Can anyone help me out with a couple of questions. The car has never pulled as hard as I have thought it should. I am pretty sure it is a carb related issue as it also bogs initially upon hard acceleration. I have not been able to confirm a couple of items. The first is the vacuum lines. I believe I have them correct, but can anyone confirm via the pic? The online online information is somewhat conflicting:



The second one is what are the two screws on the base of the carb for (fuel/air?)? It sounds silly, but I have not seen them on the diagrams I have found. How are they properly adjusted?



Also, is the paint burning off of the center fuel passeges on the intake any indication of a problem?

It depends on if you are using the early '68 or the post-service-bulletin configuration. And that depends upon whether your distributor vacuum advance has one or two ports, and if your car was subject to the bulletin. If it has one port on the front of the vacuum canister and one on the back, you can use 5 lines. If not, you must use the three line configuration.

https://firstgenfirebird.org/dtb/docs/68-T-2.pdf
https://firstgenfirebird.org/dtb/docs/68-T-2A.pdf

If you take off the adapter plug, the ports on the TVS are marked. CA=carb advance (vacuum port); DA=distributor advance (front of vacuum canister on distributor), DR=distributor retard (back of distributor vacuum canister), CR=distributor retard. There is also a vent port.


Those are the idle mixture screws. They control how much fuel goes to your engine at idle.

Reference: http://thefirstgensite.com/library/qjrepair/qjservice1981.pdf
http://thefirstgensite.com/library/68sm/engfuel/engfuel.html

Also check the position of your accelerator pump lever, and the tension in the secondary air flap spring.




Nope, that's normal.

I'll give the 3 hose vacuum diagram on the FAQ page a shot and see what happens.

I hate carburetors... That manual is 46 pages of pure evil to me.

It does not give concise adjustment procedures. It is full of if this and on 'modified' that, and some use this while others use that and don't forget that if this is adjusted that way, make sure this is turned the opposite way, but NEVER on a Tuesday.

AAAGGGRHHHH!

Can't they just say turn the screw X until it is tight and then back it off X turns?

You can, for starters. With the engine off, turn each of the idle mixture screws clockwise until lightly seated. Record the number of turns for each; they should be very nearly even.

Back each screw out 2 1/2 turns and run the engine until warm and the choke fully off. Turn each screw clockwise 1/2 turn and see if RPM drops or engine stalls. If so, back out each screw 1/4 turn and repeat. If not, turn in another 1/2 turn each. Ideal will be just at RPM drop or a little leaner (clockwise is leaner). Be sure to turn both screws the same amount, alternating between them.

I've had Quadrajets with the "ideal" at 2 1/4 turns out, others at 3 1/2.

That is the kind of info I am looking for. I did this and it is already running better. I am at about 2 turns on both before RPM's start to drop. I will pull out the timing light and start over from scratch now that I am closer.

Tim

Hook up a vacuum gauge to your intake manifold. Then adjust the idle adjustment screws to maximize vacuum at idle.

The bog you're getting is likely a poorly adjusted secondary air valve spring. Too little spring tension and the secondary air valve opens too soon letting too much air into the engine. Too much spring tension and the secondaries will open too late, spoiling your fun.

Just an FYI, the center cross-over on the intake is the exhaust cross-over that's why it is discoloring faster than the other runners. It gets hotter.

Thanks for the head up.

John, I will be borrowing a vacuum gauge later this week and will try out what you suggest. (As soon as we get un-buried from this stupid snow storm again!)

catalina, I hope you don't mind if I also ask a Q-jet question in this thread.

I also have a bogging down issue at the top of second & third gear. Just as I approach 5k RPMs or just a bit over the car falls flat on it's face. I have to back off the throttle and let the car "recover" then I can get right back into her and she takes off again until the top of the next gear.

Does this sound as though I am running out of fuel at the top end of each gear? Once I get this issue resolved I can finally run the dyno again...

That's happening long after WOT so I doubt it's a bog like I mentioned earlier. Fuel starvation makes sense. Where's TOHCCAN?

All I know is that this issue is really aggravating because the car pulls so hard and quick, then all of a sudden this happens at the top of end of second & third but does not do it in first...

I imagine you're not in first gear for very long.

True however, RPMs would be the same basically. Just getting there a lot quicker...

Ignition issues can also cause high rpm fall-flat.

One way to check for a fuel delivery problem (which it certainly sounds like to me) is to get up to about 4000 rpm in second gear, hold your speed for about five seconds then punch it. If you don't get the bog this time, it's time to check your fuel pump, filters and fuel lines.

Fuel delivery issues show up when the engine pulls for a long time at higher rpm, just like you get in the higher gears. You can do some nasty things to the engine if you don't fix a lean condition. Having the engine recover a few seconds after cutting out is a pretty definite sign of fuel starvation.

Just a quick note, a friend of mine rebuilt his carb and had some serious starvation problems after - he put the little carb filter in backwards! It barely had enough fuel to get to 50 mph!

I take it, it was the paper filter not the sintered bronze filter.

I have replaced my paper filer as well as all the rubber sections of gas line from front to back. I am going for a run now and will try the suggestion...

FWIW, if it were an igniton problem, it wouldnt just do it in 2nd and 3rd.

Ok went for a ride and tried the 4k then nailed it. Same as before takes off great until just after 5k begins to break up, sometime much worse than others but will almost always do it up in the high RPMs.

I'm thinking of making a video if it from inside the car I wonder if you guys would be able to hear it/see it etc. Might try that later on...

