70 carb, choke rod & stove & vacuum advance line

**Jim T.** · March 14, 2000, 03:09 AM

Re: 70 carb, choke rod &amp; stove &amp; vacuum advance li

As the original owner of a 70 350/300 I am pretty sure that the vacuum tube you mentioned in your post should have a vacuum hose connected to TCS solenoid. The TCS solenoid should be mounted on the intake manifold on the right side of your carb. A vacuum line from the front base of the carb goes to the front nipple on the TCS solenoid. A vacuum line will connect from the horizontal rear nipple of the TCS solenoid to your vacuum advance unit of the distributor. The nipple that is vertical at the rear of the TCS solenoid is where the vacuum hose from the carb will connect. My original carb is off the car and stored in the attic. I removed it in 1973 when I switched to a Holley double pumper spread bore. I will have to look at my original choke rod later this morning to check its length. One of the first modifications I did to my 70 was hook up vacuum advance full time from the carb to the vacuum advance unit. This gave a immediate increase in gas milage in city driving.

**Juliet P.** · March 14, 2000, 09:25 AM

Should I have TCS? Early (no AIR) 350/300 Auto.

Jim, Out of curiousity, what number is your '70? Mine's an early one #4102 build date Feb 18, '70. At the moment there is ZERO emissions stuff on the car. It has the '69 style air cleaner assembly (larger diameter, no snorkels, open element). By TCS do you mean Transmission Control Spark solenoid? Is that part of the AIR system or is that something I should have even without the AIR? Those of you familiar with this PLEASE chime in with info. :-)

I didn't think that the base engine '70 (non-calif car) had an AIR system. Does it matter if it's Auto / 4-spd? I have a TH400 trans. Oh gee, I'm wondering now if there's stuff missing here... There was a really convenient stud (too convenient) on the intake manifold on the passenger side where I attached the vacuum line clip (which was missing). I suppose that's where it's supposed to be if I should have one that is. Anyone have any pictures? The JM shows the other side of the carb & AIR system, not the TCS solenoid.

I'm off to the catalogs to see if these things can be purchased... and how much it's gonna cost me... if indeed I should have one! Ack, what's it going to do to performance?

Thanks. I'll be eagerly awaiting some replies on the subject. Though, ignorance WAS bliss! ~Juliet

Juliet's 1970 Corvette

**Jim T.** · March 14, 2000, 11:49 AM

Re: Should I have TCS? Early (no AIR) 350/300 Auto

I have an late 70 model coupe #414654.TCS does mean transmission controlled spark. From the pictures in my revised second edition Vette Vues Fact Book for 68-72 Stringray by M.F. Dobbins I can report that the base engine 350/300, 350/350 HP and even the 350/370 HP engines all used the TCS solenoid. The base 350/300 and the 350/350 engines did not use the AIR system. The LT-1 350/370 did use the AIR system. Also I observed that the base engine, yours and mine should have the fresh air vacuum hose connected to an outlet on the side of the carb. Looking at my original carb removed in 1973 I now stand corrected in that my previous post mentioned that it was at the rear. This fresh air outlet hose to the solenoid comes out of the carb right under the linkage for the vacuum operated choke pull off system. In the fact book they show the fresh air tube on the 350/350 carb attaching to the rear of the carb. The TCS solenoid mounts to a manifold stud in the cavity of the intake manifold just behind the intake maniford mounted choke spring assembly. Both the turbo 400s and the 4-speeds used the TCS solenoid. More than just Corvettes used the TCS solenoid. If you have some salvage yards you don't mind visiting you can go and look for 69-70-71 GM cars out in the lot if they have the engines in them and look on their racks for pulled complete engines with the TCS solenoid still mounted. Good luck.

