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Find answers to Frequently Asked Questions for First Generation Firebirds that have been asked on First Generation Firebird-L mailing list. Special thanks needs to be given to all the Firebird-L owners that took the time to respond to other subscribers questions. These pages are continuously updated as new information is posted on the mailing list.
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| Q: | '68 Changing to a 4 barrel Carb |
| When changing from a stock 2 barrel setup, to a 4 barrel, what parts are need to be changed, and what donor years are ok. The car is a 68 350 automatic, and I have a freshly rebuilt Q jet. | |
| A: |
It's not a difficult swap, but there are a few gotchyas to
look out for.
-Spreadbore intake castings are pretty much the same from 1968 thru 1972. In 1973, Pontiac started using an EGR valve, and in 1976 or 1977, the intake was redesigned with more restritive ports. Thes are identified with an odd waffle imprint on the rear of the intake, behind the carb flange. These characteristics make these later intakes less desireable. Some 4bbl. intakes before 1968 were for squarebore carbs (using Carter AFB carbs), and the 1967 Qjet intake has an odd heat passage on the carb flange. -Throttle cables and cable brackets differ from 2 bbl. and 4 bbl. applications. You will find that your 2 bbl. cable will not give you a full range of motion and may require some fabrication to get full throttle. Reproduction 4 bbl. cables are now available from Performance Years. You'll have to hunt the scrap yards for the bracket, or modify yours. (Need link to modify instructions) -More on throttle brackets. Pontiac used a rod for 1967 cars, and then went to a cable for the 1968 and later cars. This cable is very different from that used in later Chevy applications. Around 1970 or 1971, the cable and bracket design changed again, eventually evolving to be more like the Chevy design. So, beware of cables or brackets from earlier or later cars (you don't indicate what year your car is). -You'll need a 4bbl. aircleaner. If you insist on a stock look, try First Generation Firebird's, ebay's, Classical Pontiac's classified pages. |
| Q: | '67 Models of Rochester Quadrajet Carbs |
| I was wondering if my car should have a Q-jet or not. I have a 67 Firebird 400 convertible I'm trying to get back to original condition. Does anyone know what carb and number was stock? | |
| A: |
Here are the five different models of Rochester Quadrajet carbs used on
1967 Firebirds with a 400 cid engine:
7027272 .................. 400 cu.in. A.T. 7027273 .................. 400 cu.in. M.T. 7037272 ........ 400 cu.in. A.T. w-A.I.R. 7037273 ........ 400 cu.in. M.T. Ram-Air* 7037276 ........ 400 cu.in. A.T. Ram-Air* * With or Without A.I.R |
| Q: | '68 Rochester 4bbl Carburator |
| I have a chance to buy a Rochester 4bbl carburator for my '68 H.O. How much is this worth since it is already up to $200 on eBay? | |
| A: |
The 7028269 Rochester 4Bbl Carb was originally used on
all 1968 Tempest and Firebird 350, Manual Trans, 4Bbl engines.
According to the PMD Engine Production Log Records: 2,658 "WR" code (Tempest) 350 HO 4Bbl, M.T. engines were built. 3,784 "WK" code (Firebird) 350 HO 4Bbl, M.T. engines were built. So, there were 6,442 engines built that year using the # 7028269 Carb. Additionally, there were Service Replacement Carbs. mfg. with this same number. (though sometimes found with date codes 1-3yrs. past production.) Not sure where the seller came up with the production number of 1,400 and that all carbs were built on the same day. I'd have to see documented evidence before believing that one. Carbs. were generally built to spec. according to build orders unless the carb was some odd-ball, low production unit such as RAV. Speaking of Date Codes, some early production '68 model Rochester Carbs did not have a date code. Others were stamped on the LH, Rear edge of the Throttle Body (lower section). Most date codes were stamped on the Bowl Assy. near the Rochester Assy Number. Date Codes used the Julian Date System. (day of year- 3 digits followed by last digit of year)... 245 8 (245th day of '68, '78). If your Firebird is documented as a 350 HO car and you would like to have all the numbers match, you might want to pick this carb up. I wouldn't get too carried away in the bidding war... this is not a "rare" carb. Considering a good rebuild can cost upwards of $300+, I wouldn't spend over $200 on the carb as it is. Of course, if you're a numbers nut like me, money sometimes isn't the primary issue. Best advice: wait and bid just before the end of the auction. |
| Q: | Quadrajet Carb Problem |
|
I have a 68 Firebird 400 with a Quadrajet carb. The engine is idling to high
(1000 RPM or so in drive) when warm with the choke open. The idle adjust
screw is backed all the way out and the mixture screws are adjusted. No
detectable vacuum leaks and the throttle linkage is loose at idle. The only
modification is an open element air cleaner.
