I've now assembled four complete quadrajets from 1967, all factory-correct for my 430 Wildcat. All have the new throttle bushings in the base plate, new floats, gaskets, check balls, and ethanol-resistant accelerator pump cups. There's the 7027241 carb currently on the engine now: ...and the other three on the bench, all set & ready to go: There's one more 7027241 unit with the older needle-seat design (non-plunger): The other two are 7027248 (late-67) models with the newer design needle-seat setup. This one also has the little guard tower around the choke linkage: The carb on the engine now is running well with 37 rods and 73 jets, but I think I can get some better performance with a few tweaks. I plan to try out the second 241 unit with 39 rods, then maybe try out the 248s one-by one. Let the hot-swapping begin!
It just took 17 years of owning this Buick, and scouring craigslist and evilbay for the parts. For the last carb pictured, it was a correct core, but the previous owner had swapped choke and throttle linkage to make it chevy-friendly. I went through my parts and took the base plate off my "Rembrandt" carb which didn't run right, and slapped it on. I also went through and swapped out linkages, vents, springs, rods, accelerator pumps, etc. to get these complete. I had to check out the spring & pump lengths, measure the rods -w- digital calipers, and make sure everything fit correctly. I still have a 7027248 body which needs to be heli-coiled at the fuel inlet, but if I get around to it, I can end up with five of these suckers to play with. For now, I think four is plenty for me to tinker on & get things running right.
Looking Good.... Keep us posted with your results... I'm currently running the 248 model at the stock settings on my 425...
Thinking on it, I recall the stock power piston spring being a bit longer on the later model. There's a whole nother level of tunabilty x 4 Is that an adjustable air bleed screw on top of the 241 ?
Yes, both of the 241 carbs have the air bleed screw under that little triangular cover on the bowl vent. I tried opening it 1/4 to 1/2 turn, and it made the engine run choppy & miss at idle. There didn't seem to be any setting which helped the idle. I closed it all the way, and the idle smoothed out. Maybe it's good for carbs with huge main jets and tiny rods. The 248s got rid of the bleed screw.
"Yes, both of the 241 carbs have the air bleed screw under that little triangular cover on the bowl vent. I tried opening it 1/4 to 1/2 turn, and it made the engine run choppy & miss at idle. There didn't seem to be any setting which helped the idle. I closed it all the way, and the idle smoothed out. Maybe it's good for carbs with huge main jets and tiny rods." Prior to 1970 the airbleed screw (when used) led to passages under the idle airbleeds in the airhorn. This will effect the idle fuel delivery at any particular engine vacuum. When you open up the screw, the draw on the idle tube is diverted to the air bleed instead, so it can have a dramatic effect on idle fuel to the engine. Starting in 1970 on Pontiac carburetors, and used thru 1974, the airbleed leads to passages under the main airbleeds, so idle is not effected in any way, just main metering......Cliff
Thanks, Cliff. I wondered where the air was going...obviously it was leaning out the idle when I had the screw open. Now, I have a clearer understanding. Your book, parts, and posts have been instrumental in my figuring out how to keep this machine rolling. Same goes for all the rest of the people with their helpful posts on this board. It's a fountain of knowledge up here.
Thanks. It will have a very slight effect on main fuel right off idle, as the idle system does continue to feed the engine as the throttle opens via the idle transfer slots and lower idle airbleeds. It's best in all cases to gently seat that screw, this will be the richest setting, and only open it if you don't have control of idle A/F with the mixture screws.....Cliff
I've considered that, too...but all of my GM service docs instruct that since this is a A.I.R. engine package, the pump rod belongs in the outer hole on the arm. I'll give it a try...the present 241 carb has a slight stumble off-idle until the engine is completely warm.
Another interesting difference between these 4 carbs is the secondary rod selection. Here's what's in each: 7027241 on car: AY 7027241 on bench: AY 7027248 #1: AU 7027248 #2: AZ I have the books which list the dimensions of each rod, but there are so many tapers to the tips, it's hard to ascertain which rods are the richest/leanest.
Okay, I've taken off the nice-looking 7027241 and replaced it with the 7027241 which was on the bench. This'll be its first run with the new bushings. The nice-looking one was run for a few months, and did well. Once warm, it idled fine and had reasonable zip around town and on the freeway. No leaks, but an occasional off-idle stumble and cold starts were sometimes rough. I looked at the fast-idle cam, and it looked like the teeth were slightly rounded-off. The fast-idle cam follower on the primary throttle shaft had a lot of play, and was pretty wobbly. The follower was only hitting the cam teeth on edge, and was slipping off. I've seen some base plates with a thin nylon washer in-between the follower and the baseplate to keep the follower on-axis. Anyway, I'm going to change out the cam and install a nylon washer to reduce the play on the follower. I'll also check the rest of it out to see if any of the well-plugs were leaking, etc. Tomorrow, I'll fire up the 430 with the new carb and see how it flies!
