1972 carb solenoid
Thread Starter
Melting Slicks
Joined: Oct 2010
Posts: 2,276
Likes: 337
From: "ɹǝpunuʍop", Adelaide, South Australia
1972 carb solenoid
on my 350 '72 qudrajet carb, on the drivers side is an electrical solenoid.
no vac line to it, just 1 brown(?) wire.
the bolt in the end dosent touch the throttle linkage at all.
when is / what activates the solenoid?
i thought it might come on when the a/c is turned on, but no.
if i put 12v to it it moves out.
it's just i'm having a strange stalling issue atm.
car idles fine at 900rpm in park, a little rough when moved to netural,
but then the rpm's drop to around 5-600 in drive with foot on brake, and it keeps wanting to stall.
any thoughts?
no vac line to it, just 1 brown(?) wire.
the bolt in the end dosent touch the throttle linkage at all.
when is / what activates the solenoid?
i thought it might come on when the a/c is turned on, but no.
if i put 12v to it it moves out.
it's just i'm having a strange stalling issue atm.
car idles fine at 900rpm in park, a little rough when moved to netural,
but then the rpm's drop to around 5-600 in drive with foot on brake, and it keeps wanting to stall.
any thoughts?
Team Owner
Joined: Sep 2006
Posts: 31,286
Likes: 4,375
From: Westminster Maryland
Hi au,
I believe you're describing the anti-diesel solenoid that was used in 72.
I also believe it was to 'fire' (move the plunger) when the a/c came on in order to increase the idle speed slightly.
Regards,
Alan
I believe you're describing the anti-diesel solenoid that was used in 72.
I also believe it was to 'fire' (move the plunger) when the a/c came on in order to increase the idle speed slightly.
Regards,
Alan
Melting Slicks
Joined: Oct 2006
Posts: 2,417
Likes: 336
From: Texas
"i thought it might come on when the a/c is turned on, but no.
if i put 12v to it it moves out.",
this is how its supposed to work, trace the wire where it ties into ac wiring, should be tied in with the a/c clutch operation. it pushes on carb throttle to keep the rpms up. that bolt on the end of the solenoid will turn and is adjustable.
Alan beat me to it. good luck.
if i put 12v to it it moves out.",
this is how its supposed to work, trace the wire where it ties into ac wiring, should be tied in with the a/c clutch operation. it pushes on carb throttle to keep the rpms up. that bolt on the end of the solenoid will turn and is adjustable.
Alan beat me to it. good luck.
Melting Slicks
Joined: Apr 2010
Posts: 2,315
Likes: 164
From: Broadview hts Ohio
I am not sure that is totally correct. On my 72 non air lt1 it energizes with the ignition on. Then when you turn off the car it de energizes to drop the idle when shutting off engine. May work different with air, but this is how it works non air.
Burning Brakes
Joined: Jan 2009
Posts: 766
Likes: 97
From: Lake Norman, NC
Hmmm. Could Alan and jhudec /BOTH be right? My '72 non-AC car works as jhudec suggests. The solenoid jams against the throttle lever when the ignition is shut off, completely closing the throttle.
Race Director
Joined: Apr 2011
Posts: 11,183
Likes: 3,335
From: North of Toronto - Ontario
72 BB non-AC, Idle stop solenoid is powered with ignition. Idle is set with the solenoid disconnected and then slightly raised with it connected
I believe the function of the solenoid changed from 71 to 72-73 and then again 74+
My understanding on the 72 was to prevent the motor from dropping to a full "low" idle when the throttle was released which may let it actually quit (due to engine braking)
If you try it I believe you'll find there usually isn't actually enough force from the solenoid to push the throttle up, only enough to hold it up once it's there. But if you look at the wiring diagram I don't see any difference in the solenoid between AC and non-AC cars. Only going by the diagram I have though.