Any ideas as to why the car is idling high? If you think I need a rebuild, any suggestions for my daily driver? | |
| A: | Check the SECONDARIES .... these are always overlooked ... and should be closed under an idle condition. If this isnt it then check the set screw that adjusts the butterflies. |
| A: | I'd bet the problem lies in the orientation of your throttle linkage, throttle cable, or throttle cable bracket. Pull the keeper pin that holds the cable to the throttle linkage. Let the linkage relax to the closed position. Pull the cable all the way out with your fingers and hold it next to the point where it hooks to the linkage. My guess is that you will need to shift things around a bit to get the eye hole in the end of the cable to reach the throttle linkage connection point in its closed position. |
| A: | I just hadthe same problem with mine .. I ended up looking at the petal itself , over the years it has been hit so many times that it was bent ...{ my lead foot }... so it stayed about 1200 rpm ... I had to rebend the petal to set it right |
| A: | Did the problem happen all at once?If so is the choke step coming off all the way?This type of setup likes to bind.A little wd 40 or liquid wrench will solve the problem.My Bird stays parked alot so the linkage will bind and a quick shot with the spray and away I go |
| A: |
I've had that happen and the secondaries staying open were the problem as pointed out earlier. Another guess....Could it also be that the float needle is
not seating, or might be worn out???
Is it possible that you did something out of the ordinary that might have caused the problem? Perhaps dropped a tool on the carb while working on your car and bent some carb linkage? Another thought.... Is there a slow idle solenoid on the carb? Is it stuck? My last shot at it.... You may have gotten to close to a Rice Burner and sucked it into the carb. No big deal. Just push it all the way in.. Your bird loves seed! |
| A: | It's either a vacuum leak or ignition timing. check your timing and make sure it's at it's proper setting. To check for vacuum leaks, unplug one vacuum line (from the carb) at a time and plug the port. If the idle is unchanged reattach the line and move to the next line. After you've verified that the lines and their accessories are working properly, take some WD-40 and spray it on the throttle shaft on the bottom plate of the carb. Next move to the carb gasket and spray all around it. Lastly, spray the intake manifold around the intake ports at the heads. |
| A: | i would bet the front butterflies are not closing properly if so you might have some build up in the bores of your carb. look into the bores with a flashlight and see if you see any build up that sort of looks like water scale where the butterflies touch the bores when closed i hade this problem before you might can clean it but would be better with a rebuild |
| Q: | Gasket between Qjet and intake |
|
While spraying Gummout carb cleaner down the primaries on my Quadrajet carb on my '68 400, I noticed that the
Gummout was leaking out from between the Qjet and the intake. Not a good
sign. I assume that is my problem (or I created the problem with too much
Gummout carb cleaner).
Here are my questions: Should I use gasket sealer on the new gasket or should it go on without and sealer? Do I need a torque wrench for the bolts? | |
| A: | This may or may not be a fix, but .........when I got mine OHC running it was missing out a little. Then it was suggested that there was a thin metal gasket that should go between the bottom of the carb and the intake. I went to a speed shop and got a thin gasket ( it was just a thin piece of sheet metal with the 4 holes in it ) and voila, I have not had any problems since. Apparently it always had one on it and when I took the car apart I either lost it or chunked it. I think it cost about $5 and was in stock hanging on the wall at a performance shop. May be worth a shot. |
| A: | This same gasket is needed on '67 Qjet intakes as well. There's a heat passage along the intake in front of where the carb sits. I know, I learned this one the hard way! |
| Q: | Carter Carburetor Adjustments |
| The carter carb is very similiar if not almost identical to an edelbrock 600 cfm carb. I really need assistance and desperately. One of the questions is about the two screws on the front of the carb at the base. What should these screws be turned to? The carb has an electric choke and how should this be set? And would there be any other adjustments that I could do to it? I seem to be getting much poorer fuel mileage that the stock carter carb that was on the 326. I bought this new carb thinking I would increase mileage but has turned just the opposite!! This could be because I do not have it adjusted right. I really would appreciate any help that someone can give. Thanks. | |
| A: |
The two screws on the front are the idle mixture screws turning them out (counter-clockwise) will richen the mixture & vice versa.They have
no effect on the mixture at cruise(in otherwards if its too rich at driving
speeds adjusting these will not help) as for setting them,the only real
"correct way" is with an exhaust gas analyzer.Setting with a vacuum guage
may work but likely the smoothest idle will be too rich if your state does
emission testing.Having said that
try turning the screws in one at a time (with the engine off) & counting
the number of turns on each(In a perfect world they should be the same)
then back them both out to the smaller number of turns.Now restart the car
(which should have been already warmed up).Now try turning both of the
screws 1/2 a turn in,if the car starts running rougher you are too lean (&
you should back the screws out again & try going out in 1/2 turn increments
until you find it makes no further improvement then go back in 1/2 a turn
or so),if the idle improves try another 1/2 turn until you find where it
starts to run rough then back the screws out 1/2 turn or so.Basically you
are trying for the smoothest idle & then (slightly) leaning the mixture.
