I now have the parts to convert over my extra fuel line to a front-inlet, so I'll be mounting the 800 CFM Q-Jet I rebuilt last year in a little while. In the meantime, I acquired a second 800 CFM core...this one is a 7044240 model. I've just gotten it stripped down, and gotten all of the frozen parts ripped out of the bowl...idle tubes and all. There's a lot of crud inside...looks like instant oatmeal. Time for the chem dip bucket. The float, needle, seat, and accel pump is toast, and the power piston hanger came off...but maybe it can be re-attached. Can't read the size on the primary jets, but the primary rods are 49C with CT secondary rods. Secondary air-door cam is all melted, so I'll need to change that out, too. Just like my other 800 CFM, the primary shaft will be swapped out with a 1967 one in order to hook up the switch-pitch. Pics to follow.
Have fun. Jets should have been 73's I always replace the needle/seat, float, pump anyway. If you pulled the top out of the power piston, you can set it back in, but you need to check the height of the primary rods in the jets when you are done. It would be a good idea in this case to add the APT screw in the base plate so you can adjust that part throttle setting. Most of the cores I get these days are in similar condition, like they sat in bottom of a lake for a while. It's takes some scrubbing, but they can turn out nice. Make sure all of your passages are clear.
I have never seen an accelerator rod in the outer hole, that must be an early 74, the slanted bowl vent is nice. The 4MV must not be until 75
Yea, you want to move that accelerator pump rod to the inner hole. That crusty stuff is so common these days. Water gets inside and just sits. Good soaking and cleaning will get rid of it though.
I still have the A.I.R. in place. Factory documentation says outer hole on the pump arm if the A.I.R. is equipped on the engine. First soak of the '74 got some of the white crud out of the bowl, but there's still quite a bit left. I may need to soak it again, for a longer time. The power piston and hanger cleaned up well, so did the primary/secondary rods with a bit of polishing compound. Primary rods have what appears to be: "49C" stamped into them, secondary rods are: "CT." I'm thinking of using marine-tex to re-attach the hanger to the power piston. I still need to pull the secondary air door shaft in order to put a new cam on it, and the primary throttle bushings and shaft need to be replaced. I have another spare throttle shaft from a 7027248 core which has the correct switch-pitch linkage, that one will replace the stock shaft.
Whats the letter on your hanger? and whatever system you have that requires you to use the outer hole , If I had it I would get rid of it and use the inner hole.
I've soaked the carb body 2 more times: once more in the chem dip and then in hot water with TSP. The crud is eventually going away, but it sure is tenacious. Gonna take off the secondary air doors next...need to put a cam on there. After that, the primary throttle bushings go in, and then the 67 shaft with the switch-pitch linkage. The main jets in the carb look like 75s....though they *could* be 73s. Even after soaking/polishing them...the numbers are hard to make out.
Those castings needs to be bead blasted and zinc/chromated. It's nearly impossible to remove all the corrosion with any type of chemicals, and when it does the casting is left unprotected. I'd replace the jets and metering rods as well, new PP spring, and secondary cam/spring. The pump shown in the picture is not correct for the carburetor, they didn't use a rubber boot or pump cut for one, so it's probably an early style pump from a "generic" kit. I'd install the later style pump which is a big upgrade for those carburetors. The power piston hanger can be re-installed an crimped in place. The arms may be bent or uneven, they need to be level and exactly even as those carbs as the metering rods are tapered and they are tuned with the APT system in the baseplate......Cliff
You're right...the boot is not original. Neither is that primary linkage...this is a sort of Frankencarb I've assembled to get the benefits of 800CFM without losing my original hookup to the switch-pitch. I put that pump in with the boot since the length was the same as the original, and the boot helps to keep dust & other crap out of the bowl. If it turns out the pump doesn't work properly, I can always swap it out...it is a reversible modification. The parts are all from Craig's shop...no generic stuff here. If I can't get the crud cleaned out, I may bring to a shop for blasting & re-plating. I may take it to the local shop who did my valve covers...they handle small piece work like this as well.
CLR does a decent job on the white crud, but you have to watch the dip times because it can darken the casting. Sometimes that white oxidation seems hard as a diamond. hard to get off there.
Lemmy - I get the whole frankencarb thing, I actually built one myself out of a 67 baseplate and a 73 body and top. I was using it for alternate race carb, but wanted to get my hot air choke back - so here's another angle - I wanted to use a 76+ 4M4C APT carb (17059247) in my 65 SP car, but didn't want to lose the linkage too. TechG8 (Ken) had the idea, and was able to cobble together the 66 throttle linkage on the 4M4 throttle shaft and viola, the best of both worlds. I actually had Ken plate the body as well and just got this carb dialed in. Might just be the best I ever built, and by far the prettiest. And being 800 CFM we'll see this fall if it's a runner at least in comparison to my 66 750 CFM carb.
Wow...looks great. Nice & shiny. I only had one other 4MV carb which looked that nice...too bad it never ran well. The 4MV I have on the vehicle now has the primary linkage attached to the shaft via screws. The previous owner drilled out the 3 rivets and replaced them with screws, so that they could use the linkage for a Chevy engine. Lucky for me, they included the old Buick linkage as well, so all I had to do was unscrew the Chevy part and put the Buick one back in. I thought about using the entire base plate, but I was worried that the channels wouldn't line up correctly with the carb body. I ended up just changing the entire primary shaft out when I did the bushing fix.
There probably would be differences between baseplates, although my 67 baseplate and 73 body are perfectly happy together. However, there are big differences between 66-74 carbs and later models. As far as the baseplate is concerned, the throttle shaft on earlier models is to short to use in a later base. That's why we had to cobble together the linkage, using basically the same process you used on your carb. One other thing to be mindful of is that the later carbs seem to have some interference (at least on nailhead manifolds) with the heat passages cast into the plenum at the fast idle cam. This may not be an issue with the flatter BBB manifolds. I got around that by using a 1/2 spacer.
Well i didnt do any welding in that pic, The picture was an after thought. It basically shows what can be done with a 4MV, Electric choke, plastic choke pull off with port easy to drill. some epoxy filller so both sides look like they would have same airflow pattern. I need to move the pcv to the front though.
