Flat spot or bog???

[staged67gspwr]

The q-jet on my `67 GS Convertible has a flat spot or bog i shold say when i`m increasing into the throttle,i know its not the original Q-jet,i think its off a cadillac or something,what can i do to stop this?i adjusted it as best as i can with vacuum gauge but still doing it,can i purchase a rebuilt kit from somewhere?any suggestions?dont know too much about these carbs as i`ve always dealt with Holleys.

Thank you

[68 LeSabre 4dr]

Grab the #'s off the right side George and call Napa for a kit . Good Luck George :Brow: :TU:

[staged67gspwr]

the #`s are 7027231

[71GS455]

It could be the air valve tension spring for the secondaries. This is on the passenger side of the carb. There's a set screw and a slotted screw.

Hold it in place with the slotted screw as you back off the set screw. Tighten it about 1/8 of a turn. See if this helps remove the bog. If not, try another 1/8th.

It could be that the secondary air valve is tipping open too early. I had this problem with my 71 GS455 after I changed to a Performer.

[staged67gspwr]

where exactly is this screw?between the primary and secondary?

Thanks

[71GS455]

It's on the passenger side of the top of the carb back by the secondaries (where the air valve plate hinges).

Here's a pic with the set screw and slotted screw circled off a 76 Buick QJet (only one I have at hand).

The set screw aims down from above and the slotted aims towards the passenger side of the car.

[staged67gspwr]

Steve so just basically turn it clockwise or counter clockwise?

Thanks

[71GS455]

Sorry George,
I posted this just before watching a dvd.

You'll want to put your screwdriver in the slot and hold it while you loosen the set screw, since it's under spring pressure.

Tighten it clockwise to add more tension to the air valve. This should delay it from opening and is what helped me get rid of my bog. Loosening it makes the air valve open quicker, which seems like it would be good, but it doesn't allow a smooth transition into the secondaries - thus the bog.

[staged67gspwr]

will try it today and give it a shot,i`ll let you know what happens.

Thanks

[71GS455]

Good luck, George!

[staged67gspwr]

thanks Steve.:TU:

[staged67gspwr]

Steve,still the same problem,i had to take the carb off because i turned it too much and the spring came off,i have it as tight as i can before the spring falling off but still getting the bog or flat spot,what else can be causing this?

Thanks

[Keith2k455]

George,
Typically when a carb. bogs it's because you aren't getting enough fuel in the mixture at that point in time (why turning the air valve may help). I've never tried to tune a quadrajet, only my demon, but I'd go along the lines of your mixture, your accelerator pump may need some adjusting, or something else along the lines of air/fuel. I tend to believe if you were to buy a rebuild kit you would probably have a rebuilt carb with the same problems, but that's just the way I'd look at the situation.

[MT BUICKNUT]

George make sure that your vacuum choke pull off is good and not shot. If that is bad it will allow the back secondary doors to flop open. Good luck
Rick

[Leviathan]

I'll second Rick's analysis, this sounds like the infamous secondary pulloff failure.

The seondary pulloff should be all the way in at full vaccum, and then pop out in just over 1 second. If it does not do either get it replaced. Test it with piece of vaccum hose that you can suck on. NAPA is just about the only parts place left that carries secondary pulloffs.

Note that it is the pulloff, not the spring that regulates the air door opening. the spring is only a damper and should only be tight enough to let the doors close.

If the air dam cannot be adjusted to correct the problem then go for a total rebuild. It's about $60 and will really improve the idle and WOT power. Ifyou're unsure about doing it yourself, talk to John Osborne about getting a rebuilt one for your Buick, he's the best in the business.

270-737-4467 JOP455@AOL.COM


Some more info for you based on the 7027231 number:

70: the carb is a pre-smog era unit.

27: 1967 Carb.

2: 49-state emissions.

3: Cadillac.

1: Manual transmission setup.

[71GS455]

1967 Cadillac with a manual trans!? :TU:

[staged67gspwr]

Where or what is the secondary choke pull off?sorry guys i really dont know sh@t about these carbs.

Thanks

[MT BUICKNUT]

George they are the little round things on the pass side that have vacuum lines to them. The Buicks have 2 I don't know about the Cad ones. If its bad your motor will bog like crazy out of the hole and take off like a raped ape.
Rick

[71GS455]

From the 76 Buick 455 Qjet:

[staged67gspwr]

ok cool,i`ll check that out tomorrow,i`ll let you guys know how it works out.