**Joe L.** · March 14, 2000, 12:51 PM

Re: 70 carb, choke rod &amp; stove &amp; vacuum advance li

Juliet-----

You won't be able to use the LT-1 choke rod on your QJet-equipped 70. The Holley choke rod is a completely different configuration and the Holley choke thermostat operates in an "opposite direction" from the QJet style. There were, in fact, two different choke rods used for 1970 Corvette 350/300 engines, depending upon whether or not the car was originally a California-delivered car with the NA9 emissions package. This package included the evaporative emissions control system(EEC). Cars so-equipped can be identified by the charcoal cannister mounted under the hood in the left rear fender well area and the insulators found in the carb air horn assembly on the carb-to-manifold forward mounting bolts. NA9 cars WERE NOT equipped with A.I.R. as some folks think; ALL 1970 Corvettes, except LT-1, used the "controlled combustion system"(CCS) exhaust emissions control system.

The choke thermostat which you require is GM #3973497. This piece is GM-discontinued but easily available from "reproduction" sources. It is also usually available from auto parts stores as manufactured by Echlin, Napa, Standard Motor Parts, Filko, and others. These aftermarket pieces are virtually IDENTICAL in every way to the originals. Your local auto parts man ought to be able to cros-reference the correct part from the above GM part number if all else fails.

The original auto choke rod for your car was GM #3970080 if your car is a non-NA9 car which is the most likely scenario. If an NA9 car, it was GM #3970084. Both are discontinued, but the latter one(which you probably don't need)is, by far, the hardest to find and it is not reproduced. However, the 70 NON-NA9 choke rod, which is what you probably require, IS available in reproduction. Dr. Rebuild carries it under his part number 3752324 for $10. Other Corvette suppliers probably have it,too. For the above referenced choke rods to work properly, however, you MUST use an original, or equivalent to original, 1970 carb base gasket. This gasket, GM #3967470, is NOT a thick insulating type gasket. It is GM-discontinued but available in reproduction from Dr. Rebuild and many others. You can also probably get it at your local auto parts store. The THICK INSULATING gasket, GM #3969837(currently GM #10147945)was used only on NA-9 equipped cars for 1970. If you use this gasket, you cannot use the stock choke rod and will have to fabricate one from .125" rod.

Your choke thermostat cover is GM #3864866 and is still available from GM under that part number for a nominal cost.

Your carburetor throttle body assembly(the part that mates to the manifold surface) is a machined, cast aluminum part. It is usually NOT colored as is the float bowl and air horn assemblies.

As far as I know, all 1970 Corvettes used the transmission controlled spark system (TCS) whether automatic or manual trans equipped or whether or not NA9 equipped. This system essentially consisted of a transmission switch, relay, solenoid valve, temp switch(right rear cylinder head), and associated wiring/vacuum lines. For your car, the only part of the system which MAY still be available from GM is the relay which was unique to 70 model Chevrolet cars. This relay is GM #3961573. All other parts are discontinued although, if your car is a manual trans car, the transmission switch is also still available(GM #3961567)

**dennis** · March 14, 2000, 02:21 PM

Jim Trekell

I'm curious what, if any adjustments (timing/carb)you made after you went direct for your vac. source.

**Joe L.** · March 14, 2000, 03:42 PM

Re: 70 carb, choke rod &amp; stove &amp; vacuum advance li

Juliet-----

The following are the major parts you need to rebuild your 1970 TCS system, if you choose to do so:

GM #1114432----SOLENOID---discontinued but The Last Detail in Atlanta, GA might be able to supply you with one. Otherwise, contact M&H Electrical Fabricators of Santa Fe Sporings, CA.

GM #6489785----TEMP SENSOR---discontinued; available from Dr. Rebuild and others

GM #3961573----RELAY; still available

GM #6462286----SWITCH, trans mounted with THM400----discontinued but may still be on your trans.

OR

GM #3961567----SWITCH, trans mounted with manual trans----still available.

**Sal C.** · March 14, 2000, 05:46 PM

Re: Should I have TCS? Early (no AIR) 350/300 Auto

All 1970s had a TCS solenoid. The part number is 1114432 for the small block and is stamped on the bracket portion of the assembly. There is a drawing devated to this and the choke assembly on page K194 of the 1970 assembly manual. This part has long been discontinued by GM.

