73 LS4 Spark Control Solenoid

[George W.]

I need some help in locating a photo or description of the vacuum connection from the spark control solenoid to the carburetor for a four speed car. The AIM indicates that it is connected somewhere on the back of the carburetor as does Dr. Rebuilds diagram. I cannot determine from these drawings the location of the vacuum source.

I have been able to locate photos of the connection for auto transmission cars but the auto connection is not the same as the four speed. I have not been able to find a usable photo of a four speed car.

Any help in locating this information will be greatly appreciated.

George

[Joe L.]

Re: 73 LS4 Spark Control Solenoid

I need some help in locating a photo or description of the vacuum connection from the spark control solenoid to the carburetor for a four speed car. The AIM indicates that it is connected somewhere on the back of the carburetor as does Dr. Rebuilds diagram. I cannot determine from these drawings the location of the vacuum source.

I have been able to locate photos of the connection for auto transmission cars but the auto connection is not the same as the four speed. I have not been able to find a usable photo of a four speed car.

Any help in locating this information will be greatly appreciated.

George

George-------


If you have or have access to a copy of the "Vette Vues Fact Book of the 73-77 Stingray", there are photos on page 20 of what I believe to be a 1973 LS-4 manual trans solenoid installation.

A word of caution, though: the 1973-77 Fact Book has got to be the worst of Mr. Dobbins' Fact Books. The pictures are HORRIBLE in quality and detail. Important pictures do not appear and photos of "drivel" are everywhere.

[George W.]

Re: 73 LS4 Spark Control Solenoid

Joe

Thank you for your response. I started to purchase that book while in Kissimmee, but put it off until later in the day and forgot it. Unless others supply additional information I will order it.

The carburetor that I have is the correct number 7043201 with the proper date code, but was not on the car when I purchased it. There is a threaded vacuum source at the rear of the carb base that attaches to the power brake booster. About 1" above this connection, in the carburetor body, is a small hole (1/8 to 3/16" diam) that appears to have had a vacuum connection pressed in at some point in time. My guess is that this is where the spark control solenoid is connected. I have test run the engine and there is no vacuum at this source, but I believe it is blocked by the base to body gasket. I plan to disassemble the carburetor this afternoon and see.

George

[Edward J.]

Re: 73 LS4 Spark Control Solenoid

George, that vaccum port may be a ported vaccum supply, which means theres only vaccum under acceleration or part throttle.

I took at look at the doc.s diagram, it looks pretty cut and dry if its a big block car. rear of carb to solonoid then to dist. vaccum advace unit.

[Harmon C.]

Re: 73 LS4 Spark Control Solenoid

I owned a 73 454 4 speed and the TCS solinoid mounts behind the carborator. I looked at the Dr's pictures and it looks like the threaded hole in the base was used or the threaded hole in the intake. I thought my car was hooked to the right front of the carb like 350's.

[Stuart F.]

Re: 73 LS4 Spark Control Solenoid

It stands to reason that any "ported" vacuum source will be at the front of the carb at the primary butterflys. My last experience was with a 72 w/QJ and that was ported at the front. I modified the port chamber with a file, then incorporated a manual switch on the solenoid - all hidden to give me full time vacuum advance for driving and correct operation for emissions testing.

Stu Fox

[George W.]

Re: 73 LS4 Spark Control Solenoid

Thank you all for you responses. I removed the carburetor and found that the smaller vacuum port does connect to the larger threaded port. Installed in the smaller port was a brass plug, preventing a vacuum leak.

I purchased the carburetor in 02 from a reputable individual whose business is locating carburetors for the collector car world and the carburetor was restored by his people. I think this plug was installed at that time, as it is bright brass and does not look as if it was original. I do not know if this port was blocked originally. The carburetor does appear as if this port was used at some time.

I have finished the frame, engine and drive train and have started on the body. I have plenty of time to continue looking for the answer.

George

[Harmon C.]

Re: 73 LS4 Spark Control Solenoid

If your car has power brakes that threaded hole in the base was used as the supply vacuum source. The threaded hole in the intake was used with the automatic tranismission. I have pictures but not in this computer. Some other 73-4 owner may help soon.

[Bill C.]

Re: 73 LS4 Spark Control Solenoid

The ported vacuum source on the 7043200/201 carb is on the DVR side, front by the idle seloniod bracket.

It is used used to "T" into/supply the TCS selonoid, it is mounted (I believe) under the coil bracket (inner).

The top connection goes to the vacuum advance can and the side port receives the signal from the ported source up front.

As for the steel tube which runs alongside the carb (pass side) - I don't know the configuration for a 73.

As for the rear port, it would be for PB as Lyle stated above.

[George W.]

Re: 73 LS4 Spark Control Solenoid

My 73 does have power brakes. The 73 AIM shows the threaded connection at the rear of the carburetor base plate as the vacuum source for the booster and only for the booster. It shows the threaded vacuum source at the rear of the intake as supplying the headlight vac hoses.

The 73 AIM and the 73-74 Technical Information Manual & Judging Guide both indicate that the connection for the spark control solenoid on a LS4 M20/M21 car is at the rear of the carburetor. The M40 connection is to the front of the carburetor at a ported source.

Based on these two technical sources and various vender drawings, I am led to believe that there should be a vacuum source, other than the brake booster, at the rear of the carburetor. As stated earlier my carburetor has this potential source located above the brake booster source.

All thoughts or comments welcome.

George

[Bill C.]

Re: 73 LS4 Spark Control Solenoid

George -

The vac source above the PB port - I thought - was used to control the vacuum modulator for the automatic transmission option. The metal tube from the tranny runs up and directly behind the carb.

Just about every carb I have seen on a Vette with a 4spd has used the front ported source from the factory (for TCS variants).