| [GMCnet] Primary venturis fuel drip at idle [message #333705] |
Tue, 19 June 2018 15:54  |
glwgmc
Messages: 1014
Registered: June 2004
Karma: 10
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Senior Member |
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Hi Dave,
My suggestion is to save yourself untold frustration by ditching all that stuff and install a modern self learning EFI. Your coach
will drive far more like a modern car.
All gain and no pain except for a one time $1000 hit to your bank account
Jerry
Jerry Work
Kerby, OR
......:::
ate: Tue, 19 Jun 2018 14:27:59 -0400
From: "Dave Stragand"
To:
Subject: [GMCnet] Primary venturis fuel drip at idle
Message-ID:
Content-Type: text/plain; charset="us-ascii"
Hi All,
I noticed today on my 1978 403 that the primary venturis both have a
steady splatter/drip of fuel at idle. I would get the same thing
occasionally on the professionally rebuilt QuadraJet on my '68 Caddy.
The cause was generally a sticking needle/seat/float - and a quick tap
or two on the carb from a rubber or plastic mallet would make everything
peachy again for a few months.
On my coach I have a quite a few more unknowns, such as:
- what the timing may currently be set to
- a number of disconnected and plugged vacuum lines
- if the idle mixture is correct
- overall engine condition
So I was looking for a bit of advice on what the most likely cause(s)
would be so I can check them in that order. My thoughts are (most
likely first, least likely last):
- debris stuck under needle
- improperly adjusted float
- incorrect timing (easier to check though than the first two)
- saturated float
- vacuum leak
- vacuum issue due to removed/plugged lines
- carburetor passages blocked internally somewhere
- incorrect idle mixture
- over pressure fuel pump (mechanical)
Would anyone like to add any thoughts, advice, or additional
troubleshooting steps on my carburetor conundrum?
Thanks,
-Dave
...........
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Jerry & Sharon Work
78 Royale
Kerby, OR
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| Re: [GMCnet] Primary venturis fuel drip at idle [message #333707 is a reply to message #333705] |
Tue, 19 June 2018 16:07  |
Sammy Williams
Messages: 522
Registered: August 2010
Karma: -2
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Senior Member |
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Consider an Edelbrock carb if the one you have now needs a lot of work.
Edelbrocks usually work right out of the box and are usually trouble free.
On the other hand, converting to EFI would be the way to go. After the
almost 1G hit to your bank account and a little labor, you'll have a big
jump in reliability and a small increase in mpg. :)
Sammy Williams
On Tue, Jun 19, 2018 at 3:54 PM Gerald Work wrote:
> Hi Dave,
>
> My suggestion is to save yourself untold frustration by ditching all that
> stuff and install a modern self learning EFI. Your coach
> will drive far more like a modern car.
>
> All gain and no pain except for a one time $1000 hit to your bank account
>
> Jerry
> Jerry Work
> Kerby, OR
> ......:::
> ate: Tue, 19 Jun 2018 14:27:59 -0400
> From: "Dave Stragand"
> To:
> Subject: [GMCnet] Primary venturis fuel drip at idle
> Message-ID:
>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi All,
>
>
>
> I noticed today on my 1978 403 that the primary venturis both have a
> steady splatter/drip of fuel at idle. I would get the same thing
> occasionally on the professionally rebuilt QuadraJet on my '68 Caddy.
> The cause was generally a sticking needle/seat/float - and a quick tap
> or two on the carb from a rubber or plastic mallet would make everything
> peachy again for a few months.
>
>
>
> On my coach I have a quite a few more unknowns, such as:
>
>
>
> - what the timing may currently be set to
>
> - a number of disconnected and plugged vacuum lines
>
> - if the idle mixture is correct
>
> - overall engine condition
>
>
>
> So I was looking for a bit of advice on what the most likely cause(s)
> would be so I can check them in that order. My thoughts are (most
> likely first, least likely last):
>
>
>
> - debris stuck under needle
>
> - improperly adjusted float
>
> - incorrect timing (easier to check though than the first two)
>
> - saturated float
>
> - vacuum leak
>
> - vacuum issue due to removed/plugged lines
>
> - carburetor passages blocked internally somewhere
>
> - incorrect idle mixture
>
> - over pressure fuel pump (mechanical)
>
>
>
> Would anyone like to add any thoughts, advice, or additional
> troubleshooting steps on my carburetor conundrum?
>
>
>
> Thanks,
>
>
>
> -Dave
> ...........
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: [GMCnet] Primary venturis fuel drip at idle [message #333737 is a reply to message #333705] |
Tue, 19 June 2018 22:42 |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
Karma: 5
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Senior Member |
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You're in luck with a 403 engine. You have room to mount
an adapter plate with a square bore carburetor and don't
have to raise the engine hatch cover.
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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| Re: [GMCnet] Primary venturis fuel drip at idle [message #333743 is a reply to message #333737] |
Wed, 20 June 2018 09:31 |
Dave Stragand
Messages: 307
Registered: October 2017
Karma: 0
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Senior Member |
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Thanks to all for the responses. I'll be stopping by today at lunch to
do some checks.
Fred -- I will check the throttle shaft bore by spraying carb cleaner on
the outside base at the shafts while it's running. Thanks for the
reminder as I have run into that before.
I'm leaning towards Bill's suggestion of a timing issue being the cause.
I recall that the rotor shaft was pretty sticky when twisting the rotor,
so I don't fully trust that all is well there. I have a new cap and
rotor so will check the shaft, vacuum advance and advance weights while
I'm in there.
Sammy -- I have had great luck with the Edelbrock (and Carter AFB's)
over the years, but if I was going to change, I would probably lean
towards Gerald's suggestion of EFI. The difference in price would be
well worth it. This is the first time I dragged out a timing light
instead of a laptop to tune a car in many years. It's nice to just turn
the key and go.
While very tempting to pour out upgrade money from the start, I am
holding off on the upgrades until we are sure she has enough 'good
bones' to continue moving forward. At present, the most I have driven
is about 20' backwards and forward -- but when she passes my wife's
"try driving it for 2 hours around the storage facility to make sure
it's in okay shape" test, my wallet will open a bit.
I will keep everyone posted with our progress!
-Dave
1978 Transmode near Pittsburgh
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1978 Transmode (403)
Pittsburgh, PA
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