Rochester Carb Question
Thread Starter
Heel & Toe
Joined: Aug 2013
Posts: 19
Likes: 0
Rochester Carb Question
This likely seems like a pretty lame question to senior members and those in the know... but here goes.
What is the purpose of the canister that sits immediately forward of the throttle linkage at the carburetor on my 1977 350. It has a single wire running to it and looks like it gets actuated by the linkage.. or vice versa.
How do I determine if it is functional.
Thanks guys.
What is the purpose of the canister that sits immediately forward of the throttle linkage at the carburetor on my 1977 350. It has a single wire running to it and looks like it gets actuated by the linkage.. or vice versa.
How do I determine if it is functional.
Thanks guys.
Last edited by 1977C34ME; Dec 5, 2013 at 08:25 AM. Reason: claricication
Le Mans Master
Joined: Feb 1999
Posts: 8,351
Likes: 75
From: Tampa Bay FL
On my '80 L48, this device, an 'Idle Stop Solenoid', presses against the throttle blade when the A/C is running; to compensate for the drag on the engine.
On eBay for your '78 vette:
http://www.ebay.com/itm/Auto-Tune-A4...92d424&vxp=mtr
I stand corrected. Found the following comment on a BBS:
"It's an anti-dieseling solenoid not a idle control solenoid for the hvac.
Back in ancient times, retarded spark and lean air/fuel ratios to reduce emissions meant a lot of curb idle throttle opening to maintain idle speed. Problem was, when you'd shut the engine down, it would tend to "run-on" or "diesel". That solenoid exists to fully close the throttle plates upon shutdown. "
I've improved my timing and ignition and rarely if ever see this item activated on my '80 L48.
On eBay for your '78 vette:
http://www.ebay.com/itm/Auto-Tune-A4...92d424&vxp=mtr
I stand corrected. Found the following comment on a BBS:
"It's an anti-dieseling solenoid not a idle control solenoid for the hvac.
Back in ancient times, retarded spark and lean air/fuel ratios to reduce emissions meant a lot of curb idle throttle opening to maintain idle speed. Problem was, when you'd shut the engine down, it would tend to "run-on" or "diesel". That solenoid exists to fully close the throttle plates upon shutdown. "
I've improved my timing and ignition and rarely if ever see this item activated on my '80 L48.
Last edited by TedH; Dec 5, 2013 at 08:36 AM.
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
Actually, the solenoid prevents dieseling. For proper idle speed on A/C cars, the carb's primaries have to be open too much which uncovers the transfer slots which allows fuel to be pulled into the induction system after the ignition is turned off, which often causes dieseling.
So in about 1971, GM took the ordinary idle adjustment out play and deployed this solenoid instead. The plunger is extended when the engine is running. When the ignition is shut off the plunger is quickly pulled back allowing the primaries to close completely preventing fuel from entering the hot combustion chambers. (Make sure the set screw for the idle speed at the throttle linkage is out of play).
You're also to adjust the idle speed using a 1/2 wrench on the hex of the plunger.
So in about 1971, GM took the ordinary idle adjustment out play and deployed this solenoid instead. The plunger is extended when the engine is running. When the ignition is shut off the plunger is quickly pulled back allowing the primaries to close completely preventing fuel from entering the hot combustion chambers. (Make sure the set screw for the idle speed at the throttle linkage is out of play).
You're also to adjust the idle speed using a 1/2 wrench on the hex of the plunger.
Last edited by 73, Dark Blue 454; Dec 6, 2013 at 12:55 AM.
Drifting
Joined: Mar 2011
Posts: 1,886
Likes: 9
Once you have modified your distributor to operate on full time vacuum advance, the tendency for the engine to run-on is very much reduced.
Then, you can wire the solonoid to keep the idle speed up when the air conditioner compressor is engaged. (Not NCRS correct, but useful)
Then, you can wire the solonoid to keep the idle speed up when the air conditioner compressor is engaged. (Not NCRS correct, but useful)