M
I believe the function of the solenoid changed from 71 to 72-73 and then again 74+
My understanding on the 72 was to prevent the motor from dropping to a full "low" idle when the throttle was released which may let it actually quit (due to engine braking)
If you try it I believe you'll find there usually isn't actually enough force from the solenoid to push the throttle up, only enough to hold it up once it's there. But if you look at the wiring diagram I don't see any difference in the solenoid between AC and non-AC cars. Only going by the diagram I have though.
M
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
If '72 is the same as '73, which I believe it is, the solenoid gets 12VDC any time the ignition switch is on. It is strictly for anti-dieseling purposes after the ignition is shut off, no other. There is no interaction with the A/C.
The solenoid will force the carb open to the normal hot idle position. Hot idle is adjusted by rotating the hex end of the solenoid piston. Once this is set, the solenoid is unplugged and the idle will drop to a lower speed. This lower speed can be adjusted by rotating a screw against a stop on the carb housing.
The actual speeds can found in the tune up specs.
The solenoid will force the carb open to the normal hot idle position. Hot idle is adjusted by rotating the hex end of the solenoid piston. Once this is set, the solenoid is unplugged and the idle will drop to a lower speed. This lower speed can be adjusted by rotating a screw against a stop on the carb housing.
The actual speeds can found in the tune up specs.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Team Owner
Joined: Sep 2006
Posts: 31,286
Likes: 4,375
From: Westminster Maryland
Hi,
Based on what I've read I think I'm confused?!?
Here's what I THINK..... as soon as the ignition is turned on the solenoid fires.... you can hear the 'click' from the plunger hitting the carb linkage.... but the linkage DOESN'T move.
When the accelerator is depressed to set the choke the solenoid plunger moves a bit further out to increase the idle (not sure why on NON a/c cars, and to help with the compressor load on a/c cars). The plunger stays at that extended position artificially changing the idle speed slightly. The rpm can't drop below the point the plunger is holding the linkage at.
When you turn the ignition off the plunger retracts and the carb linkage is allowed to close the throttle plates completely, helping the engine to not 'diesel'.
The pictures of 72 engines I have access to show the solenoid on all the carbs... sb, bb, with a/c, and without.
Regards,
Alan
Based on what I've read I think I'm confused?!?
Here's what I THINK..... as soon as the ignition is turned on the solenoid fires.... you can hear the 'click' from the plunger hitting the carb linkage.... but the linkage DOESN'T move.
When the accelerator is depressed to set the choke the solenoid plunger moves a bit further out to increase the idle (not sure why on NON a/c cars, and to help with the compressor load on a/c cars). The plunger stays at that extended position artificially changing the idle speed slightly. The rpm can't drop below the point the plunger is holding the linkage at.
When you turn the ignition off the plunger retracts and the carb linkage is allowed to close the throttle plates completely, helping the engine to not 'diesel'.
The pictures of 72 engines I have access to show the solenoid on all the carbs... sb, bb, with a/c, and without.
Regards,
Alan
Last edited by Alan 71; Oct 1, 2013 at 03:51 PM.
Melting Slicks
Joined: Jul 2009
Posts: 3,264
Likes: 3
From: Vero Beach FL
http://api.viglink.com/api/click?for...13806679613998
Burning Brakes
Joined: Jul 2001
Posts: 853
Likes: 0
From: Foxfield, Co
If '72 is the same as '73, which I believe it is, the solenoid gets 12VDC any time the ignition switch is on. It is strictly for anti-dieseling purposes after the ignition is shut off, no other. There is no interaction with the A/C.
The solenoid will force the carb open to the normal hot idle position. Hot idle is adjusted by rotating the hex end of the solenoid piston. Once this is set, the solenoid is unplugged and the idle will drop to a lower speed. This lower speed can be adjusted by rotating a screw against a stop on the carb housing.
The actual speeds can found in the tune up specs.
The solenoid will force the carb open to the normal hot idle position. Hot idle is adjusted by rotating the hex end of the solenoid piston. Once this is set, the solenoid is unplugged and the idle will drop to a lower speed. This lower speed can be adjusted by rotating a screw against a stop on the carb housing.
The actual speeds can found in the tune up specs.