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:
ok switched the secondary pulloff because it was not working,now that works but still have the bog or flat spot?
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.
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
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.
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
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.
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:
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
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.
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.
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...
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 o 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
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
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.
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.
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 o No:
