| [GMCnet] Primary venturis fuel drip at idle [message #333699] |
Tue, 19 June 2018 13:27  |
Dave Stragand
Messages: 307
Registered: October 2017
Karma: 0
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Senior Member |
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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
1978 Transmode near Pittsburgh, who thinks EFI is looking better and
better. =)
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1978 Transmode (403)
Pittsburgh, PA
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| Re: [GMCnet] Primary venturis fuel drip at idle [message #333700 is a reply to message #333699] |
Tue, 19 June 2018 14:20  |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
Karma: 5
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Senior Member |
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Hello Dave,
My quadrajet did the same thing.
I found that my timing was retarded and the idle adjustment was set to open
the throttle, to get my RPM higher. After getting the ignition timing corrected,
advancing it to 8 degrees, I could adjust the idle speed back down.
And the fuel drip from the venturies stopped.
If you take the carburetor off and look at the throttle plate, there's a transition
slot which allows vacuum to pull fuel from the bowl, when you start opening the throttle
slightly above idle. The slot should be barely visible with the idle speed set correctly.
If too much of the slot is showing at idle, vacuum can start fuel flow before it's needed.
Regards,
Bill
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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