**Juliet P.** · March 14, 2000, 07:05 PM

Re: 70 carb, choke rod &amp; stove &amp; vacuum advance li

Well RATS, RATS and Double DRATS! I'm supposed to have one of these TCS beasts. It would appear that when the prior owner replaced the original carb with a '69 carb (without the extra vacuum port) she let the mechanic remove the TCS solenoid. I thought that the studded manifold bolt was too convenient for the vacuum line clip. But that also explains the mish mash of a vacuum advance lines cobbled together. With the TCS solenoid location the vac adv steel portion of the line I do have is probably the original one. It appears to be the appropriate length to go to where the TCS should be.

Fortunately I do have the green wires & temp sensor in the block and there is a relay near the vacuum pump where the wires connect. I haven't jacked the car up yet to check the trans for the other components which are supposed to be down there yet, but from my flashlight & mirror I think there are wires going in that direction.....

Gee, just goes to show me what I do / don't have! I'm sure Sunday's NCRS judging at Glen Burnie will be equally eye-opening! ... though I hope there aren't too many other big surprises in store for me! ~Juliet

Juliet's 1970 Corvette

**Roberto L.** · March 14, 2000, 07:08 PM

Re: 70 carb, choke rod &amp; stove &amp; vacuum advance li

In the link below there is a photo of firewall in my 70 (manual), showing some components dissasembled and TCS relay which reads Littlefuse Inc, #3961573 as Joe explained. It uses 5/16 screws with oblong reinforcement. Uncle Jack teached me that there is a date in the cover (tiny). As others said all 70 cars have TCS system. Hope this helps Roberto, NCRS #30019, RMC

70 TCS relay in firewall

**Juliet P.** · March 14, 2000, 07:18 PM

Forgot to Mention about AIM drawing...

I've located the diagram in the AIM, however the revision record indicates that the solenoid drawing was revised in 3-6-70. I guess in my mind I was wishing / hoping that this was one of those early late things... and it wasn't added until late march, as indicated in the revision date... especially since my car has so many 1969 parts on it. On the bright side of things, at least I might still have the original vacuum advance line!

Thanks for all the information & part numbers. It looks like the major missing component is the TCS solenoid... hopefully that's all. And for missing vette parts on 1970s this one (at around $100) is Cheap! :) Thanks, Juliet

Juliet's 1970 Corvette

**Joe L.** · March 14, 2000, 07:32 PM

Re: Forgot to Mention about AIM drawing...

Juliet-----

Keep in mind that replacement of the TCS system is an ORIGINALITY ISSUE ONLY; it is NOT A FUNCTIONAL ISSUE, except in locations which would consider its removal an emissions violation. FUNCTIONALLY, your car will perform better using direct vacuum to the distributor vacuum control and distributor advance characteristics modified to mimic the 1969 300/350 configuration.

**Roberto L.** · March 14, 2000, 07:34 PM

Re: 70 carb, choke rod &amp; stove &amp; vacuum advance li

For California 70 cars with NA9, I have gasket and aluminum heat shield photo in the link below, just for reference. Roberto, NCRS #30019, RMC

70 NA9 gasket and alum heat shield

**Jack H.** · March 14, 2000, 07:42 PM

As Roberto said....

TCS solenoid and control relay are common to ALL Chevy passenger cars of the era. UJ simply strolls the local 'bone yards', grabs the good looking, properly date coded, used parts and takes 'em for a swim in his Eastwood's home plating tank (being careful with relays not to let acid penetrate) and wham, bam, you're done for a whooping $3....

**Robert C.** · March 14, 2000, 07:52 PM

Re: You got one?

Glad to see your name on the board, Sal. Hear you've been down awhile.Hope you are OK now. I bet you got one of those TCS's for the post gal. Later, Bob

70 carb, choke rod & stove & vacuum advance line