[Peter Serio]

You are right about that washer, it's actually a "gasket" to prevent fluid leakage out of the 4 speed.(90 wgt gear oil actually) It's made of copper and it is almost "paper thin", the original GM part # of the gasket was: 3929530. You have to use the gasket as it positions the switch in the right place relative to the trans shift fork lever attachment.


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Peter Serio
Owner, Precision Pontiac

[zedo]

Len,

The TCS system was a primitive emissions device that retarded timing by rendering the vacuum advance inoperable in certain gears and operating temperature.

The bottom line is, for better mileage, power, and driveability, you'd be better off disconnecting it and running a straight vacuum advance. I did comparison tests long ago comparing ported, manifold, and no vacuum advance with street driving. The mileage difference with straight, constant manifold vacuum to the dist. during street driving was very noticeable, around 3 mpg in my car. Mileage would improve from 10 mpg to 13 mpg, with a 400/RA III/3.73 gears.

[jyeager]

I agree with Zeedo. I admire you having a working TCS system. If you desire the pristine show-car then stick with it. For improved drivability and performance hook it to full vacuum. Your only problem when you did this was your idle speed went up. All that requires is a carb adjustment to bring your idle speed back down.

[Leonard Welch]

First - where do you obtain GM part numbers? I ordered a Hollander Interchange manual but returned it because it wasn't as detailed as I need. It wouldn't list part numbers for electrical switches - especialy not the copper washer that you mention!

Second, my car is certainly not 'show'. However, it's a 400 4-speed convertible (1 of 79 - http://www.pontiac.tm/gto/members/19...ardWelch.html) and I'm interested in getting it to run 'as it should'. Then, I can figure out where and what to modify, if necessary.

The reason I got into this in the first place is that the car was running so rich at idle that it was nauseating to ride in - especially with the top up. I first had the carb rebuilt. That didn't do it. Then, I learned how to set the mixture screws. Still nothing. That's when I started to learn about vacuum advance. I discovered that my TCS replacement parts weren't functioning correctly. Many dollars (I purchased 2 NOS vacuum solenoids and 2 transmission switches) later, it works. (Interesting note - I received a National Parts Depot catalog yesterday for Chevelles. The transmission switch is in there for $9! Oh well!)

I've heard recommendations like:

Run ported vacuum directly to the distributor. 1971 4-speed carbs (7041263) don't have a ported vacuum source.

Run manifold vacuum directly to the distributor. This is, in effect, what I had with an inoperable TCS system. The fumes were killing me. When this was ocurring, I did retard the timing a bit but I figured that if I do that, I would be sacrificing performance in 3rd and 4th gear at lower RPMs. True?

Also, if I ran straight manifold vacuum (17 inches at 600 RPMs at 12 degrees BTDC with vacuum advance disconnected) to the distributor, wouldn't my gas mileage decrease since it would cause the car to run richer? Once I would reconnect the vacuum advance, the idle would jump to 800 and the timing looks like it would shoot up another 10 degrees or so.

I do understand that with an operable TCS system, the 1st and 2nd gear performance decreases. I just couldn't figure out a reasonable compromise. The easiest thing would've been connecting to a ported vacuum source - it's just not an option for me.

Ideas? Thanks for listening!

[Carl]

Running rich at idle? Check the float. I always use a brass one. Where is the idle at. Check to see if the throttle plates are past the transfer slot too far. Has the carb been modified? Its possible that the idle tubes have been enlarged. What size jets and rods are you running? It should have a 70 jet,41 rod and a BE secondary rod. What spring is in the power piston? If its too high the rods are beibg pulled up at idle and it will make it run rich. Have the plugs on the bottom of the carb body been epoxied or repaced? If these leak it will make it run rich. FYI you can put a ported vacuum source in that carb also. It just takes time and patience. Set the timing to 12 initial,36 at 25oo and see if it runs rich then. Email me if you want more info.

[Chiefpontiac]

You state that the engine was rebuilt with an HO cam. Do you know which one? I never did get my '69 judge to pass an emissions test with the RAIII Hi Lift (HC-02) installed. The hydrocarbons were sky high at idle due to excessive overlap.

Also, you can modify the carb to add a ported vacuum port. I have done this conversion many times.

BTW: Original jetting for the 7041263 is 75 jets, 46 rods and BU secondary rods.

[Carl]

I was wrong on my first post. According to a GM manual a 7041263 came with 71 jets,43 rods and BU secondary rods.

[Carl]

There are ways to modify the q-jet for a big camshaft. If you are interested email me and I will go over it with you.