Carburetors

[darren paget]

A question on rebuilding, if I may? In previous posts it appears that
when rebuilding the Q-jet I should go up two sizes on the primary jets.
Is this true? If I have a stock carb with size 70 primaries, does this
mean I go up to 72? My GM is a 1976. If you look at the stock numbers
for a '77' The primaries get changed from 68 primaries to 70. This does
not follow unless all 77's had 403's. Is there anybody who can give me
a definitive answer on this? You guys who have had this done, can you
tell me what you did to yours? Thank you. Darren

 

[patrick flowers]

>
> A question on rebuilding, if I may? In previous posts it appears that
> when rebuilding the Q-jet I should go up two sizes on the primary jets.
> Is this true? If I have a stock carb with size 70 primaries, does this
> mean I go up to 72? My GM is a 1976. If you look at the stock numbers
> for a '77' The primaries get changed from 68 primaries to 70. This does
> not follow unless all 77's had 403's. Is there anybody who can give me
> a definitive answer on this? You guys who have had this done, can you
> tell me what you did to yours? Thank you. Darren

Darren,

AFAIK, all 77's and 78's had 403 Olds engines. There may have been some
overlap due to the vagaries of the model year system as it was applied
to the motorhomes. My 73 had 70 primaries and I changed them to 72's.
Not much data yet as I've only driven it around the block so far. Also
changed out my points-type distributor for a Bob Lamey rebuilt HEI with
Springfield wires and Rapidfire plugs. It runs like a sewing machine
now - even my wife, definitely not the mechanic type, comment on how
smoothly it was idling.

Patrick
- --
Patrick Flowers
Mailtoatrick

The GMC Motorhome Page
http://www.gmcmotorhome.com

 

[thomas g. warner]

Rule of thumb is to go up 2 jet sizes. for example if you had 70 primaries
go to a 74, and also go up 2 primary rod sizes, for example if it was .054
go to .047.
the problem is that you probably do not know if you have the correct or
original carb.

I watch the plugs to see how it is running.

>
>A question on rebuilding, if I may? In previous posts it appears that
>when rebuilding the Q-jet I should go up two sizes on the primary jets.
>Is this true? If I have a stock carb with size 70 primaries, does this
>mean I go up to 72? My GM is a 1976. If you look at the stock numbers
>for a '77' The primaries get changed from 68 primaries to 70. This does
>not follow unless all 77's had 403's. Is there anybody who can give me
>a definitive answer on this? You guys who have had this done, can you
>tell me what you did to yours? Thank you. Darren
>
>
>
Tom & Marg Warner
Vernon Center NY
1976 palmbeach
"The beautiful Mohawk Vally"

 

[thomas g. warner]

patrick many of the 403's have been changed out by previous owners so you
can not tell by the year. I have seen 77's and 78's with 455's

>>
>> A question on rebuilding, if I may? In previous posts it appears that
>> when rebuilding the Q-jet I should go up two sizes on the primary jets.
>> Is this true? If I have a stock carb with size 70 primaries, does this
>> mean I go up to 72? My GM is a 1976. If you look at the stock numbers
>> for a '77' The primaries get changed from 68 primaries to 70. This does
>> not follow unless all 77's had 403's. Is there anybody who can give me
>> a definitive answer on this? You guys who have had this done, can you
>> tell me what you did to yours? Thank you. Darren
>
>Darren,
>
>AFAIK, all 77's and 78's had 403 Olds engines. There may have been some
>overlap due to the vagaries of the model year system as it was applied
>to the motorhomes. My 73 had 70 primaries and I changed them to 72's.
>Not much data yet as I've only driven it around the block so far. Also
>changed out my points-type distributor for a Bob Lamey rebuilt HEI with
>Springfield wires and Rapidfire plugs. It runs like a sewing machine
>now - even my wife, definitely not the mechanic type, comment on how
>smoothly it was idling.
>
>Patrick
>--
>Patrick Flowers
>Mailtoatrick
>
>The GMC Motorhome Page
>http://www.gmcmotorhome.com
>
>
Tom & Marg Warner
Vernon Center NY
1976 palmbeach
"The beautiful Mohawk Vally"

 

[mike finnicum]

FYI

Just had my carb rebuilt by an outfit in Tampa (went thru Jim
Bounds),
job was fantastic, was even "wet" tested and adjusted before it
was shipped.

Just bolted on - coach runs great. Jim says they fully understand
how to rebuild it for our GMCs.

I shipped mine to Jim on Tuesday, I had it back on the coach the
same Friday! That's service.

During my first 800 miles on new carb my mileage has increased by
1 mpg (I also replaced ALL of my vacuum lines). Sure hope it
stays
there. Engine is so smooth it's scarry. It also helped with some
"pinging" I was having before the rebuild.

Call Jim at 877-ASK4GMC for details.

Mike

- -----Original Message-----
From: owner-gmcmotorhome
[mailtowner-gmcmotorhome]On Behalf Of Patrick
Flowers
Sent: Monday, May 24, 1999 8:36 AM
To: gmcmotorhome
Subject: Re: GMC: Carburetors

>
> A question on rebuilding, if I may? In previous posts it
appears that
> when rebuilding the Q-jet I should go up two sizes on the
primary jets.
> Is this true? If I have a stock carb with size 70 primaries,
does this
> mean I go up to 72? My GM is a 1976. If you look at the stock
numbers
> for a '77' The primaries get changed from 68 primaries to 70.
This does
> not follow unless all 77's had 403's. Is there anybody who can
give me
> a definitive answer on this? You guys who have had this done,
can you
> tell me what you did to yours? Thank you. Darren

Darren,

AFAIK, all 77's and 78's had 403 Olds engines. There may have
been some
overlap due to the vagaries of the model year system as it was
applied
to the motorhomes. My 73 had 70 primaries and I changed them to
72's.
Not much data yet as I've only driven it around the block so far.
Also
changed out my points-type distributor for a Bob Lamey rebuilt
HEI with
Springfield wires and Rapidfire plugs. It runs like a sewing
machine
now - even my wife, definitely not the mechanic type, comment on
how
smoothly it was idling.

Patrick
- --
Patrick Flowers
Mailtoatrick

The GMC Motorhome Page
http://www.gmcmotorhome.com

 

[david l greenberg]

not follow unless all 77's had 403's. Is there anybody who can give
>me
>> a definitive answer on this?
>
>AFAIK, all 77's and 78's had 403 Olds engines.

Sorry...no cigar! Early '77s had the big block thu TZE's 167V101284,
TZE337V101287 and TZE367V101312

David Lee Greenberg
GMC Motorhome Registry
FMCA Voice Mail: 800.445.1732
F22009