I’m looking for suggestions for parts to tune my carb. I have a restored, restamp 7040256 that is set up close to what that carb should be. The problem is, it is a four speed w30 setup so it does not have primary metering rods or a power piston, BE secondary rods and .058 jets. I’m using an automatic transmission and stock bottom end 10.25:1 68 455. I was thinking of adding primary rods and a power piston and possible changing the secondary rods and jets to match a 7040258 which would be adding the power piston and 52c primary rods, AU secondary rods and .069 jets. Would 7040251 parts work better with my combo? Maybe another combo somebody could suggest, as well as a place where these parts can be found.

 

What camshaft does this engine have? That will make a difference on jetting.

 

Thanks for the info, that’s good to know. It still has the factory cam, as well as pistons and the small valve C heads which have never even been removed from the block. Unfortunately wild about cars removed their service manual section so I can’t check the cam specs. I believe all 68 455 motors received the same cam but my motor is the L66b which is the high compression 2bbl. I’m pretty sure it’s not going to be as aggressive as the 70 w30 four speed cam though, so it’s probably a good idea that I do make some changes. Since I don’t need anything with a specific number I would probably just look for a different carb but this one is beautifully restored, I bought it for a great price and it’s an obvious restamp.

 

OK, for whatever reason I didn't see that you have a basically factory 68 455 engine.

Here's the carb info I have:

Year & Application.....Carb #........Main Jet.....Primary Rod.............Secondary Rod
1968-
400/455...................7028251.....7031971......703 4849- "49B"...........7033655- "AU"

1970-
455 W-30 M.T............7040256......7002658..........NA... .................7033655- "AU"
455 W-30 A.T............7040258......7031969.....7040701- "52C"......7033655- "AU"

 

Awesome, thanks again for the info. Do you have a part number for the power piston? Any opinion on the “BE” secondary rods vs the “AU”? I only ask because I’m having a hard time finding the “AU” rods. I have not ran the carb yet but the person I bought it from said it ran good with it’s current setup. If I could just add the power piston and primary rods and change the jets would everything still work together?

 

Yeah, I think you could get it to run OK by changing the jets and adding primary metering rods.

Below is the data I have for those secondary rods. There's also this web site with a listing of all the rods.
http://www.hioutput.com/tech/qjetrod.html

Note the tip length difference between the two. The web site above explains it.

I.D. Code...0 deg...20 deg...40 deg...60 deg...70 deg...80 deg...90 deg...Tip Length..GM Part #
BE...........1329.....1311........1188.......1021. .....891........691.......410.......S..........703 4377
AU...........1345.....1291........1154.......927.. ......527........527.......527.......L..........70 33655

 

You can get a power piston from quadrajetparts.com or Ruggles if you need. It's the same part for an entire generation of carbs.

Now, the power piston *spring* changes, but you can just run what you got and see what happens.

That BE rod is MUCH leaner than the AU. You can also get rods and hangers at quadrajetparts.com (free plug, I buy a bunch of junk from them).

But get it running nicely on the primaries first.

 

Please ask quadrajetparts.com if the "flat" seat jets used in the Non W carb will work. The W carbs without the powervalve use the 2 barrel jets and have a 60 degree seat. I am very currious on if it will work. Curious minds want to know. lol

 

I’m a rookie when it comes to quadrajet carbs. Seeing as how this is a restamp and not an original W carb and I plan on adding the power valve, I would assume that the regular jets should fit. Right now I am just acquiring info, when I start acquiring parts I will be sure to verify that.

 

I’m not sure how accurate this is but according to FAQ, the same cam was used on pretty much all the standard duty 455 motors from 68-76. I have 10.25:1 pistons and small valve C heads, I also added an Edelbrock Performer manifold, headers and HEI. Should I still stick with the 7048251 specs or could I get better performance with a different year setup? I would love to be able to swap parts and be able to bolt this thing on and go without having to try different combos.

 

I’m going to say it just one more time, BUT A FRICKEN WIDEBAND AND QUIT GUESSING!!! CHRIST!

 

Thanks for the info. I have seen it suggested that a wideband is the best way to tune the carb. I figured that since my motor is basically stock that a stock setup would work well. I know the way the carb is setup right now will not be optimum, I’m just trying to figure out which stock setup to start with. If in stock form I am not happy with it and I have to tune it I will go with the wideband. I’m not going to be racing the car so don’t have, or want to buy a bunch of different jets, rods, or hangers.

