MY CARBURETOR WILL BOG AND BACKFIRE ON TAKE OFF,BUT IF I ROLL THE CAR AND PUNCH IT TO THE FLOOR ITS FINE. CAN ANY ONE HELP ME WITH THIS PROBLEM?o No:
The first thing I would do is check all the basics first- dwell, timing, and carburetor adjustment. Check all the components of the ignition system as well. Cap, rotor, wires, spark plugs, etc. make sure you adjust the carb with a vacuum gauge and note the readings. Once you have the ingition system up to snuff, and the car is tuned properly, you can re-test for your driveability issue Its a possibility that the accelerator pump is bad as well. Most vacuum gauges double as fuel pressure gauges. I would do a quick fuel pressure test to rule out a pump problem. Test, dont guess
Jason, Good call with the test, don't guess. Also a good call with the basics, especially with the ignition. Points ignitions were relatively weak, and sneezing without covering your face could lead to issues. One other thing to check is that, with cooler weather, it is possible that the thermal air cleaner snorkel valve may be completely open, even cold. Though this improves power, these carbs are calibrated lean, and the cooler air could lead to issues as well. After addressing the ignition issues, we'll discuss possible choke issues, especially with cooler temps approaching. Ray
Hey Snake I Have Hei High Performance Distributor And A New Q-jet 4 Barrel. What Can I Set My Timing To ?
Thats all depends. If the engine is bone stock, I would set it to the factory specification first. We need a good baseline before we can go any further Does your timing light have an advance knob?
Here we go again:laugh: Another candidate for my Power Timing thread. http://www.v8buick.com/showthread.php?t=63475 Set the total timing to 32* to start, then go from there.
It can also be the secondary tension spring is set to loose and openning the secondaries way to soon. This causes a temporary lean condition. It should more be like a cough or a berp . There is an allen screw with the head facing down towards the engine near the rod that conects to the secondary top butter fly(passenger side of the car. This is a set screw for the small screw that is under that rod bracket. This screw adjusts the spring tension for the secondaries(takes a small flat tip screw driver). Loosen the allen screw and rotate the the spring tension screw to the right a smidge at a time(a 1/16 of an inch rotation at a time). Take it out for a test run(warmed up of course) and keep adjusting untill the cough goes away. NOte: when you loosen the allen screw you have to have the screw driver on the adjustment screw or else the spring can unwind. I have been messing with these Qjets for years, they are a great performance and reliable carb when you understand how to adjust them. They keep there set unlike Holleys and E'brocks
"Hey Snake I Have Hei High Performance Distributor And A New Q-jet 4 Barrel." They haven't made "new" Buick q-jets for decades, where did the carburetor come from? Secondary stumble/hesitation/bog usually comes from a lean condition as the huge secondaries first open. Basically, not enough fuel delivered in the correct amounts to the incoming air. So we have a conditions where the fuel is simply not being supplies fast enough or in enough quantity, or the secondary airflaps are opening too quickly. There are several places to check in your quest to correct this problem. The spring tension of the secondary airflap shaft (grease the pin the spring slides on). The secondary cam. Hanger height. Metering rods. Primary accellerator pump. Secondary pull-over enrichment (POE). Primary choke pull-off. Link from the pull-off to the secondary airflap linkage. Fuel sloshing out of the vent(s) into the secondaries (typically not a problem on slower cars) These days with ethanol in the fuel, one of the first places to check is the accellerator pump. Weak or insufficient pump shot causes an instant delay when the secondaries are applied quickly. Weak duration and delivery springs, or even the wrong pump being used (common problem, folks buy aftermarket "high performane" pumps that are too short, or they cut too much off the shaft of the stock pump, causing a slight delay in fuel delivery). While I'm mentioning aftermarket pumps, for some reason I will never figure out, they use a duration spring that coil binds (very bad), and supply a spring under the pump with as much or more tension as the one on the pump (it ain't gonna work). Check the pull-off, for a bad diaphram and too fast of an opening rate. Make sure it is holding the flaps tightly shut at idle or high vacuum situations. Secondary airflap spring tension. Cam worn, cracked or loose on the shaft. *This is a problem that is missed by even experienced tuners. The cam and spring should be replaced on every single q-jet being built for any level of performance. POE tube or tubes have fallen out of the airhorn, not all that common, but it happens. Bent hanger (common problem as well), or the wrong metering rods being used. Hangers get bent when folks install the airhorn with the secondary metering rods in place. What often happens during tuning, is that the tired/worn out secondary spring gets over-tightened, which masks the real cause of the problem, and hurts overall engine performance. Basically, it's a lot of items working together, but it a very good system, and when set up correctly will allow seamless transition on the secondaries and excellent power transfer to the tires. You should never "feel" any "hit", "kick" or big "lunge" when the secondaries come in. Even when it doesn't stumble, tune the system until it is "seamless". About all that should happens is that you are looking for the shifter and trying to keep the vehicle pointed straight when you launch it at full throttle! .....Cliff
Something not mentioned here is the temperature at which this problem occurs. If it occuring during warm up, it is very possible that the choke is opening too fast, or that the air cleaner is not supplying sufficient warm air during the post choke but not fully warmed up scenario. It is als very possible that the primary power piston is sticking, causing a lean condition as the vacuum drops. This condition is VERY common with Q-jets, even those recently "overhauled." One other condition is the missing or leaking check ball in the accel pump circuit, or a defective accel pump. Be sure also that the ignition is A-1, as a defective plug wire or fouled plug can cause a backfire. Several things to check, but be sure of the ignition before even considering the carb as the culprit. Test twice and replace once. Too often I have seen problems created while trying to solve a problem. Ray
