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Pontiac of the Month

Pedja's 1968 Firebird

2019 March
of the Month

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Hi,

Wondering if anybody has come across an issue with Quadrajet on 1970 GTO Ram Air?

This carb has no ported vacuum port,only manifold at back of carb.So this would mean if I hook up vac advance from Dizzy it would be vac all the time.

It raises idle,and Im having a hard time getting idle down as it is.

This car also has a TCS solenoid which is where I believe the Vac advance is supposed to be run through,into solenoid from carb then back to dizzy.

Alot of people say that you should run manifold vac and shut down the TCS.

Any thoughts??

Thanks,

Bob H

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I think this is the diagram you're looking for Bob.

image.png.33f20c1cd0525544720e687dd6360e50.png

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Thanks,

Its what I thought, vac source from carb to solenoid then from solenoid to advance on dizzy.

Because of the set up does it mean that advance is only active in 4th gear only as its triggered by switch from trans?

At least thats what I have read.

Bob h

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It means the advance won't get full vacuum to the advance until you are out of 1st and 2nd gear, or if the engine is below 63F or above 263F. The TCS was an early emissions device. You can completely remove it from the system if you want, assuming you are not going for judged points (100 point restoration) or your state does not require emissions testing/original emissions equipment to remain in place and functioning.

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They dont do emissions on classics here in Mass believe it or not.

But on this model carb there  is only constant manifold vac at the back of this quadrajet at the bottom.

So vac advance would be all the time?

Thanks,

Bob

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Correct, you would get full vacuum all the time to the vacuum advance unit by removing the TCS. This would clearly pull your vacuum advance in soon than you are currently use to with the TCS in place. 

 

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Thanks,

Its making more sense.

I was struggling with idle and fuel air mix as I just rebuilt the carb,and I think alot of it was due to vac advance running straight into constant vaccum source.

I also just did pertronix and new distributor,so im timing as well all at the same time.

Trying to get everything in sync is a challenge,found out the hard way the dizzy runs ccw on Pontiac 🤨

 

 

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I have a Pertronix II on my '72 Lemans distributor. I love it - no more points and dwell to worry about. My engine builder had an old Sun distributor curve machine so he could add a lighter spring/weight kit (~$10 from Summit), and re-curve the distributor to bring all the mechanical timing in at a lower RPM.

I find most people who are not (yet) die hard Pontiac aficionados find out the hard way that Pontiac distributors run counter clockwise.

I think your car will like straight and constant vacuum now. Fine tuning a rebuilt carb can sometimes be a pain.

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I think so too,but idle goes way up if I bypass TCS and go direct to constant vac port.

Normal???

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Yes, you will have to change the fast idle screw to adjust the carb so that the revs come back down to normal. Remember, the carb was use to running on partial vacuum, now it is running on full vacuum.

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Yes,

I guess running on full vac is ok,not sure how to do base timing,suppose i could do total timing.

Maybe 40 total at about 3000 rpm not sure as i have been bouncing back and forth with Tcs or not to Tcs.

Thanks,

Bob H

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Initial timing has to be done with the vacuum advance unplugged (but the vacuum source plugged up). 16 degrees of initial timing with around 34-36 degrees of total timing (mechanical and vacuum advance all in) is close to factory spec. Now depending on your cam specs and such, 40 degrees may be okay or it may be too high and you risk denotation. With a near stock cam profile, 40 is pushing it in my opinion. 

 

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Perfect,

Thanks for all your invaluable help

Reg's

Bob H,

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