As for the choke setting,basically you want the choke valve to just close on a long cool off (sitting overnight or a number of hours) this is assuming that the weather is mild (so when it is really cold it will be closed with more tension).The plate should be open completely after approx 5 minutes running time no more than 10 anyhow. I hope this helps.. |
| Q: | Adjusting Idle Fuel Mixture |
| The idle fuel mixture seems to be too rich. I have fiddled with the two idle screws on the bottom of the Q-Jet carb but it still runs too fat. Stinks up the neighborhood. Is there a systomatic way of trying to lean out the idle rather than me just turning screws. | |
| A: | The mixture screws are the only control for idle fuel mixture.The carb's main jets control the mixture the rest off the time.The idle circuit is metered through the main jets,then through some calibrated restrictions which are difficult to modify. Changing the main jets will have no measurable effect on the idle mixture.I have found though,that sometimes people think the mixture is too rich when they smell unburned fuel coming out the exhaust and the problem is actually that it's too lean causing poor idling/misfiring and the unburned fuel smell is from the misfiring.Obviously you want to check for vacuum leaks,timing,dwell (if you have points) etc.Lastly,a high mileage engine may emit a lot of unburned fuel from lack of cylinder sealing even though it seems to run well.Just some food for thought. |
| Q: | '67 Stock Carburetor Application |
| Can anyone tell me once and for all what carb came stock on a 67 firebird 400? I have a lot of conflicting information on weather a Rochester quadrajet or a Carter AFB. | |
| A: | For '67 Firebirds...only the 326 H.O. used the Carter Carb. All other applications used the Rochester. |
| Q: | Carburetor - Converting From 2 BBl to 4BBL |
|
I'm converting my '68 2 BBL to a 4 BBL EDELBROCK Performer 600. I'm up to the point of making connections to the carb (linkage, fuel line, air cleaner, vacuum lines). I have the following questions (I know several of you have done this).
Note: Bare in mind that the article in the Jan.99 issue of Car Craft covers a 4bbl Qjet to 4bbl Edelbrock swap. The article is a little lean on details in any case. 1. The carb didn't come with any linkage parts or documentation (I bought it used). The original accelerator cable doesn't reach the throttle points on the carb using the stock bracket. Any suggestions on how to hook this up? 2. The fuel line originally bolts to the front of the stock carb. Now it "routes" to the right side of the carb. and requires an inline fuel filter. I bought a Specter glass filter. Are there any kits for hooking up to the stock line or do I need to make my own. 3. I also installed the Edelbrock Performer intake. What's the best point for connecting the vacuum advanced and PVC valve (do I even need a PVC valve)? On the 2 BBL setup, there was vacuum point on the intake connected to a port below the throttle butterfly. Is it still needed? 4. The stock air cleaner had an air breather tube connector to the top of the right valve cover. Is this still needed, or can I cap it off. 5. What do I do with the large ports at the top of the Edelbrock carb. Do I cap them off? | |
| A: |
Q1: You will need to get an aftermarket bracket. It will bring the cable closer to the throttle lever on your carb. The Edelbrock catalog shows a number of linkage accessories that might be helpful.
http://www.edelbrock.com/ You may need to fabricate something for your kickdown switch. Maybe using parts from your 2bbl carb. Q2: Edelbrock has a fuel line kit (#8135) that consists of a rubber hose, some fittings,a filter, and clamps. In addition, you will most likely need a banjo fitting (#8089) to allow clearance for a low profile air cleaner. There are no hard line kits. You will have to make your own hard lines if desired. Tube bending and flairing can be fun! If you use a rubber line, route it away from heat sources to avoid percolating you fuel, or fire danger. Q3: If the manifold does not have a vacuum fitting, then there are three provisions on the carb for vacuum. Looking at the carb from the front, there is a large port in the center of the base. This is your PCV port. This is critical to keep crankcase pressure under control so that you don't get oil blowby at the rings. To the right of this is a smaller fitting. This is a full time vacuum port. To the left (I think) is a ported (part time) vacuum port. Most distributors use this port but you must verify that this is the type of vacuum needed by you. Cap off the unused port so that you won't have a vacuum leak. Q4: 2 options. Get rid of the tube and put a breather on the valve cover opening. Or knock out the plug at the bottom of the aftermarket air cleaner, get a fitting (from any performance section of your parts store) for the hose and route it there. If you use a stock (4bbl) air cleaner, then use the hose as in stock configuration. Q5: I can't recall their function. I'll check my user manual. You might also contact Edelbrock on this. |
| A: | Any 4bbl air cleaner will work as long as the carb neck is the same (most are universal). Look for one that the intake neck is on the same side as your current cleaner. Look at a second gen firebird, should be close. be careful the one you pick isn't too tall. Compare with the original and if taller, close hood SLOWLY to be safe. If you chose well, most people will not have a clue it's not original. This would get you by until you can find an original. |
| Q: | Kick Down Switch |
| Where did you get this switch? I'll have to double check, but I'm almost positive that mine is missing... and will need that with my 455! Just wondering where I can find it? | |
| A: |
The part is by BandM, Summit part no. BMM-20297. It's listed on page 159
of Summit's catalog that was good through June 30, but you'll have to
check the web for a picture. Just search with that part number at
http://www.summitracing.com.