 

Dude, that’s why you buy a wideband, so you don’t have to buy a shitload of jets and hangers that you don’t need!!!
Maybe this is a task better left to someone else. Just sayin.

 

I understood that, that why I said if I have to tune I would go with the wideband, so I don’t have to buy all that stuff. My point was since my motor is basically stock that a basically stock setup would be a good starting point. Hopefully since Oldsmobile put a lot of R&D in the performance of vehicles they designed I won’t have to tune it.

 

Sure whatever, good luck with that.

 

Maybe I’m dreaming, I just thought that if I put the carb back to the specs that match the motor that it would be good without tuning it. I’ll defer to you though since you have way more experience at this. You think I should go straight to tuning? So buy and install the wideband and run it as is? Should I install the power valve and primary rods first at minimum? Is there a good wideband you recommend that isn’t too expensive, hopefully I’m only going to be doing this once. As I said I’m still just gathering info now, and I am not opposed to farming the work out, or even selling my current carb and buying one that is already setup. I do have more time then money though.

 

Just a view on stock vs. wideband from a basically stock guy. I’ve got 2 66 big cars - not race cars. A 98 convertible and Starfire. Not hot rods, so “basically” stock motors too. Your starting point is totally reasonable, seemingly obviating the need for a wideband. Just go factory & be done. Simple, straightforward.

Problem is today’s gas is not as good in terms of octane, contains alcohol of some unknown %’age & blends vary across the year and season. On top of that, when someone rebuilt the engine they probably took some liberties, or made some tweaks that may make the factory set up less relevant. Different compression ratio, overbearing, head gasket thickness, cam, whatever.

I’ve built 15 or so qjets & recently came around to the need for a wideband, if only to avoid creating a giant tackle box of qjet parts, which I now have. I suspect @$200-300 a wideband O2 sensor may wind up cheaper than a box of qjet parts at $8-20 per set of jets & rods, hangers, rebuild kits, all that.

The bigger deal from a wideband is you get realtime feedback while you’re driving on what your car wants in terms of tuning from you. That’s huge.

I’m not a trained mechanic, so having technical feedback when the idle is right confirms my “feeling” that the engine is right. And when you’re at part throttle cruise, you can see if you’re rich or lean and that guides you to changing the power piston spring or APT height. And at WOT you get real, actionable guidance on whether to richer or leaner on rods and higher or lower hangers.

Point is wideband is a leap we think you’ll like. Yeah, you have to weld 02 sensor bungs into the exhuast and wire it up. The welding is a bit of a hassle, but the wiring is about as hard as a car stereo.

There’s a free alternative here too that you may like.

Years ago, I calculated out a giant set of combinations of jets/rods and secondary rods to try and zero in on the right combination for my engines. This was before the arrival of my wideband. It was helpful & you’re welcome to a copy of the excel workbook. Hit me privately with your email and I’ll be happy to shoot it over. It shows many factory combinations and has some notes on my big block experiments pre-wideband.

I hope this helps and please don’t be shy about the excel workbook. As I said it’s big, but has instructions, and has lots of Olds big and small block factory combinations. Same offer to any interested parties on the workbook. It’s a bit drinking out of a firehose, but may have details you’ll be interested in.

Cheers
Chris

 

Hey Chris, I appreciate all the info and the offer for the data. I will take you up on that when I need it. My motor hasn’t been rebuilt and the heads have never been off the block, I verified the factory high compression pistons with a borescope. I do see your point regarding today’s fuel being much different then it was in 1968 though. I think for now I am going to set it up as 7048251 by adding the power piston and primary rod, changing the secondary rod to “AU” and change the jet to 71, so it will at least run okay on my motor. Then come spring time when I have the car out I will dig into getting it dialed in. Any chance you have any of the parts I need in your tackle box of parts? Also what part of Northern California are you in? I’m in Modesto, but I do a fair amount of driving for my job.

 

Unrebuilt motor in 2020. That’s great. It says a lot about how these cars were built & used. One of the reasons I like the big cars is they lived cushy low-rpm lives relative to the Cutlass/442’s which were sold on the run-‘em-hard argument. You’re fortunate to have found an unmolested one.

If you’re building a 70-series qjet, I won’t have quite what you need parts wise. I might have a few odds & ends, but I’ve focused on the later 170-series carbs since they come in 800 CFM versions, came with electric chokes and have the adjustable part throttle screw.

