Hi all,

Can somebody give me is opinion on this Rochester carb on a 455, see video for a view inside the carb at idle,
is that fuel coming out normal ? And if I put my hand on top of carb to block air, 2 second and it wants to die..

Thanks

 

That carb needs a rebuild. Should not be that way.

 

Thanks 66SportCoupe, I heard of to much throttle opening could do that or too much fuel pressure (I have a new stock pump), timing is 10 BTDC, now the idle is at 800 (in park)
if I set it at 650 (in drive), the idle is not that good and if I let it idle too long it will stall.

Thanks again.

 

Are you experiencing vacuum leaks?

 

I have 17in of vaccum at idle, but I could spray some carb cleaner on the base and around the carburator.
All rubber hose are new, trans modulator is holding vaccum, new distributor advance can, new brake booster, choke pull off disconnected,
so if there's a vacuum leak it would not be that much I think.

Thanks

 

17 inches at idle is about on target. My 455’s like a whole lot more idle timing like 14°-16° degrees. Your call.

Spray some carb cleaner around the carb & see if the idle rises or falls to find any vacuum leaks in the gaskets or vacuum connections to the carb.

I’ve got a weird one for you though: disconnect & plug the brake booster line and test the carb after that.

A leaky brake booster acts like a vacuum leak, but isn’t something I looked for until just recently.

It’s not a fun discovery, but its pretty easy to rule out with a 20 minute test.

Not sure this will help, but sometimes a weird suggestion that’s easy to confirm or deny does.

Chris

 

While you’re in there, you might do the same test with the transmission vacuum modulator, if your car is an automatic.

Chris

 

The nozzle drip from your primary boosters can be caused by too much of the transfer slot exposed at idle. As cfair has suggested rule out any vacuum leaks first.
Have you done any engine modifications such as changing to a longer duration cam? If so you may need to get into the carb and open the idle circuit to compensate.

if the problem exists here are some suggestions. You need to back the idle screw off to reduce the amount of transfer slot exposed. Try introducing a vacuum leak by removing one of vacuum hoses from the manifold. if the idle goes up you will be able to adjust the idle screw down reducing the transfer slot. This could mean you need more idle bypass air.

You could also try advancing your initial timing and also hooking the distributor advance to manifold vacuum.

 

Thank you all, anyway I ordered a carb kit, and after that I'll try all of your tips and share the results with you.
The engine is stock except for the "J" heads. Does the distributor on a 71 455 use direct manifold vacuum or ported ?

Thanks again.

 

If the kit doesn't come with a float, order one.

Don't know the answer to your vacuum source question and don't want to guess.

 

Depends upon if you want a 100% factory setup or not.

From the factory there was an early emissions control device that restricted vacuum until the engine was up to operating temperature, then it allowed ported vacuum.

If you don’t use that valve, connect the vacuum advance to whichever source makes the engine run better.

 

Thanks Fun71, Sugar bear, Ontario69Hurst and Cfair,
what I forgot and forgot to say is that the actual carb# is 17080242 and I think it's from a 1980 V6 Buick or something like that,
like Ontario69Hurst said, I can try to introduce a vacuum leak by removing one of vacuum hoses to see if I need more idle bypass air,
but that carb has probably different interrnal passages so maybe that's my problem !!
If so, new carb would be the best right ?, and would you trust Rockauto, they have it ?? Or I5 interstate has it too (looks beautiful but more $$)

Thanks

 

Could look for a used correct carb by # and rebuild that or have it rebuilt. Some of the private rebuilders probably have one in stock. If you provide year, model, AT or manual, AC etc. CO members will be able to provide the correct #, everything will bolt up and attach properly. Then it will need tuning just as any carb would.

 

This is my friend's car and is ready to pay for a ready to run, so I was wondering if Rockauto would be ok or someone else.

Thanks

 

Is Rockauto ok? It depends on the rebuilder, it could be fine but I don't know. You may be able to find a ready to run at an independent rebuilder e.g., National Carb in Jacksonville FL. It will help if you can figure out the correct carb # first.

 

In my view the later 170 series (~”75 and later) quadrajets were better than the original 70 (~’66 to ~’75) series.

The later series carbs benefitted from 10+ years experience across at least a million or more vehicles which allowed GM to find the flaws in the early designs and fix ‘em. My favorite improvements are the center fuel inlet and the larger (800) cfm rating.

Plus the Adjustable Part Throttle (APT) system. APT was designed for emissions precision, but it can be used for power tuning too.

I’d go with a known rebuilder vs. buying retail, if it were me. Higher probability of bolt-on happiness. If you’re into tuning plus have time & the qjet parts, then a retail carb will be fine.

I’ve mentioned it elsewhere I get my carbs from SMI (Sean Murphy Induction) in SoCal. He’s been at it for a few decades. I’d trust Cliff Ruggles without question as well, but I have the he’s now in the parts business, not rebuilding. From what I can see from his posts & recipes, Cliff knows just about everything there is to know about quadrajets.

I buy my qjet parts at qjets.com and from Cliff at (I think) Cliff’s Performance.

Chris

 

Thanks again guy's, I ordered the one from rockauto, and will probably check rod and jets, do you think
it's too risky for the gasket to lift the top, because I dont have one in hand.
Thanks

 

I don't know what the quality of rebuilt QJets is these days, but back on around 2000 the ones I bought from the local auto parts store were really bad. Two in a row had a crack in the floor of the float bowl and would leak gas. Luckily I found that before installing, so I would say, yes, pull the air horn off and check inside. I got lucky on the third rebuild QJet, which was a Holley brand remanufactured carb. It had the correct primary jets and rods, and secondary rods and hanger for my 1971 application. And no crack in the float bowl.