The kit is intended to be used with an existing TH350 bracket when you swap in a TH400. I already had a TH400 and no bracket at all, so I had to fab a mounting bracket and a small piece to attach it to the throttle. Not tough if you're handy with tools. The linkage is adjustable and very forgiving for differences in mounting methods. |
| Q: | Throttle Kickdown Switch for '68 |
| Can someone provide me with the GM part number for the kickdown switch for a 68 coupe 400/TH400? | |
| A: |
the part number for the kickdown switch is:
#9785545 (same.... 65-66 P/8 M-40, 67-69 F/8 M-40) |
| Q: | Throttle and Kickdown Hookup for '69 |
| Anyone happen to have a picture of how the throttle and kickdown cables hookup to the bracket and the Carb Lever for a '69 4bbl with TH350? How about a good description? I'm pretty sure I have the throttle cable right but I'm not quite sure how the TH350 kickdown cable hooks up. | |
| A: | The kickdown cable snaps into a square hole on the carburetor side of the throttle bracket. If you don't have the exact bracket you will have to improvise. A 2bbl one will not work, the cable will be 3/4" short of the carburetor bracket. The reproduced ones for $80+ are for '68 and don't have the necessary square hole for a TH350. If you find a source for a four barrel cable mounted throttle bracket with the TH350 kickdown hole, let me know. |
| Q: | '68/'69 Firebird Throttle Cables |
| I need help finding a throttle cable for a "68 400. What one is correct? | |
| A: |
Well, it seems there are some out there selling NOS cables as
something they are not.
INFO I'VE DISCOVERED (*thanks to all who've shared*) ORIG. GM PART NUMBERS: 9792222 68/69 F-6 1Bbl, F-8 2Bbl ***YELLOW TAG*** Total Length End-to-End: 19.5" Case Length: 13.5" (((This one is apparently still avail. from GM for approx. $25))) 9792223 68/69 F-6 4Bbl ***BLUE TAG*** 9792224 68/69 F-8 4Bbl ***WHITE TAG*** Total Length End-to-End: 18.0" Case Length: 12.5"Now, in order to confirm all of this, it would be nice if any owner's could measure their cables/cases. This includes all of the above... 4Bbl V-8, 2Bbl, 1Bbl I have a few pictures that I'm trying to get on the Generation-1 WebSite for comparison but AOL has been a real annoyance lately in updating info. Anyhow, if the updates come through, they'll be at the following site: http://members.aol.com/Framair/TechTips.html Thanks again to all who've helped out on this one. Sharing this sorta information will help to educate all of us (me included) on 'Bird Parts. |
| Q: | '69 Throttle Cable Bracket Codes |
| I just bought that bracket off eBay and think it may be the wrong one. It appears to have an F2 on it and someone told me he thinks the 69 firebird 4 bbls have an F4 on em. Is there a difference for automatic or sticks? | |
| A: |
The Throttle Cable Bracket fromE-Bay Auction is for
a '69 Firebird 2Bbl application. The "F2" designates 2bbl.
The correct Bracket for a '69 Firebird 4Bbl is 9797415 which is stamped
with "F4" (for 4Bbl).