I gave my long time mechanic all my 70 series stuff a few years back since he works on customer’s old cars and these parts are getting to be a pain to find. I wanted him to have it and it was great to get rid of parts I would only confuse with my correct 170-series parts. Qjet parts from the different series have a way of looking right and being wrong. Best to filter out parts I shouldn’t use.

I think you’re on the right track adding the power piston. It was a good design and allows you to really fine tune part throttle. Frankly I spend most of my time at idle and part throttle so getting it right is worth the time spend.

I suspect the high octane gas & cheapness of it in ‘68 contributed to no one much worrying about the finer points of qjets back then. You can cover a lot of carb sins with high octane fuel and timing. Just not possible anymore, unless you fuel up at Sears Point Raceway or your local airfield. What’s cool about the qjet is you can really fine tune it. That’s the elegant part to me, especially since it’s fully mechanical/analog, not digital.

The AU secondary rods are the go-to rods for high performance Olds. If it helps, I’m running a 73 and 74 jets and 48/49 primary rods in my 455’s. But my carbs are 800 CFM, not 750 like most 70-series, so there’s a delta there. 71 is well within the range of reasonable, then the question is whether it’s too lean. Which gets you back to either experience-based-feel or the wideband.

“Local” Parts sources:
Since you’re in Modesto & drive a lot, visit Turners Auto Parts off the 99 near Fresno. Great selection of old Olds and old GM stuff too. I’ll bet you’d find some cool stuff. I was down there last Fall and really enjoyed it. The owner, Jerry Turner, is 91 and knows every part in the yard. I wouldn’t call their prices cheap, but they’re fair. There’s also GM Sport Salvage in Stockton which is worth a visit, I have not seen their “new” location over there, but used to go see them when they were in San Jose. Decent guys from what I recall, fair prices, solid members of the old-car community. But it’s been a long time since I worked with them. If you go way up north to Red Bluff, there’s Hess Brothers who have a few old Old’s, but it’s been a year or 2 since I was there. The self service yards like Pick-A-Part and U-Pull-It have been pretty barren for mid-60’s Olds for 10 or 15 years now. I haven’t been in a few years and before that would go a few times a year, but was consistently disappointed. More or less the 60’s cars have been melted into toasters now.

My 2020 boneyard alternative is a saved EBay search. Here’s one for quadrajets: (quadrajet, qjet) -(chevy,chevrolet, camaro,corvette,chevelle) -marine, -ccc, -computer

I’m about 30 minutes north of SF. Not too many big Olds up here.

Cheers
Chris

 

I pulled the motor at Pick-Your-Part in Hayward about 20 years ago with the plan to rebuild it. It was in a totaled 68 Delta 88 4 door with shiny paint, really clean interior and 65k on the odometer. I assumed that meant 165, 265 or even 365k. The car had the cheapest tires you could buy but they were brand new, as well as a new alternator, starter and rebuilt 2bbl carb with the high compression orange air cleaner. I got the motor and long tail 400th for $200. I think somebody bought the car from the original owner then got it running before it was rear ended. I did a compression test and had between 180-190 psi in all cylinders. Pulled the manifold, oil pan and valve covers and it looked fresh and clean so I replaced the timing chain and oil pump and put it back together. I’ve put about 10k miles on it in the last 20 years in three different cars with an Edelbrock 1407.

 

Cool story. You had some good fortune there. Amazing how you can find great stuff in the boneyard. That’s a big part of the fun.

Sorry, didn’t mean to be treating you like a newbie, just wanted to be sure & share “local” resources. 20 years ago, that Pick A Part was useful. I wish they were that good these days. Have you been to one of the self service yards lately? Anything interesting?

My scores have been a bit smaller — power windows, cruise controls, power seats, that sort of thing. Nothing as good as a solid engine. But those scores were long, long ago. These days I’m in maintenance mode. Just cleaning, tweaking & tuning here & there.

Cheers
Chris

 

So I called Cliff Ruggles and talked with him for about 40 minutes. He said if I was going from say, a 251 to a 258 carb he could just get me a kit and I could just change some parts. Since the carb is a restamp and has been rebuilt we do not know the original application or exactly how it is set up now, he doesn’t recommend swapping parts. He said there are a couple of hundred things besides the jets, rods and hangers to set a carb up correctly. I think the wideband would help in tuning but at this point I need to get the carb setup correctly first. So my options are to send it to him and have him go through it or sell this carb and buy one that is already setup correctly.

