Quadrajet w/ 4 metering
rods, it was a lot easier to tune, and seemed to perform better to boot.
The secondaries were a lot "stronger." In addition the fuel economy was a
bit better, although that could be a function of the length and weight of
the coach, 23' vrs. 26'.

I was wondering if you, or anyone else, would know the number for the
Quadrajets that were installed on the later GMC-MH's.

On a related note, we installed a large canister type fuel filter ahead of
the Carb, and never really had any problems with rust or other junk.

The reason was were at the top of Spooner summit (HWY 50 between Lake Tahoe
and Carson City) we had two filters plug in quick succession, and that
wasn't the first experience.

Dave

- -----Original Message-----
From: Thomas G. Warner
To: gmcmotorhome
Date: Friday, November 13, 1998 5:26 PM
Subject: Re: GMC: Starting (reply)

Snip

>Rochester Quadrajet Number Decoding
>All Quadrajet carbs have numbers stamped on them on the driver's side rear
>secondary. It is visible when the secondary throttle actuator is opened or
>the carb is held at an angle. These numbers, 7 digits, indicate what engine
>the carb is from as well as manual or automatic transmissions, California
>emissions carb.
>For example, the carb #7040246, indicates several pieces of information.
The
>fourth digit, 0, indicates the year, 1970. The sixth digit indicates the
>make which in this case is 4 which is Buick. By checking the chart below,
we
>see the carb is a 1970 Buick 455 Stage 1 carburetor.
>The sixth digit can be one of the following depending on make:
> 0,1,2 Chevrolet, GMC or truck
> 3 Cadillac
> 4 Buick
> 5 Oldsmobile
> 6 Pontiac
>Buick Quadrajet Codes
>
> YEAR CARB # ENGINE TRANS
>---- ------- ------ -----
>1967 7027148 400 M
> 7027146 400 A
> 7027149 400 w/A.I.R. M
> 7027147 400 w/A.I.R. A
>
>1968 7028245 350 M
> 7028244 350 A
> 7028243 400 M
> 7028242 400 A
> 7028240 430 A
>
>1969 7029245 350 M
> 7029244 350 A
> 7029243 400 M
> 7029242 400 A
> 7029240 430 A
>
>1970 7040245 350 M
> 7040244 350 A
> 7040243 455 M
> 7040240 455 A
> 7040246 455 Stage 1 A or M
> 7040247 455 Riviera A
>
>1971 7041245 350 M
> 7041544 350 A
> 7041243 455 M
> 7041540 455 A
> 7041242 455 Stage 1 A or M
>
>1972 7042245 350 M
> 7042244 350 A
> 7042243 455 M
> 7042240 455 A
> 7042242 455 Stage 1 A or M
>
>
massive SNIP

 

[thomas g. warner]

Arch Cinnabar had a recommended mod of putting the filter just before the
fuel pump, adn removing the inline filter in the carb.

>Thomas
>
>Please dont do this. Leave the solid steel line from the pump
>to the carb alone. Put a filter back at the tanks.
>
>Take Care
>Arch
>
>> The best filter to use is a glass filter
>> connected in-line between the fuel pump and carb. This filter allows you to
>> see if the fuel pump is working as well as if there is any debris in the
>> fuel.
>>
>
>
Tom & Marg Warner
Vernon Center NY
1976 palmbeach