Since we're on the subject, sometime in May of '68, a new Intake Manifold and Throttle Cable Bracket for the 4Bbl Firebird came into production. Intake manifold: 9794234 Throttle Cable Bracket: 9797415 (F4) This Manifold was used on late model '68 Firebirds, GTOs, Full Size models with 4bbl Carbs. Also used on all '69 models with 4Bbl. This set-up superseded the previous manifold/bracket... '68 Firebird (1st Type up until May of '68) Intake Manifold: 9790140 Throttle Cable Bracket: 9792242 I believe that the Throttle Cable Bracket you're looking for has been reproduced. There is no difference in Throttle Cable Brackets for Auto/Man Trans. |
| Q: | Throttle Cable Bracket Replacement |
| I am changing out the intake manifold and the carb on my 68 bird and it seems that the throttle bracket would have to be replaced. The intake is an Edlebrock Performer and the carb is an Edlebrock 600 cfm non egr carb... the stock carb is a 2bbl. i wanted to know if anyone has fit one of these carbs on their bird, and what kind of throttle bracket they used. The stock bracket seems to short. | |
| A: |
I just did the exact same thing. I installed the Edelbrock Pontiac Performer
and the Edelbrock 600cfm carb.
I did not have the old original throttle bracket to begin with; just some
old homemade bracket that was used on the Holley carb previously on there.
The Holley throttle linkage sat much lower and I could not reuse the
"homemade" bracket with the new Edelbrock carb.
What Edelbrock tech support says to do (after I was on hold for 15 minutes) is not quite the right thing to do. They say you need to purchase their Throttle Bracket--Pontiac ('68-'71) P/N #8015 . When you order this and get this, it has instructions telling you how to modify your old original throttle bracket!! Drill here, bend here....NONSENSE! It looks funny AND I did not have one. Besides, the original throttle bracket goes for $75 at Ames! I could NOT BELIEVE that they did not have a universal throttle bracket solution to their own manifold/carb combination!!! The answer is to order a Lokar (brand) steel braided 24" throttle cable and throttle cable bracket (sold seperately). It goes in nice and easy and looks ever so sweet! The Lokar throttle bracket comes with dual throttle return springs. All of it is stainless steel. I found it locally but I believe that Summit Racing sells the same thing. |
| Q: | '67 Chrome Air Cleaner |
| At some time during my car's 32 year journey to my garage (1967 400 convertible), a previous owner put an aftermarket chrome air cleaner assembly on it. It fits badly, and tends to interfere with the throttle linkage when the throttle is mostly open (a position it sees all too often :-) The only filter that I see listed in the various catalogs that purport to be from 1967 has the louvered pancake style cover. Was this original to the 1967 - 400 car? | |
| A: | The chrome louvered pancake air cleaner came on the 1967 Firebirds with a non-AIR equiped 400 CID engine. Firebirds destined for sale in CA came equiped with AIR systems, (emissions control), which necessitated a different air cleaner on the CA 400 cars. That air cleaner was a tradition closed snorkel unit, with the top cover being chrome plated to match the chrome valve covers and breather. |
| A: | I have a '67 400 with the pancake louvered aircleaner. It was stock on the 400s that year. |
| A: | I have all the original factory chrome on my 400 and the air cleaner is the one you describe. A louvered pancake style. It was also used on vettes. There should also be chrome valve covers, breather and mc cover. |
| Q: | '68 Dual Port Advance |
| My '68 is missing the dual port advance. Is this part necessary? | |
| A: | The purpose for the dual port advance was for early emissons and with the redesign of the 68 heads that are supposed to sacvange the fuel and air to burn cleaner. |
| A: | Dual port advance mechanism was actually a retard and advance unit in one can. Tech bulletin I have states that some owners complained of popping in the exhaust due to the retard. Most dealers disconnected the retard and sent the customer on their merry way |
| Q: | '68 Vac Hose Diagram |
| I am in need of the vac hose diagram for my 68 350 ho with the dual vac advance. No a/c or air pump. The advance has been replaced with a single port which is WRONG so I want to put it back right along with the plumbing. Thanks in advance. | |
| A: |
I don't have a complete answer but maybe this will help.
There should be a themostatic control switch which mounts on the passenger side of the intake. It will have 5 ports on it. One (DA) goes to distributor advance. One (DR) goes to distributor retard. One (CA) goes to carb advance - I don't know which this is but I think (??) it is ported vacuum. One (CR) goes to carb retard - I don't know where this is. The last one goes to to manifold vacuum (at the bottom rear of the carb). If you have an Automatic, the vacuum modulator also goes to manifold vacuum. Also, the AMES catalog sells both the control switch ($35) AND correct color vacuum hose kits ($54 - ouch). They also have a pretty good diagram of a 68 4bbl in their catalog and I'm guessing they send directions with the kit. |
| Q: | '68 Vacuum Hose Diagrams |
|
Hello all! I am in the midst of rebuilding my '68 firebird 400 conv. (little by little). I am working on the engine for now, while I am waiting for my Year One parts to arrive... I read the message a little earlier about overheating. Which unfortunately, my poor car is doing! It mentioned the vacuum advance hose being on 'manifold' rather than 'ported' vacuum. I was wondering if anyone might be able to point me in the right direction for a Diagram of CORRECT vacuum hose routing (or some dang good pictures), for a 1968 400. It seems the owner before me, decided to just cap off almost every vacuum port available... so this could be one cause of the overheating... ? | |
| A: |
Links to pictures of the diagrams:
http://FirstGenFirebird.org/firebird/FAQ/docs/vacuum1.jpg http://FirstGenFirebird.org/firebird/FAQ/docs/vacuum2.jpg http://FirstGenFirebird.org/firebird/FAQ/docs/6869VacuumDiagram.jpg |
| Q: | Thermostatic Vacuum Switch (TVS) |
| My '68 400 Firebird has what I believe to be a vacuum switch on the intake manifold and there is at present nothing connected to it. Should there be? One would think there should. I have no idea what to hook up to it as all of my vacuum lines seem to be accounted for. Any helpful suggestions would be greatly appreciated. | |
| A: |
Yes, it should be there. Should it be hooked up? If you want it totally stock yes. Is it necessary? Probably not, especially if someone has replaced the vacuum advance unit (regulating vacuum to the distributor) on your distributor and you don't have a dual port unit anymore.