Thanks

[Leviathan]

staged67gspwr said:sorry guys i really dont know sh@t about these carbs.

Hey, that's what the board is for! If you want to get into `em though, pick up Does Roe's Quadrajet book and do a rebuild. You'll be a carb guru overnight! :TU:

[staged67gspwr]

ok switched the secondary pulloff because it was not working,now that works but still have the bog or flat spot?:mad:

[RAbarrett]

Before making recommendations for this problem, I need to know exactly where the bog occurs. Is it during light throttle tip-ins, or on heavy accelerations? Is it from a stop, or when changing speeds? There are several systems involved in driveability, and knowing exactly where the problem occurs, and under what conditions will help. I see from your responses that you are a novice; we were all there at one time. I will need to know whether the problem occurs cold, during warm-up, and from what speeds. ANY info provided will help. I have some 35 years experience with driveability, and will help where I can.

[staged67gspwr]

Hi,the bog or flat spot occurs when i`m under light throttle tip ins and under heavy acceleration as well,it wont do it from a dead stop but as i`m increasing the gas pedal,it will do it whether its cold or hot,any help appreciated.

Thanks

[RAbarrett]

These carbs were known for sticking power pistons, especially when used very little. I suggest using a pocket screw driver to test the power piston thus. Looking down the bowl vent, there is a lever, which is controlled by vacuum against the pressure of a spring. Try gently pressing down on the lever, to see if it is free. If not, that is the place to start. Talk to me.

[staged67gspwr]

I dont think its free as it doesnt push down at all either with motor running or not running,what do i do from here?

Thanks

[RAbarrett]

It may be necessary to open the carb, but try this first. Using carb cleaner, attempt to free the piston by spraying it into the cylinder, and tapping it gently with a screwdriver. You will need to be sure you are on the piston, however, if nothing responds to the prying screwdriver, it is definitely stuck. Before attempting any other troubleshooting, this piston will need to be freed. I would try purchasing an air horn gasket and carefully removing the air horn, if necessary. If you are a novice, it could easily cramp the old spinctometer. It will require the disassembly of the choke linkage, accelerator pump, etc, but careful disassembly will be possible. I would also, at this point recommend Roe's book on this carb. It is cheap insurance.

[Murphy]

I have the same problem with my carb. It's on a 68 400. Here are the #'s off the carb 7028246 . I have read this thread about 3 times now. I did adjust the screw to adjust the spring tension for the secondaries. How tight should this be? I tightened it 1 whole turn, a little at a time. It did help, but should I go more? I also know very little about these carbs and any help would be great. I hope this is ok here, I didn't mean to hi-jack the thread
Thanks,
Dan :3gears:

[staged67gspwr]

Power piston spring was missing,good thing i had another spare carb laying around and took it out of that one,i`ll let u know how she runs.


Thanks

[RAbarrett]

I am pleased that these forums are helpful. To those tuning their carbs using springs or spring adjustments, please be advised that these primary springs calibrate the movement of the metering rods, which will determine the consistency of the mixtures throughout the primary performance areas. If the wrong ones, they can cause rich or lean running, but would still be better than none at all. They can be used to tune for different engines. On the secondary side, the spring adjustment is not the only air valve tuning aid. The choke pull off (on most carbs) is also connected to the air valve linkage, allowing the valves to open only as fast as the pull off extends with the loss of vacuum. Different pull offs will affect the secondary air valve performance as well.

[staged67gspwr]

Running alooooooot better almost perfect but still has a very light hesitation.

Thanks

[Buick_350X]

Heard of a trick once of sticking a paper clip under the secondary metering rods thingy. This raises it slightly and is suppose to kill hesitation as it just help to get them opened up a hair sooner.

Never tried it though.

[Smartin]

hmm...

What secondary rods are you running? And what hanger?

[staged67gspwr]

dont know,never touched this carb,its a stock carb.

Thanks

[RAbarrett]

As previously mentioned in the replies, the time of the hesitation is important to note. If during warm-up, it could be a choke opening too quickly. If just after start-up, the choke pull-off could be set slightly too wide. I suspect one of two possibilities; either the accelerator pump is weak, of the spring you are using is incorrect for the application. This will show up even with a warm engine. There are several possibilities regarding emission controls as well, including the air cleaner not warming the incoming air, or the heat riser is not heating the intake manifold. Let me know...

