I have been running my 76 caddy quad (17056230) for about 9 months now and it has been great. For the past several weeks, it has a stumble from take-off when I give brisk throttle (about 3000) on the primaries. It runs great if I accelerate easy or very hard on the secondaries. The intermittent is similar to to car bucking from a bad driver on a stick. I checked the float and then quickly cleaned the carb. I also checked the power piston and it seems ok. I tried my friends carb (same exact carb # set up the same way) and it runs just like mine used to. I am certain it is the carb, any ideas? I was thinking of some trash in the carb somehow. Does that sound stupid? Thanks......
It sounds like it is just about when the secondaries are starting to open. If that is true, it could be the vacuum holdoff can on the passenger front for the back barrel flaps. Or it could be a maladjusted spring for tension on the rear barrel flaps. If vacuum pulloff is bad, they back barrels will flop open and bog. Same with too little tension in the spring. Those would be the first two places I'd look. Next, I'd check the linkage for the secondaries on the driver side. It should be smooth and progressive. Compare it to your buddies. Hope that helps.
Took it apart again and cleaned out. I cant find anything wrong with the carb and it still acts stupid. The only thing I found the first time I disassembled it was that the epoxy that we used on the plugs was rubbery and I think some of it went into the bowl. I don't know what to think at this time. Maybe it is a cracked casting that I can't see? My buddy here tends to think that we need to jet the carb down. I just think since it ran great for months-and-months that this would add another variable to the equation.
So I ran the car with no air cleaner and it was fine. I tried two other filters and it stumbled. I then tried another air filter base and then the original Buick ram air base. Still the same result. With the air cleaner off it is getting more air? Could there be an obstruction in an air bleed? Where should I look? I know we used "gas resistant" epoxy on the pressed in plugs and when I originally took it apart the epoxy turned black and some was missing.
Air cleaner lid too close to the carb will induce problems. I tried a taller RPM intake a few years ago, which required a shorter filter element, moving the lid closer to the carb. This induced a hesitation/stumble/bog that would NOT tune out.....Cliff
Thanks Cliff, but would that be something that can suddenly appear after running fine for 3/4 of a year. COuld the temp maybe induce it?
Difficult to say. I would replace the accelerator pump, re-seat the check ball, and new secondary plastic cam/spring at a minimum, as all these items are related to where you are having issues.....Cliff
I had a similar issue. Tore my hair out looking for it. Turns out it was the sock in the tank that had collapsed. I managed to track it down by running a garden hose to a gerry can to the fuel pump. Car ran good, so I knew it was in the tank. Pull the sock. Car runs wonderfully.
after trying three carbs I went back to the holley that was sitting on my shelf. It ran fine and no problems. The only commonality with the three Quads was the base gasket and the in-line filter. I am running the holley with no filter (temporary). Can a filter make the carb stumble? I discovered that it only stumbles when the car is full hot. This is weird. I want to check all the things that Cliff suggested, but three carbs seems like it is a Quadrajet issue with my car. Maybe I will wait until the temp is lower like in October and run the Quad?
Did every one of those Q-Jets use the same air cleaner housing that was removed, and the problem did not exist with the air cleaner housing off? Look at the housing. Also, make sure that the carburetor pre-heat valve on the air cleaner inlet isn't stuck shut. What is different between three Q-Jets and the Holley? Running well when hard on the throttle eliminates insufficient fuel delivery. It also eliminates the secondary air valve as a culprit. Does it crap out after some amount of full throttle driving?
You mentioned that when you had the q-jet on the car and you removed air cleaner the car ran fine. With air cleaner in place it would start to hesitate when hot. I have seen this problem many times and i would recommend checking the Tac door on the air cleaner it is probably stuck in the hot air mode and not switching to allow fresh air into intake when car is warmed up. hope this helps
I used an open air cleaner and the original Buick air cleaner with several different air filters. They both performed the same. This is just a mystery. I tried both my friend's and my carbs (same carbs from 76 Caddy's) and they acted the same. I then took the carb off his GS and put it on my car and it worked fine. This carb was from a 77 Caddy. They were all built pretty much the same. He tried my carb on his GS and it acted just like it did on mine. We can't pin point this issue. At this point I just want to know why. I've had it apart like 6 times now!! I want to try one on those filter tops next to see what it will do...