If you did want to hook it up, there should be five ports and they go something like this, I think: Inputs: Carb Advance, Carb Retard, Manifold Vacuum Outputs: Distributor Advance, Distributor Retard If you want to hook it up and be sure, get the vacuum line kit from AMES and ask them for directions (if they don't come with it). |
| A: | It is what's known as a thermovacuum switch.When the engine coolant temp is below the temperature rating of the switch certain ports are open to each other allowing vacuum to flow between them.Once the temp rating is exceeded the thermal pellet raises a rod inside & switches the vacuum to different port(s).This switch works very much like a thermostat.They are used for many different purposes on cars,in some cases they delay operation of some device (an EGR valve for example) until operating temperature is reached (to avoid stumbling & "sag"),other times they are used to operate a device only until operating temperature is reached (example- a vacuum operated heat-riser valve). |
| A: |
Here is the text of an article that AME's FAX'd me. Looks like it was from Pontiac Enthusiast magazine (Vol. 1 No. 2) and was written by Peter Serio:
Back when emissions systems first appeared on cars, it was almost an instant reaction to open the hood and say, "Who needs this stuff to slow my car down? Let's rip it out, plug the holes, and go faster!" Years later, it may become mandatory for vehicles manufactured in the early days of emissions systems to have fully functional systems in place. In addition, in concours competition, a deciding factor can be a detailed engine compartment with a correct and operational set of emissions parts. In addition, your car's drivability could depend on an understanding of how the emissions gear works. In the previous issue of Pontiac Enthusiast, we looked at the 1968-69 manual transmission vacuum advance valve. In the next issue, I will cover the transmission-controlled spark systems used from 1970-72. For now, it's time to turn to the TVS, or thermostatic vacuum switch. The TVS-GM#3016754 is used on all 1968 V8's and on 1969 V8's with automatic transmissions. Also, several early production 1969 Ram Air III cars with manual transmissions were built using the TVS and the vacuum advance valve. The 1971 455 HO engine also used the TVS with either transmission. In all applications, the TVS serves as a safety device to help prevent overheating. The switch is located at the front of the intake manifold, threaded into the coolant passage. There positions inside the TVS related to coolant temperature. Standard vacuum flow is ported vacuum from the carburetor to the distributor vacuum advance. Whenever the engine coolant temperature rises above 230 degrees F, the TVS switches the distributor advance from ported to full manifold vacuum. This advances the timing about 20 degrees at idle, allowing the engine to cool down to normal operating temperature. After the engine cools, the system returns to ported vacuum. If your car does not have the system hooked up properly, it could overheat on a hot day when you're stuck in traffic, which could reduce the life of your engine. In 1968 the fan shroud become standard for the GTO, whereas in earlier years it was an option on non-air cars. With the idle retarded in 1968 to reduce idle speed emissions, the switch's purpose was to advance the timing when necessary to allow the motor to cool down, to prevent pinging. A manifold connector in the vacuum hose harness to the TVS is used to prevent the hoses from being installed improperly. Note that some of the vacuum hoses in the harness have color-coded stripes running on the supply lines to the TVS. The red-striped hose is manifold vacuum, and the ported vacuum is routed through a small steel pipe forward of the carburetor. The yellow hose (used in 1968 only) is the retard-at-idle-speed vacuum supply. There were two different hose harness assemblies used, depending on the year of the car. In 1968 only, with the dual-port vacuum-advance unit attached to the distributor, the idle speed timing is retarded 10 degrees to reduce emissions. After the '68 models, all distributor-advance units were the standard single-hose-connection style. All the '68s use the 5-hose vacuum harness, while the '69 V8's and '71 455 HO make use of