OK, I had the first 241 carb on for about a week. Seemed to run fine...with a little more pull off the line & some more top end. The throttle linkage was a bit tight, as they usually are with the new bushings, but it loosened up after a few days. Then the fuel inlet started to seep again. I checked the inlet nut, and it looked like my heli-coil repair was beginning to pull out. I removed the carb, and replaced it with the 248 unit which had the tower around the choke linkage. I checked the 241 heli-coil job, and it was, indeed, beginning to pull from the newly cut threads. I was using a fuel inlet nut with only about 1/4" of thread, and only 1-2 turns of the inlet were engaging the heli-coil. I replaced the insert with a fresh one from the heli-coil kit, and used an inlet nut with about 1 full inch of thread. This way, all 4-5 turns of the heli-coil insert are engaged, and there's less chance of them pulling out. I've installed a new gasket as well, and the fitting looks flush and tight. Meanwhile, the 248 carb is now adjusted and running well. The tower was rubbing against the choke linkage, but I've bent the side of the tower so that it clears now. This carb runs even better than the 241s...no stumble at all and plenty of pull & top end. Maybe that new needle/seat system allows the bowl to fill faster so that the fuel level stays higher. I'm still tinkering with it, but I like how it's running so far. This carb has 39 rods and 73 main jets.
I've now had the first 248 unit on the engine for a few weeks, and it seems to be running the best out of the three I've tried so far. The inlet nut gasket was giving me trouble at first, but I've changed out the inlet nut to one of the more narrow styles, and the gasket mates to the fuel inlet on the carburetor body much better. No leakage or seeping of fuel is observed. This carburetor was one of the rattiest cores I've ever seen. It was obviously on an engine stored outdoors without any hood over it for a while. The throttle blades were completely frozen, and the bores were full of mud, weeds, dead bugs, etc. Once I'd gotten the screws moving (lots of solvent & and impact screwdriver) and took the air-horn off, the fuel bowl was actually pretty clean. No gunk had gotten inside to foul the jets and pump passages. The fuel inlet threads were also intact. I used the baseplate and linkage from my Rembrandt 241 carb with the warped air-horn, and soaked/cleaned out the rest of the ratty 248 to put it all together. I also used the choke and fast-idle cam pieces from the Rembrandt. This carb takes a little while to warm up (need to adjust choke rod to kick the fast-idle up one more step), but once warm, my idle is very smooth. Absolutely no stumble off-idle, and it pulls very smoothly through the gears. I occasionally hear a little burble thru the exhaust, maybe the mixture is a tad on the lean side, but otherwise this carb is running great. I'll post pics soon.
Here's a photo of the ratty 248 with Rembrandt baseplate in action: I'm thinking of trying out a 1971/1972 4MV unit which was used on the Cadillac 472/501...those look pretty compatible with my 430 setup.
One thing to watch for using the 70s qjets on a 430 - the baseplates are a bit different. 430 carbs had the early, wide baseplate and the 70s carbs generally had a slightly narrower configuration at the primary throttle shaft. This can lead to interference on the cast 430 intakes with the big "smiley" channel in front of the primaries. Its the choke cam follower and screw that interfere with the intake.. Check it out youll see what I mean. Maybe you could grind some of the intake if you chose, or run a spacer or go without the choke cam follower etc. Ask how I know about this..... Now maybe the Caddy unit has the right baseplate for you, I dont know, but I thought Id mention it as something to be aware of.
Thanks for the info. I was only considering it because the 1970 and later models have the improved float fulcrum point in them, and the caddy is a side-inlet model with the divorced choke just like my 430 uses. I planned to swap baseplates, as long as all the passages line up correctly, but if they don't I can scratch that idea. The 248 on the engine now still had a little bit of seepage at the inlet gasket. I decided to take the inlet off, and polish the pot metal near the threads which mates with the gasket. I used my dremel tool with the polishing attachment. I also changed out the nylon washer on the inlet nut with a steel one, and use two gaskets to improve the seal. The seepage is virtually gone now.
Another update on the ratty 248 Q-Jet after a few more weeks of touring around town: The seepage started to come back on the fuel inlet, this time in-between the 2 gaskets I was using. I decided to seal off the gasket surface with some Permatex aviation form-a-gasket between the inlet body and a single gasket, and use a metal washer from one of my older carb kits between the gasket and inlet nut. Seepage stopped...hopefully for good this time. I need to change this thread to Quintet...since I've just received another 248 core off of evilbay. This new 248 is in very good shape, and I got it for $55, shipping included. It's got everything intact, except the secondary lock-out arm, and I have plenty of those to spare. No real rust or seized parts, it is cleaning up very well. Inside, it was stocked with: mains: 70 primary rods: 37 secondary rods: AY I had to soak the power piston in solvent & tap it out with a punch from underneath, but it came out after only a couple light taps with the trim hammer. The spring is still stuck in the bore, gonna let it sit in solvent for a while. This core looks really clean, I think it's going to go back together easily and run sweet. It has one of those self-tapping inlet nuts, but the threads still seem to be okay. The base plate is missing the AIR fitting in the back, but I have another AIR base plate with fresh bushings which I can use instead of this one. Gotta leak-test the well plugs after soaking the carb body, too.
