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Recently I was doing some work to the carb, and I had the yellow plastic part (circled in the image attached) break. What is the name of this part and what does it do for the car? This is my first classic car so I am not super knowledgeable on some systems yet. Obviously it needs to be replaced, but I don't know what to look up to find a replacement. Thanks so much in advance, you all are the best!
Welcome to the boards! I see you have a 72; so do I. Great year for Vettes (All years are!!).
Ratflinger is correct; you car will perform better without that solenoid. Remove it; stuff the two wires and their connector against the firewall; and run your vacuum advance hose directly from the distributor to the vacuum port on your carb.
You mention this is your first classic car. There are a number of tuning tips and techniques that will give you improved performance. Ease into things as you learn and understand them. If you don't already have copies of the 1972 Chevrolet Passenger Car Service Manual and the 1972 Assembly Instruction Manual ('AIM'), you'll really need them. Even a copy of the owner's manual that would have delivered with the car when new. All those references are available from this site's supporting vendors.
Best of luck with your car. Whenever you have questions, ask here. You'll get an answer.
Catfish, for a clear understanding, please define/detail what you mean when you say “you car will perform better without that solenoid.” I don’t know what your “better” involves. Not a swipe, just trying to understand.
This miserable Nixon era device defeats the vacuum advance unless the car is in high gear.....the rest of the time nothing.....not to mention it was plumbed to the ported vacuum port on the carb which did not work at idle.
Deleting it and going to full manifold vacuum restores a nice vacuum "curve" that is dictated by engine demand and not a switch and/or relay....this improves idle, throttle response, fuel efficiency and will lower EGT's.
If you really want it to run good....ask Lars for his timing paper and follow it. You can reach him at V8fastcars@msn.com. Deleting this TCS and putting a real advance curve in as well as proper performance timing settings will make the engine much happier.....and more power. Everybody likes more power right?
The TCS was one of many stopgap ideas to skirt the Gov at the time......most all of theses ideas were pretty terrible, unreliable and some were plain dangerous.
Ha! OK; you got me. I should have just phrased it as “your car will still perform without that solenoid, and as an extra added bonus, your intake manifold will be less cluttered.”
That transmission controlled spark solenoid (TCS) was in place as part of an early emission control system. It allowed no vacuum advance to the distributor at low speed or in low gears (auto or manual trans), and was controlled by a switch on the transmission. It's introduction was only due to the requirement of the 1972 federal exhaust emission restrictions to achieve a decrease in hydrocarbon emissions and oxide of nitrogen emission. Limiting vacuum advance in low speeds and low gears helped meet that goal. Prior to the intrusion of TCS solenoids, distributors had full-time vacuum advance, and cars performed well. Without that solenoid in place, ignition curves could be set to the more performance-oriented specs of prior years.
If a car will be going through NCRS judging, that solenoid will need to be in place or judging points will be lost.
Good, detailed info from both Jebby and Catfish. Thanks guys. I think this detail makes the thread more useful and belongs as part, especially for archiving purposes.
FWIW, I did know but didn't feel I should add interpreted detail to what someone else had offered, and yes, my TCS is on my NCRS car and functions as designed - not that that's a good thing for performance. BTW, I thought I had read also where use of the TCS can raise operating temp in certain conditions. Not sure on that though.
What is this part called?