[staged67gspwr]

Hi Ray and guys,i finally took off the `67 Cadi Q-Jet and replaced it with a `67 Buick Q-Jet,i got it rebuilt with new old stock parts from Buick Farm,after installation for a few days it ran excellent then i noticed from a dead stop it would have a very light bog when giving gas to go and still does,i checked a few things myself but turn out good,at this time i really dont know what else to look at anymore :Do No: .then the other issue i have is i cannot get the fast idle to work properly,eveytime i screw the fast idle screw to get the high idle to about 1100 rpms and then tap the gas to drop the high idle i cant lower the regular idle after because there isnt anymore adjustment on it to lower it?

Thanks

[RAbarrett]

From what I see, it appears that both problems are related. The Q-jet has a transfer slot to enhance fuel delivery during transient maneuvers. It basically enhances the accelerator pump, and creates another fuel delivery mode, further refining the carb to meet emissions. If the idle is not properly adjusted, the result will be a sag, or hesitation, since either the transfer slot will not feed, or will not fill. Let's try this. On the Q-jet, there are two idle screws, one for the slow idle, the other is for the fast idle, when cold. The screw for the slow idle is on the driver's side of the carb, the one you can easily see. Adjust this screw for the slow idle. On the pass side of the carb, almost completely hidden behind the linkages, is the fast or cold adle adjusting screw. It is visible from the front of the engine, typically black in color, and requiring a Phillips screwdriver to adjust. Find a long one for this, as the adjustment will be difficult otherwise. Us the factory specs to begin with, but expect to slow it slightly to customize it for the vehicle, and your driving habits. These adjustments are made allowing the choke's adjustments to vary. Since we adjust everything to the gnat's ass, these adjustments will likely cause a very fast idle. It is critical that you understand the operation of the choke, and make adjustments that will address the problem, not just speed the idle up to compensate for the defect. Since I am familiar with this operation, I would be happy to answer questions. To me, the only dumb question is the one you do not ask. Ray

[NOTNSS]

Would a gear change cause the carb to bog? I swapped transmissions from TH400 to 200-4R which equates to a lower 1st and 2nd gear and both my Osborne Q-jets bogged off the line at Las Vegas. We adjusted the secondary opening rate and were making progress but ran out of time to get it just right. Only change in the car from last year at LV was the transmission. The air wasn't as good there this year but even the higher altitude carb I tried bogged and then would pull pretty good once I got past that.

Then I find out the tranny slips 1-2 so have issues there. I managed to lose 0.3 in the 1/4 instead of gaining that like I'd hoped (12.91/105 vs. 12.61/107 last year).

Thanks.

[RAbarrett]

When going lhigher in ratios (lower gears), you typically need to go leaner, which should not cause a problem unless they carb was VERY rich to begin with. When going lower in ratios, higher gears, it is possible for the metering to require more fuel, especially with emissions metering. It is a matter of engine loading. The more load the engine sees, (lower ratios), the more fuel it will need. This usually benefits the builder when he swaps for lower ratios for the street or track. Note: 3.73:1 gearing is higher in ratio than a 2.56:1 gearing.

[staged67gspwr]

All seemed ok for a while till recently the freakin carb started to pop through the secondaries when gas is floored?what could cause this?another thing i noticed is it has a slight hesitation when i`m stopped and i give gas to go??these freakin Q-Jets are drivin me nuts :Do No:

[RAbarrett]

It sounds to me like the secondary metering rods are not responding to the air valve opening. You can check this by observing them with the air cleaner removed. With the engine off, slowly open the air valves. The metering rod hanger between the air valves should rise as the air valves open. These carbs are known for eating the cam operating the hanger, which will allow extra air, but no fuel. Qjets are complex, but knowing what to observe simplifies these to child's play. Ray

[staged67gspwr]

I wil check it out tomorrow,do you mean the secondary flaps when saying air valves?this thing is driving me nuts,i feel like chuckin it in the river :af:


Thanks

[staged67gspwr]

How would i know if they are good or not?if they`re bad where do i get them from?i have a couple of spare carbs are they the same?

Thanks

[RAbarrett]

The secondary cams for all of the Qjets are the same. The differences come from the metering rods and hangers. My concern involves the point of hesitation. If this occurs off idle or on light tip-in, the secondaries are not the issue. The ratios for the 2004R are somewhat higher numerically, meaning that the carb should have been a little rich. If you advise me of EXACTLy what is happening, I can help you. Let me know... Ray

[staged67gspwr]

Ray,give me your number and i`ll call you right up.

Thanks