the 3-hose type. The two extra hoses on the '68-only harness are the idle-speed retard feature. Apparently it did not take long for dealers to receive complaints that some of the '68 cars idled poorly, and Service Bulletins 68-T-2 (dated 10/16/67) and 68-T-2A (dated 1/4/68) were released. Models affected were the '68 Firebird, full-size, and Tempest/LeMans/GTO with the 2-barrel carb and automatic trans, plus full-size automatics with the 4-barrel. The complaint was that the second-to-first downshift could clunk badly due to the retarded timing. Manual-transmission cars were unaffected, since the idle speed was higher and you shift your own gears. The procedure outlined in the bulletins basically involves removing the two vacuum hoses that retard the timing at idle; shortening one and connecting it to the two switch holes in a U to keep dirt out of the holes; and readjusting the idle speed. If you have a '68 2-barrel automatic or full-size 4-barrel automatic, these Service Bulletins would be a nice item to search for. |
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From the '68 Diagnostic Manual: Fig 6D-9 Components of Controlled Combustion System http://FirstGenFirebird.org/firebird/FAQ/docs/6D-9.pdf Fig 6D-10 Distributor Vacuum Layout V-8 2 Bbl. http://FirstGenFirebird.org/firebird/FAQ/docs/6D-10.pdf Fig 6D-11 Distributor Vacuum Layout V-8 4 Bbl. http://FirstGenFirebird.org/firebird/FAQ/docs/6D-11.pdf Fig 6D-12 Vacuum Routing Chart http://FirstGenFirebird.org/firebird/FAQ/docs/6D-12.pdf Fig 6D-13 Vacuum Routing Chart http://FirstGenFirebird.org/firebird/FAQ/docs/6D-13.pdf Fig 6D-14 Vacuum Routing Chart http://FirstGenFirebird.org/firebird/FAQ/docs/6D-14.pdf |
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Jim, a list member from the First Generation Firebird-L Mailing List, did research on this compairing all the documents available and put together his findings: http://FirstGenFirebird.org/firebird/FAQ/docs/TVS/68VacuumDialog.pdf |
| Q: | Distributor Vacuum Advance Valve Assy |
| Was the Vacuum Advance Valve (control) only on Firebird's, or was this also on GTO's ? Was it installed on any `68 Pontiac with any manual trany ? | |
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The Distributor Vacuum Advance Valve Assy was used on
all '68/'69 Pontiac's with Manual Trans and the '67 M.T. A.I.R. engines.
# 9773623. It was attached to the RH Rear of the Intake Manifold.
The Plastic Cover on the end should be Black. On the RAII engines, this
cover was Green (#9794257).
This should not be confused with the Distributor Vacuum Control which attached to the Distributor itself. Both are available NOS now & then. |
| Q: | Dual Diaphragm Distributor |
| I am having a problem with a slight backfire and someone told me to disconect one of the two hoses to the distributor. Is this correct? | |
| A: |
68 was the only year for a dual diaphragm (advance /retard) distributor.
It was to retard the distributor under certain conditions for emission
lowering. A service bulletin was issued for dealers that got complaints
to disconnect the retard side. A lot complaints of a slight backfire
on coasting downhill and deceleration . Such a tech service bulletin wouldnt
be issued today as theres a stiff fine for modifying or removing any
emission device
Chances are the retard side has been disconnected on yours.
Look for a separate vacuum hose nipple on the distributor advance/retard
control "thingy".If its been removed,hope that the vacuum source has been
plugged off.
From the Pontiac Service Information Bulletin: http://FirstGenFirebird.org/dtb/docs/68-T-2.pdf http://FirstGenFirebird.org/dtb/docs/68-T-2A.pdf http://FirstGenFirebird.org/dtb/docs/68-I-45.pdf |
| Q: | '67-'68 Firebird Q-Jet 'tab' |
| Does anyone have information of the bent tab used to limit the horsepower for the carburetor found on the 400 Firebird. | |
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For many years, it has been widely accepted that the
major difference between the 400 Firebird and GTO engine
(1967-1968) has been the carburetor. Factory/Dealer specs
listed the Firebird 400 at 325hp for '67 and 330hp for '68.
The GTO was listed as 335hp for '67 and 350hp for '68.
All 400 HO & Ram Air engines for both models were listed
as 360hp for '68 ('67 Firebird RA was listed at 335hp).
