I have the option to purchase what is described as a reconditioned Quadrajet 800 cfm that was on a Chev 454 but numbers come back to a 1978 Oldsmobile 350 - 403. #17058253 (Price is $600-700 nzd / USD $375 - 440) Is this a good start for a 66 425 with a factory quadrajet manifold. Good quadrajet carbs are hard to find down here in NZ. I understand it may need rejetting / calibrating and possibly another throttle linkage to clear the intake and different base plate? Or am I better just getting one built and shipped from the USA to suit the engine application. Any advice, information or experience in updating a 66 Q-jet on a Nailhead much appreciated. Thanks
A red flag always pops up when I read 'reconditioned' when it comes to Quadrajets. Way to many examples of these out there that are lipstick on a pig. If I didnt like doing these myself, there are only a few I would trust to buy one done from. If you are set on getting someone to put a good one together for you, Tech8 or Cliff R on here(might be a few more I am not aware of) would be good options. would guess when the day gets rolling over here that either one may chime in. Not positive on that intake, but there may be some different mount gaskets you may need to accomplish what you are after when using the late model carbs. If you like tackling these on your own, both these guys I mentioned have books that will help you with the mods needed. Even if you had one built they really help with the tuning process also. I only have experience with Cliffs stuff, always good parts and very helpful with putting together a custom kit and suggestions on mods. Of course that is if you can find a good core. Good luck.
Thats a later model q-jet, i would try to find an earlier unit. I know the 66 425 q-jets had a side inlet fuel line. Sometimes this is a requirement due to interference issues. I would make sure thats not an issue before you buy anything. The correct 425 q-jet will be tough to find. I seem to think that there was some sort of mid-year recall or major revision on that carb anyway. I would suggest finding a 67-69 400 or 430 carb and then ordering the jets and rods that the 425 would have came with. The idle circuit will probably be close enough with the stock engine.
Thars a great carb to start with , my only concern is making sure you have a reasonable provision for a throttle return spring. The later M4M carbs are a good choice for a spread bore nailhead manifold because the high idle linkage is wide enough that it doesnt interfere with the heat trough casting of the carb pad. Yes it will take some recalibration but not much, and nothing crazily complicated. I run a later front inlet Q-Jet on my 65 401, works great and loves the 800 CFM and the provision for a hot air choke.
I am in exactly the same predicament as you. Using a 1966 manifold, but finding the correct carb here is almost impossible like in NZ I found a later 800CFM carb at a swap meet and with Cliff's help and expertise will be setting it up to run. Have a look at the thread I started " which ports to use " and read through it. You will be able to do the things Cliff suggested if you decide to go with a later unit. Good luck with whatever direction you take.
Thanks Rhett for the information, picture and advice, great to know it is all possible, and the linkages will clear.
Cheers Ken, found your posts yesterday and have been checking them out. Will continue to follow with interest.
Thanks Joe for the reply. I know Ken from Everyday Performance has the 66 style carb every so often but they need modifying (which he does) to eliminate the problems. I had an email from him a few years back which I have lost regarding a good core to start with but think it was an early 70's Buick carb. As mentioned, any quadrajet carbs in okay condition are rare down here. I have a squarebore manifold also which I will purchase an AVS2 for but would like to try the quadrajet as well. No hurry, engine not built yet but this 800 surfaced on an auction site so I just wondered again.
Thanks Ken, not sure which path to go down yet but thanks for the clarification. What difference / advantage is thereby adapting the Nailhead linkage to the later carb vs using the later linkage? Its going into a 56 Special so nothing will be original.
I wouldn't touch a 1965-66 Q-jet with a 200' pole.....JUNK compared to the 17058253 carburetor. Those POS are what gave ALL Q-jets an undeserved BAD reputation as a good reliable high performance unit. To this day I still see uneducated "guru's" regurgitation all sorts of inaccurate information about Q-jets just because those early units had so many fundamental problems. To be perfectly honest I wouldn't mess with a 67-68 either. They just have too many "issues" and still used the early poorly located hinge pin and huge float set-up. Plus ALL of them will leak at the bottom plugs and many of those early castings leak at most of the other driven in lead plugs as well. The 17058253 is a far superior unit in every respect. Big CFM, APT, latest design hinge pin/float set-up (they will take 7-8 psi without a grumble), they convert easily to electric choke, far superior fully adjustable choke pull-off arrangement and pressed-in/swaged bottom plug (rare to see one leak even though every idiot who needs to get off the Forums and go back to his day job will tell you to smear a ton of JB Weld over the bottom plugs). I use and prefer 1976 and later Q-jets for high performance work and retro-fitting onto older applications, especially when changes are made to the engine where an electric choke is needed. The 17058253 really doesn't need a lot of help to be a really nice performance unit. A slight recalibration, some high performance parts, quick-release pull-off, e-choke conversion and good to go. As mentioned you may need to modify the throttle arm for some set-ups.........
In Rhetts case it was necessary because he was installing in his 65 Buick with switch pitch transmission. In your case, the 56 Chevy, the original throttle arm may work fine. If you arent using the switch pitch trans.
Thanks Cliff, great advice much appreciated !! Since emailing the seller I have found out- "the following work was carried out by a professional carb specialist with a life time of experience, strip and clean, machine fit bushes, electro plate steel, fit service rebuild kit , fit electric choke and bench test" hasn't had fuel through it, so hopefully a good start and doesn't sound like a backyard build. Apparently he has receipts to back it up. Looks like I have a couple of Quadrajet books to buy and study.
Ken I am using a switch pitch trans in the 56 Buick so will take the gamble and modify / replace the throttle arm as required.
"Since emailing the seller I have found out- "the following work was carried out by a professional carb specialist with a life time of experience, strip and clean, machine fit bushes, electro plate steel, fit service rebuild kit , fit electric choke and bench test" hasn't had fuel through it, so hopefully a good start and doesn't sound like a backyard build. Apparently he has receipts to back it up." I wouldn't put much faith in all that. I get BOAT LOADS of carburetors sent here with fresh "rebuilds" and "restorations". Most come from shops specializing in them and I still find LOTS of issues starting with using crappy "blue" accl pump seals in them and tiny N/S assemblies that wouldn't feed a stock 305 SBC let alone the larger CID "high performance" engine it was built for. As mentioned previously the 17058253 wouldn't need a lot of help but stock it's really lean at idle and part throttle. You also mentioned it was being used on a big block Chevy and now is up for sale. Why is it for sale? If done correctly for the big block NOTHING out there will work better anyplace, dyno, street or at the track........some things to ponder on........
More great info thanks Cliff. No doubt all the good parts can still be purchased from you? Prior to it being rebuilt it was apparently on a 454 Chev, the owner has since replaced this with twin fours on a tunnel ram manifold. The auction closed with it unsold, so watching again.
