Hey guys, Just bought a 72' 455 for my 1972 GS. Dad's building the motor and I was thinking about trying to rebuild the carb, If anyone has any experience in doing this that would be great. I have a pretty go understanding of what I need to do but any insight or thanks to watch for, or exact directions would be really helpful haha.
Most the instructions will be in the rebuild kit. The main thing on a q-jet is to make sure the top plate and the body are not warped. Most of them are over tightened mounting them to the manifold, thus bowing/warping them. If warped they usally leak vacumn, sometimes you can get away with a thicker to gasket. Then there are the fuel well plugs on the bottom, most of them leak fuel. I have found they dont leak till they get hot from the heat of the engine. I drill them out, tap the holes, use a threaded plug coated with epoxy screw them in snug, no more leaks. Some coat with JB Weld or epoxy, but this is not a good fix in my book. There are special blue colored plungers designed for ethanoil gas, suppose to not break down, I have used them and the old one and they both work OK for me, personal preference. Of course make sure you adjust the float, mixture screws 2 turns out to start, adjust with vac gauge while eng running. Get a book and read before you do it. Also make sure the primary throttle bushings are not worn, they will leak vacalso, you may have to drill them out and press in new ones. Then there is the coke set-up divorced or non, choke needs to be accurate, and your choke pull off vac canister, most the time they need to be replaced, use mighty vac to check it. Research it, if you have questions ask, I rebuild them all the time.
If you decide to put throttle shaft bushings in the baseplate (I would), remember.... BEFORE you go to remove the screws that hold the throttle plates in, you must grind off the "staked" or "mushroomed" ends of the screws so they will screw right out without breaking off in the throttle shaft.
I would replace the idle pickup tubes as well. The first go around with my carb I thought I could get away with cleaning them with welding wire. I thought I did a pretty good job between the wire and liberal amounts of cleaner. Then around the third time I took it apart I decided to replace the tubes anyhow. Upon inspection after removal there was still a thick coating of varnish clogging up a very precise hole. Easier just to replace while the carbs apart.
To add to some of the good advice here, I recommend replacing the cam and spring on the secondary air valve shaft. The cams often become worn or cracked, and the springs become weak, and make proper tuning nearly impossible. If you intend to modify the engine (higher compression, larger camshaft, etc.) the carb may benefit from a modified idle circuit. There are many good tips for doing this in the books by Ruggles and Rowe, I recommend you read them. Any modifications in the primary metering circuit should be approached with caution. Every change in primary fuel metering jets and rods alters the air/fuel ratio, where often times factory metering is close to optimum. Pay close attention to the well in the main casting where the check ball seats. If fuel leaks around this check ball, accelerator pump function will be compromised, and will result in an off-idle stumble. This does not happen often, but does happen. There are many small orifices in the castings that need to be free of obstruction for proper carb operation. These often times do not need to be enlarged, but they must be, and I stress, CLEAN CLEAN CLEAN. Good luck with your re-build.
Does anyone happen to have a sheet over how these quadra jets go back together. I got an assembly sheet that came with my rebuild kit, but this kit is must be for more than 1 set up because certain parts on the sheet are for different set ups.
Matt. Here is a generic exploded view. This is not specific to any year or application, but will give you a general idea of how they are assembled.
see i have the exact same one, but Im confused over how part 47 and part 48 go back together and its driving me nuts haha
Part 47 is the fast idle cam, and part 48 is the cam follower...this part interacts with the fast-idle adjustment screw. Place the carb on its side, with the passenger side facing up. Slide the cam onto the choke linkage/pull-off (part 46) with the number on the cam facing outwards. Then slip the follower onto the rod, and drop it onto the passenger-side of the carb body. The choke arm (part 49) needs to fit into the choke linkage, so use a punch or screwdriver to line it up with the hole before inserting the choke parts.
Matt. I think I understand where you are having trouble. The carb in the pics is for a '70, but the '72 carbs use the same arrangement. Part #47 is the fast idle cam, and part #48 is the secondary lock-out arm. Pic #1 shows these parts on the side of the carb body with the vacuum break assembly removed, and how the parts interrelate. This is somewhat confusing because the secondary lock-out must mount outboard of the fast idle cam, but inboard of the remainder of the vacuum break assembly. Pic #2 shows the inboard side of the vacuum break assembly with the fast idle cam in place. Note that the actuating arm is below the cam. Also in place is part #49, which is the link to the rod that operates the choke valve (flaps). This link must be inserted into a well in the main body, and the shaft of the break assembly holds it in place when installed. Pic #3 shows the assembly from the top of the carb. All of this can get a little tricky to assemble, and sometimes you will wish you had a third hand. If you need any more pics, I will try to help.