No where in the factory/dealer literature is there a mention of a different throttle bracket, tab or linkage preventing the Firebird secondaries from opening as far as the GTOs. There have been several articles & publications over the years that have refered to such a variation on the Firebird Carb. Hot Rod Magazine- 3/68 "...in order to produce the advertised horsepower, there is a small tab on the throttle shaft which actuates the secondaries, but only to two-thirds open at full-throttle. Somehow you don't feel guilty at bending it rearward." Special Interest Autos- 10/86 "..The 400 was detuned to 335bhp by adding a small metal tab in the throttle linkage which slightly limited travel of the secondaries. Needless to say, very few of these tabs remain today where GM put them." Motor Trend- 12/91 "...GM only agreed to install the 400 engine if it could restrict it's performance, which meant it placed a stop on the throttle linkage that prevented wide-open throttle. Of course, that could be removed by the owner in about 30 seconds." (Jim Wangers) The Fabulous Firebird- M.Lamm- 1979 "...Yet to stay within GMs horsepower ruling (1hp for every 10lbs), Pontiac not only derated the Firebird 400 V-8 to 325 bhp but also modified it so, in showroom form, it truly wouldn't produce more than 325 bhp.... by simply changing the link between the primary and secondary barrels of the Rochester Q-Jet carb. This link was arranged with a steel tab that didn't let the secondaries open more than 90% at full throttle." Firebird Decoding Guide- T. DeMauro- 1997 "A throttle linkage restrictor installed on all Firebird 400s stopped the rear two barrels of the Quadrajet from opening allthe way, thus limiting horsepower and keeping the car within the 10-lbs to 1 hp Gm corporate edict." So, as you can see, there was obviously something different between a GTO carb and a Firebird. Surely all of these articles were not simply created from simple rumors or suspicions but from experience. Many references were based on modifications by Royal Pontiac during prep for an article (to squeeze out more performance). No mention was ever made about the difference in the exhaust system. If anything, the HO and Ram Air Firebirds had a better exhaust system due to to Long Branch Exhaust Manifolds. As for defining the actual component on the carb. and how it was different, there needs to be a photo comparision to better explain this. The above excerpts seem to refer to the same thing; a tab on or a part of the throttle linkage. I am currently going through my files and pulling up detailed photos and illustrations I have pertaining to this matter. If anyone has an original '67/'68 Firebird 400 4Bbl Carb. and wouldn't mine taking a few close-up photos (RH & LH side), I would be glad to follow-up on this and post the final comparison photos. |
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I seriously doubt that the Rochester plant earmarked certain carbs for Firebirds and bent the tabs. How would you explain the carbs that the GTO and Firebird both share same part #? Same part # means same part. Period....
The reason for different part #s of certain models of Firebird vs GTO was that the jetting was different. Base plate assemblies which have the throttle linkages attached are the same part #s between GTO and Firebird. |
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After initially researching this through careful examination
of original, unrestored cars, an extensive detailed photo collection
and checking the carbs I (and friends) have, I too was convinced
that both Firebirds and GTO carbs were assembled using the
same Rochester components. The only possible explanation
would be that the lower tab on the inner Throttle Link could have
been bent to prevent full travel however, I did not find this in
my research (all have been corrected ?).
Then, I received a reply from Paul Spotts who claims to have an unrestored Firebird carb with this modifed (bent) tab in place. He also says this link was a different part number and that he submitted an article to HPP that explains in detail (w/photos) this entire issue. So, I guess we'll wait and see if it gets published. In the meantime, I'm continuing the search. As for the shared part numbers for GTO & Firebird, I've noticed that over the years (following production), different Parts Catalogs start combining the usage for carbs (typical service replacement procedure). Also on a related note, I recently came across an early 'take-off' 7028277 RA I carb and spent a great deal of time comparing it to a 7028267 carb I have. Other than the Rochester I.D. stamp (for specific usage), there was absolutely no other difference with regard to Rochester component numbers. Every stamped or cast number was identical on every piece. Interesting. |
| Q: | "Numbers Matching" |
| How do you know if you have a numbers matching car. | |
| A: | People still call cars "numbers matching" if all of the Part Numbers and Casting Codes are correct and pre-date the car by the correct 1-3 months (in general). |
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Use the following web pages on the First Generation Firebird web site as a guide: 1967: http://FirstGenFirebird.org/firebird/1967/id_numbers.html 1968: http://FirstGenFirebird.org/firebird/1968/id_numbers.html 1969: http://FirstGenFirebird.org/firebird/1969/id_numbers.html |
| Q: | Date Code |
| On 68 quadrajets, where is your date code stamped? Not on the body next to the Rochester number, but on the base, right? Anyone with a 69 have it on the base also? | |
| A: | ...I've seen and have (or had) '68 Rochester Carbs with the Julian Date Code stamped near the Model Number on the Body and on the Base at the back. I've also seen them with no date code at all (RA I 7028277). I suspect that early '68 Carb's were most likely to not have the date code or for it to be on the Base. |
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