 

Great I'll open it as soon as I get it, then I will share some results..
And If I poor some gas in the bowl, should I see right away if it leaks ?

Thanks

 

The ones I had leaked immediately and massively. I would leave it for a while to check for smaller leaks.

 

I'm late to the party I know. The last place I'd buy a rebuilt Q-Jet is RA. If there is anything unsatisfactory about your purchase, send it back immediately. You shouldn't have an issue unless it specifically states non-returnable. There is zero, zilch, nada, no, support at RA - none. Never expect to speak with a human - there is no support. Again, with that said, if there's anything unsatisfactory, send it back ASAP for a refund. The process is entirely automated.

 

Ok good, and no need to separate de base from the body right ?

Thanks

 

Thanks for your comment, really appreciated, don't worry I'll send it back right away if ther's something wrong.

 

Exactly what model number Quadrajet did you purchase?
Is it a Rochester Quadrajet?
What year & model vehicle is the carburetor going to be installed on?

OK. The carburetor is being install on a 1971 442 w/ the original 455? I should have read more thoroughly.

 

I ordered what was for a 71 olds with 455....
See interchange model number on pic, 90 day warranty so I give it a try !
Upon receiving, I'll check for rods and jet number, it's suppose to be in relation to the casting number.....will see.

Thanks

 

Hi again, I just receive my Rockauto carb (the rebuild is by Autoline)

Advice please the casting number is 7043250, I haven't unpacked it yet, but
there's a missing vacuum port in the front (ported) see pic. Why is it missing ? It's 1973 number but...
On the last picture, this one is from Quadrajet power web site with the same casting number but with the correct front port.!!
Is it really for a 455 ?
Thanks guys

 

I wrote to Autoline to ask them which one I would get if I return it, they told me
the last casting at Rockauto would be 7041250, but it's for a 350, do you think it's upgradable to a 455 by changing rods and jets ?

Thanks again

 

That isn't the casting number....7043250 is the Model Number. I can dig around a bit, but others may join in before I get to it, I believe that is a 1973 Quadrajet used on the Oldsmobile 350 cid engine - not the 455 cid. However, w/ that said, it most likely can be jetted to accommodate the correct jets & rods for a 455 (I think). I believe there "should" be the additional ported vacuum on the 7043250. A Quadrajet carburetor basically consists of three "tiers", from the top down: air horn (top), float bowl assembly (center section) & the throttle body assembly (bottom section). During the periods roughly equating to 1969 through 1972 (give or take maybe several years), you often will find Quadrajets which can easily be swapped between engines. Bear in mind, you can also find re-builders who use the air horn from one model number to use on a completely different model number e.g. swap the air horn of one model year onto the float bowl assembly of a different model year. That "port" which is missing may have been a float assembly used on a different model year - I am not sure. As emissions standards changed during these years, different float assemblies either did or did not maintain the same vacuum port sources. I know a fair amount, I'm not an expert - I'd have to look items up.

 

Post #6 in this thread lists the correct rods & jets for the 7043250

quadrajet stock jet size

 

I appreciated a lot your help, and sorry yes it's the model number. Ok and I could get the 7041250 in exchange (also for 350 and probably will have the missing port) but if I can upgrade it for a 455 that would be my best solution.
The spec I have to upgrade it to original is : .069 jets, 49B pri rod and AT sec rods. But no spec for the 7041250.

Thanks

 

Thanks, sorry I'm not expert so I don't understand some spec, ok for .069" jet, but .053 pri rod ? is it suppose to have a letter in there ?
There's also sec jets ?? Thanks again

 

A 1971 455 4bbl Quadrajet used part number 7041251 a 1971 4bbl for a 350 would be 7041250. I'm going to hold off on making a suggestion as to the applicability of using the 7041250 (350 cid) on your 455 even if you were to accommodate the correct jets & rods. There are better more informed & knowledgeable members who can provide you with better guidance. Be patient others will chime in.

 

Great thanks a lot, I'll be waiting for advice.

 

I'll point out a small amount of information which hopefully will assist you in deciphering recommendations by others and allow you to glean some useful information as it pertains to the usage of carburetor jets and metering rods. At some point (this might be that point in time) you would be well served to understand the nature of the sizing employed in carburetor jets & metering rods. This is a very small amount of information, but it's not a bad "basics" to get your head around which may assist you in developing an understanding on why or how the sizing of jets & metering rods will influence fuel delivery under various conditions for various engine applications - both for manual transmission, automatic transmission and the nature of how things changed during the evolution of the emissions control years.

 

Helpful if I provide the URL link, eh?

Carburetor Jets and Metering Rods

 

In the meantime, do a little research on this site and glean some useful information about the 7043250, 7041251 & 7041250 carburetors. Just type in one of the numbers and you'll launch a plethora of useful information. Some may be overwhelming, hand in there, these carburetors are relatively simple, but you need to do some homework of your own. Good Luck. Ask when you have questions.

 

Thanks again, we learn everyday !!

 

Well thanks, your are very kind sir.

 

A great source to find Delco GM carburetor build sheets is the URL link below. There are many books, pamphlets, etc. - but, I've found this site to be excellent & many are unaware of its usefulness. Click on the "GM" drop-down menu and browse by year. Have fun (sorta). You can d/l any of these .pdf files.

GM Carburetor Build Sheets

 

That missing port is the ported vacuum source for the distributor vacuum advance on my carburetor (7041250) . It is capped off and I have the line for the advance canister connected to manifold vacuum. I wouldn't send the carb back just for that missing hose nipple - check as much as you can and let the overall assessment guide your choice to send it back or not.