Long time lurker 1st post. I'm restoring a 1971 Buick Estate wagon. The car idles great but suffers from what appears to be quadrabog. Here is the problem. I installed the heads last week and the car ran great for about 50 miles. It ran great power with the new heads was noticibly improved. It starts instantaneously. Idles great with 15" vacuum- needle steady. While driving in a rainstorm, the car lost power. It runs fine on the idle and primary circuit. As soon as the secondaries open it bogs. It will not exceed 2500 rpms and it falls on its face about 1700 rpms. It seems to run a little better with the secondaries disconnected but still lacks power. Engine has stock crank, rods and pistons. Cam is Crane 260 H. Heads are 1970 69 cc heads that are fresh from local machine shop. Ignition is stock distributor with crane xri with fireball coil new 45 delco plugs and wires. max timing is 32 degrees in by about 3000 rpms. Ignition is set at 6 d btdc. I disconnected the crane vacuum advance just to rule it out as a source of problem. I have checked the coil. It tests within specs. Tried swapping it out for another - no effect. stock fuel pump and rebuilt quadrajet (with parts and advice from Cliff Ruggles). Ig New fuel pump. I have pulled the carb, cleaned it, reset the airflap to closed plus 1/2 turn per factory manual. All tubes in the carb are in place. The accelerator pump gives a strong squirt in both primaries. There are no apparent vacuum leaks. Choke is not sticking. I've tried making the APT richer and leaner- no major effect on power. I have pulled the plugs and replaced them with new 45 Delcos. The even bank had sooty plugs on cylinders 2,6 and 8. All other plugs were normal. I had trouble sealing the valve cover gasket on this bank. It is now sealed. I have checked engine grounds. They are tight and clean. Car has a 94 amp 12si alternator that puts out plenty of power. Battery is optima yellow top. I'm stumped. Other than swapping out the Crane xri for points. What have I missed? All thoughts appreciated. Mike Update- fuel pressure is at 7-7.5 psi. I blew out the fuel line. replaced cap and rotor- still wont rev past 2000. I even checked for dragging brakes. Going to buy fresh points and swap them in for the crane ignition module!
The only thing you didn't mention is the primary vacuum break on the Q-jet. It has a link to the secondary air valves that prevents them from flopping in too fast. Make sure that vacuum break is functional. I would also check fuel pressure when you experience the problem. The pick up in the tank may be clogged now. That might explain why it was fine for 50 miles.
Sounds like you may have fuel delivery issues to the carb. Like Larry said, could be sock in tank, fuel pump, fuel filter, cracks in fuel line causing air suction, non vented gas cap, fuel filter too low. I would be glad to email you my Quadrajet tuning sheet if you send me your email address. Sounds like you got a handle on that but maybe it has something helpful.
Thank you for your feedback. I haven't been able to test fuel pressure with the steel line. I'll try to track down some fittings. The primary vacuum break works. That and air flap were first things I checked. I guess I will try blowing out fuel line and placing a piece of clear hose in for testing purposes to see if there is a blockage or air leaking. Tank is relatively new, sender is original. To my knowledge all steel lines are original but they appear rust free. Rubber hoses are 3 years old.
Thanks! I'd love a copy of your tuning sheet. Never know when you'll pick up a new trick. mkeller@kellerls.com
Tee in a fuel pressure gauge. See what the fuel pressure is doing when you experience the problem. You can just use a piece of 3/8 fuel line from pump to carburetor (temporarily) and tee in a pressure gauge. Tape it the windshield so you can easily see it.
Make sure mechanical advance is not sticking and operating properly, then cross that off the list. Larry
It is a long shot, but possible that one of the secondary feed tubes inside the carb has fallen out of its mount. Those tubes are pressed in, and if one comes out, the bog from the secondaries opening will be impossible to stop. Also, unrelated to the bog, but isn't 7.5 lbs of pressure too high for a quadrajet?
No, just the early ones. Mine takes 9-10 psi without a problem. http://www.v8buick.com/showthread.p...acceleration&p=2088866&highlight=#post2088866
The mechanical advance works properly. The secondary tubes are intact and clear. I will remount my fuel pressure gauge and drive around with it on the windshield to see what it shows when the bog occurs. I'm also going to wire the coil to the battery to see if the issue is somewhere in the harness. The problem arose during a torrential rainstorm after driving through deep water in the streets.
You said the car ran fine until you drove thru deep water. When I bought my GS in '85 it still had original factory exhaust (duals) I had noticed the exhaust sounded different from the right tail pipe compared to the left. Later when I replaced the exhaust, the left head pipe inner layer was collapsed, I had NEVER seen such a thing. Apparently, the factory head pipes are laminated, meaning they have an inner pipe also, for some reason, it collapsed and was the size of a broom stick inside:eek2: Some said it can happen if you drive thru deep water, something with the sudden temp change, hot pipe being sprayed with cold watero No: Your head pipes original?
Excellent point Mark! I remember chasing our tails back in the early 80's with a little old ladies earlier Nova that had that issue. Spent 2 days, tried everything, finally found it. Wish the internet was around earlier for troubleshooting back then. Even if this not the OP issue it is good info to put out there. Larry
I appreciate all the replies. Just when I thought the possible issues were narrowed to fuel or ignition someone throws in exhaust. I don't notice any difference with the exhaust after running through the water. My pipes from the y pipe to the muffler are original. Is there a way to measure exhaust back pressure to rule this out? I still suspect a fuel problem. I had to drive the car 80 miles round trip into Miami yesterday and it runs great as long as I don't open the secondaries. On the primaries it will gradually accelerate to 2500-2700 rpms (about 65-75mph) It does run hotter at 70 than it did previously but no lean surge. I have a dash installed vacuum gauge that I have been using for tuning. Once vacuum drops below about 7 it starts to stumble. 5 or less and it has no power at all. I wont get a chance to do any more troubleshooting until Monday.
If the Y-Pipe is aftermarket I would disconnect the attaching OEM pipe. May want to do this during the waking hours. Tha Nova we worked on sounded totally normal to us, but inner pipe was collapsed a bit more than 3/4 of the total diameter.... same symptoms. It's worth ruling out. Larry
In Park, note the vacuum reading at idle. Then rev the engine to 1500- 2000 RPM and hold it steady. The vacuum should jump up a bit and then remain steady. If it starts to drop at that steady RPM, you have an exhaust restriction somewhere.
Fuel pressure is 5.5-7psi. 5.5 when floored at 2500 rpms. 6 at idle and 7 under mild load. So this appears to rule out fuel flow. Vacuum is 17 at 750 in neutral. When revved to 2500 in the driveway it rises to 20-21 and stays there. Although driving under load the vacuum seems lower than usual. have I ruled out an exhaust issue. Interestingly there is a buckle in the body of the muffler that was not there two weeks ago. car seems to be regaining some power but still bogs down about 2000 rpms. I'm going to readjust the secondary air door a little tighter again.
My initial gut feeling was the secondary air blade spring...possibly it doesn't have any tension on the blade. I bought a car and had the exact symptom you were having. I pulled the carb to rebuild it and found the spring was totally loose. I gave it some tension and tightened the set screw and it was fixed.
Dad and I rebuilt a 327 in a 1968 Impala last spring. When we went for a drive to "seat the rings", it seemed to run worse and have less power the greater the throttle opening. Checked everything and couldn't find anything and had us stumped, and so worried I had botched the rebuild, then eventually found a blue paper shop towel stuffed up the snorkel of the air cleaner. Maybe peek in yours to make sure it is open? Just an idea to check.