 

Last time I talked to him, Cliff won't actually build carbs anymore (has no shop help) and he will only sell parts.

I was going to mention - if you're building a stock engine and using the carb for that exact application, and the carb core is virgin, then factory tune up will work pretty well. However, if it's been through a rebuilder with airhorn swaps, drilled air bleeds, etc, you have no idea what you have. The quadrajets had different air bleed hole sizes between makes (and changed within the same make over the years), which means a '68 carb rod/jet combo in a '72 carb won't perform the same as it will in a '68 carb. Hope that makes sense. If you want to spend some time, buy Cliff's book, micro drill bits, you can benchmark the carb you have and figure it out.

Honestly, your best bet is to buy a 7028251 (68 442 carb) or a 7040251 (70 455 carb) from someone like Custom Rebuilt Carburetors from New Jersey. Eric Jackson is also exceptional at Vintage Musclecar Parts. Their work is excellent, not the cheapest, and you'll be really close on the tuneup. You can put a wideband on to do any final tuning.

 

Hey Luke thanks for the recommendations on rebuilt carbs, that is still an option I’m considering. Cliff said the same thing you did about the air bleed holes being different between various years, makes and makes. Without knowing what it started out as and what was done to it during the rebuild, he can’t just suggest rods and jets for my application. He also said he is not rebuilding carbs right now because he has no shop help, however since my carb is already rebuilt he could go through it and set it up for my application but he won’t be able to get to it until the end of the year. I like your idea of buying his book and digging to figure out what I’m working with. Worst case scenario I get in over my head and either replace the carb or send it to Cliff so nothing would change, best case scenario with the book and a little tech support and parts from Cliff I could dial it in myself.

 

Here's a fun excerpt from a spreadsheet I did way back. It shows a bunch of factory big block qjet rod & jet combinations with associated factory seconadary rods:

Factory Olds V8 Rod & Jet combinations from the late 60's. These are some of the factory combinations

Hope you find some value in it.

Cheers
Chris

 

Chris, that's a neat spreadsheet, thanks for sharing. Were you able to capture which main air bleed size was used on each carb with that jetting combo? I'm not sure if Olds used the same size in all the airhorns through the years. That's the hard data to figure out... it would be nice if the rochester build data sheets were available for all these, I'd like to think they are out there somewhere...

 

Gang,
For anyone following, this table was written before I knew about the effect of air bleeds. It’s not inaccurate as far as I know, but it’s incomplete without the air bleed data. And wrap spring data & a bunch of other stuff. So, no, this spreadsheet does not have data on air bleeds. And yeah, it’s a missing variable.

All I can say is whatever factory was/is the best place to start, but I have no data on that. Cliff Ruggles & SMI have the knowledge on air bleed effects. If I recall correctly both Cliff Ruggles & SMI change the air bleeds in their “recipes” or “Stage 2” respectively, but I don’t recall quite what they do other than possibly enlarge them. I do not know what they do. Recently I read that certain changes in air bleeds are equivalent to a jet or 2, but I can’t recall the equation. Sorry.

I’m doing lambda tuning now & can react to a given set of air bleeds by changing jets & rods to achieve a desired lambda or AFR. Both of my street cars use 800 CFM SMI stage 2 rebuilt carbs and they work great, but I’m constantly tuning for that last little bit of precision.

Next, if I remember correctly, there may be data on Olds small blocks in the spreadsheet, but it’s filtered out here.

Anyone interested in the small block combinations? I’m not a small block owner but may have captured the data correctly. No warranties, etc, etc. but you’re welcome to what I’ve got.

Cheers
Chris

 

I have orders Cliffs book. My plan is to try to identify exactly what I have, and if everything is compatible I will build it to either 7048251 or 7040251 specs, then tune as needed from there. They both use the same power piston, spring, 49 primary rods, and AU secondary rods. The 8251 uses 71 jets and 0251 uses 70. Just did a quick search and I cant find the 7034903 power piston or the AU rods for sale new. I do have used CV rods in good shape. Most of the charts I can find list the specs identical. Should these be a good substitute? Is there a source for a new power piston, maybe a new part number that supersedes the one I have? Thanks again for everybody’s help.