How does it sound when it "breaks up"? You described it as a bog before, now as breaking up - does it cut out competely or start missing?

Definately not a "break up" more of a bog/stall type thing. Let off the gas and bang she comes right back. The car hits 4900/5000 RPMs and bang, falls flat on it's face. If I shift just prior to that, no issues. It just sucks because you can't top out 2nd & 3rd due to this issue.

I had this problem at the track last Nov. at the stock appearing drags. I was running against by buddy's 68 GTO, he cut a .005 and I had a .450 off the line and in first gear at the 60' time I was almost caught up to him and pulling stronger, then comes second gear everything is good, then hit the top of second, blah choke and away he went. I was so mad! LOL

Also, I do NOT get ANY backfire at all when this happens. Not sure if that helps or not but it has never backfired on me when this happens...

sure sounds like you're running out of fuel...

Thats what it seems like, feels like too me...

Does sound like fuel issue.
My 1st guess would be fuel pump go'n.
2nd would be fuel filter.
I use an inline can filter. None in the carb.
May want to check carb float level too.

New filter and pump.

Not sure how to check float?

I think Vicki is onto something, you should double check your secondary ignition(cap/rotor wires and point set-up if your running them) and go from there. If possible have the ignition scoped, that will definitely find the problem if it is ignition related.

Got to check all the factors.

Let us know.

im having the same trouble with my ohc sprint
first time was the power valve or plunger .then a slit in vacume line
rebuilt a new carb 4 it still have to put it on lol
its like u have to feather the gas some times right.
could be a pice of dirt but doubt it . resticted fuel filter
bad fuel pump check oil make sure your not getting gas mixed in the oil to could be costly.
these r just guesses of corse just some of the trouble ive had lol good luck and message wt it was

Ok, to eliminate some of the suggestions:

Vacuum lines are good.
Rubber sections of fuel lines have all been replaced.
Fuel filter/pump have been changed.
Dist. was changed from Pertronix II back to points problem existed with both.
All new plugs, wires, cap, rotor & points.
Timing is dead nuts as per dist. set up specs.

Charging the camcorder now. Going to take a ride in a bit and will make a video clip and post it. See if you guys and gals can hear/see/feel what it is exactly the car is doing.

I am fairly certain that it is in the carb. I feel it needs to be rebuilt. This is a carb. that I purchased from Terry almost 3 years ago. Brought it home and installed it on the car. Poured fuel into the bowl and she fired right up. Havn't done a thing to it since that day.

After checking the numbers it did come up as a 74-76 Pontiac carb. Could that in itself be an issue? Wouldn't it be set up for a leaner engine based on fuel conservation from that time period?

My friend did pull the metering rods out to see what number they were, to his surprise there were NO numbers on them. I think it may be time to get a rebuild kit and then install the correct metering rods and jets for my engine & year.

First, let me again appoligize for totally hijacking this thread. I'm hoping catalina's question/issue has been resloved.

Well, much like taking a car to a mechanic, my wife and I just took the car for a drive. Low and behold she did not fall on her face at the high RPMs. The only difference being possibly is that it is unseasonably cool tonight at barely 60* and a very cool breeze to boot. Now I have noticed in the past as well that in cold mornings or evening, especially if the car has been sitting, she usually will not break up etc.

It's not a problem at all. I would like to see this thread keep going...

I just got a vacuum gauge today and will work on it as soon as I can.

Looking forward to the vid...I had the same problem a few times, one of them racing my partners Audi convert down a straight stretch... bogged out and he took me. I asked for another try and it was fine and I blew his doors off. It still does it once in a while, about once a year...so I have not delved in to it to hard, but I am watching this thread. My carb is a professionally restored oroginal Q-jet as well.

Going to upload a couple of vid clips to my photobucket site. Although the car did not bog down, maybe one of you might pick up on something. It will take a while to upload...

Who rebuilt your carb . how long did it take and how much lol
im tired of guessing and wrenching lol pm me plz adress

I am uploading one now where I start out in 1st gear, did a slight burn out, and you will see how the car falls flat and then recovers. This was the first time it ever did it in first gear and was the only time it did it tonight...

If you crank up the volume on your PC you will hear the engine bog/chug right after the burnout, then she takes off again. I had forgot that the car did this until I replayed the video clip...

just a wild guess here... but could it be a mild case of vapor lock?
I remember going to the Fremont drags on grudge night, and we'd have to wait idling in a long line of cars. By the time I'd get to the start line, it would often run rough due to vapor lock. Is the underhood area exceptionally warm? Is the fuel line running against any hot areas?

I'd say fuel starvation for sure. First thing I'd suspect is the accelerator pump, then float level. The carbs rebuilt within the last five years are going to have components that are compatible with today's fuels. Outside of that, components will deteriorate. It boils down to what the carb was rebuilt with, since there's NOS kits out there. The smog carbs did run leaner, but that shouldn't have the effect that you're experiencing.

Case in point, I bought a NOS reman 1bbl carb a year after I bought my cammer. After installing it, the car ran great! But six months later, I started to get a whiff of raw gas. I didn't see anything until it started staining the intake. So I had to buy another reman carb that was put together with current fuel acceptable parts.

You don't need the sound turned up. You can see your nose drop when you hit the flat spot.

I still think you'e running out of fuel but, I don't know why. Based on what you've alreadt stated, I'd check the float level. Unfortunately, you have to pull the top off the carb to do that... Hopefully, one of our resident carb guys will chime in.