 

Are you doing a period correct look? Personally, the later "Modified" Qjets with tge adjustable and the extra 50 cfm primary are the best carbs. Of course extensive idle circuit mods are needed. I am using a Canadian non CCC 83 307 Qjet which makes the late 70's carbs look like rich pigs in comparison on the idle circuits. Cliff has multiple recipes in his book as starting points.

 

My car is not original and more of a restomod/tribute so I don’t necessarily need period correct looks. The 1705 carbs would be close enough that most people would never know anyways. I actually have a 17057553 core off a 77 403, that’s where the CV rods came from. The main reason I would rather use this carb right now is because it is already restored and I bought it for a really good price. My long term plan may be to restore the 1705 and do a cam swap.

 

 

Other than the idle circuits, that 403 carb should not be too far off. I have a custom tuned 78 403 carb on the 350 in my 88 by Everyday Performance. The idle went from way lean to slightly rich with, idles much smoother.

 

Like I said the long term goal is to do the 1705 when I do a cam change, but it is a core and needs to be rebuilt and plated. The 70 series carb I have pictured above looks beautiful and has been rebuilt, so my short term plan is to figure out what it is and adjust to match my motor. I bought Cliffs book and joined his forum and with advice from here I’m confident I can get it to run good.

 

Yes, you can exchange CV and AU rods.
There's really only two power pistons - early (70 series) and late (170 series). quadrajetparts.com and others sell good used piston units. You won't find a new one.
The only reason to replace one is if it's actually damaged, like the tree got pulled out, or some jackass rebuilder cut the tip. You can replace just the plastic retention ring with a oversized split replacement unit.

Personally I find the 70 series carbs easier to work with, but that's mostly because I'm more familiar with them and have cannibalized something like 20 cores. Some, like Cliff, really like the 170 series. In the end you just need a good core, time, and a supply of parts.

 

I’m at this challenge with my mile 455’s. Qjets are not mysteries to me, but I’m no expert.

You’re on solid ground with the 17057553 - should be fully adjustable part throttle, center fuel inlet and optional emissions stuff in cast you want/need it. Be sure you restrain any parts purchases from places like qjet.com etc to ‘75 and later. The earlier series parts look similar, but are just different enough to throw off results.

Short run, best I can offer is O-ring the idle screws, polish the power piston bore and acceleration pump bore, plus the power piston itself (with #0000 steel wool - til shiny), then go for 73 or 74 jets with 48 - 50 primary rods (M or V, not the stepped K series). On the secondary side a good guess is L, M, N hanger and CV rods, or maybe something leaner Clean the living h*’ll out of the carb with q-tips, toothbrushes, & tiny wires to get all dirt out of the carb. With carbs, cleanliness is _really_ next to godliness.

FYI, Cliff Ruggles provides great parts. You can also get fast vacuum breaks (for quick secondary response) from quadrajetparts.com if you look. Basically it’s a stronger spring inside, but worth doing to be sure the vacuum break isn’t restraining your secondaries unnecessarily.

The qjet is an enormous search space (aka many, many, many parts combinations) the trick is to focus on what’s close to optimal for your combination. That’s hard, but doable.

Cheers
Chris

 

Cliffs book should be here sometime this week so I disassembled the carb today. I wanted to be ready measure everything to ID exactly what this carb is. It looks like during the rebuild they epoxied all of the well plugs, as well as the power piston bore. I think there is a plug in the bore with epoxy on top of it. If that’s the case I should be able to remove the plug and clean the epoxy so I can install the power piston right, or will that not be that easy? If this is going to be an issue I may just sell this carb to somebody with a big cam and build up 170 carb now.

 

OK, I've never looked inside a no-primary-rod OE carb, but anyone have any info on what they did from the factory?
Seeing something like that makes me seriously doubt the sanity of whoever was in that carb previously.

 

That is exaclty what my carb (1970 W-31) looked like after I had it rebuilt by Custom Rebuilt Carburertors. The factory used what looked like small freeze plugs to seal off the cavity but they are next to impossible to source so the epoxy is used. If you still doubt the sanity of the carb, I'll gladly buy it from you for what a powervalve style '70 carb is worth and tqake all of th erisks in using it.

For your records the 7040256 came with the following:
Main Jet # 7002658 (0.058")
No Primary Rod
Secondary Rod # 7033655 AU

 

PM sent.

 

Any suggestions on if I should try to remove the epoxy/plug and install the power piston or should I sell this one to a guy with a big cam and find a new one? I don’t want to try to remove it if it is going to damage it, but I would rather use this carb and not have to buy another one.