Chris289

Hi guys, just need a quick piece of advice. The 68 Cutlass I've been building is just about ready to go back to it's owner. I've a problem with the carb overfueling, it's literally pouring fuel down the chokes on idle and adjusting the mixture doesn't do anything to help it. We have have stripped the carb down to inspect the float and found it's full of dirt and crap and looks old and worn, I can't even get the float out of the carb as parts of the carb are siezed solid. It's not worth rebuilding this one as it's going to need various parts replacing to make it work again. The carb is a rochester quadrajet with electric choke from a 78 Cadillac, part number 17058530. I can get a Holley or edelbrock carb in the UK but need some advise on which one to get. Size and part number will be great. Again, the engine is a stock 455 from a 75 car originally with stock manifold. Any help would be much much appreciated.

Many thanks

Octania

A nice new or requilt QJet is readily available here
They run as much as $500 for a new one, never been used. Those are typically Hot Air / Electric choke and numbered like a 1967 carb, but will work on many such engines of course with some jetting changes as needed for your exact engine. The rebuilt carbs are somewhat less expensive but I hear they may have pressed in inlet seats for repair. I have sold quite a few used ones with no complaints yet though.

Chris289

Rochesters are not ready available in the UK though were as a Holley and edelbrock are. The car is not concourse so doesn't need a date numbered carb. Just need one that's fits the engine and suits the engine. Appart from this the car is done and ready to go back to the customer.

joe_padavano

Please take this a a constructive comment. Adjusting the idle mixture screws certainly won't have any impact on a flooding problem. That's not how the idle circuit in a carburetor even works.

The idle circuit doesn't flow fuel through the venturies. Idle circuit fuel sprays into the carb through the idle ports below the throttle blades. Fuel pouring down the venturies is the result of a stuck, sinking, or improperly set float.

As Chris noted, the best carb for this application is a properly rebuilt, correct Qjet. Unless the carb casting is badly corroded or cracked, it can be rebuilt. I'm struggling to visualize a scenario where the float is so "seized" in a Qjet that it can't come out. Once you have the air horn off, the float is only retained by a piece of steel wire that serves as the pivot. This wire slides into the float bowl casting in slots. If the actual needle is stuck in the inlet fitting, both of those are replaced in a normal rebuild (and this would be one possible source of the flooding). The float should also be replaced if it's plastic, as today's gasoline additives will attack older floats.

Of course, you've also got a mismatched carb on a smog motor. You'd be much better off with a late 1960s-early 1970s Oldsmobile Qjet. The electric choke coil will swap onto the hot air choke housing. Duplicate the factory jets and rods for a 455 motor. The owner will be much happier with that combination.

Chris289

Yes, I know how the idle mixture screws work, I typed this out wrong, I meant adjusting the idle mixture screws isn't helping how the car runs. It's flooding itself with too much fuel, I was trying to state that it's not the mixture causing the problem and elsewhere.

I stripped the carb with a few other mechanics, both Classic American car guys, they both said the same thing I was thinking, the carb isn't worth the cost and time to rebuild and will be quicker to replace it, the body is badly corroded inside, it can be saved but would need going in hot tank with chemicals to clean it up plus it looks worn, there is a small part that is ment to slide up and down freely above the float that you need to remove to get the float assembly out, I don't know the name of it but it has 2 small needles hanging from it, one either side, this was stuck solid, after the decision to replace the carb was made we decided to continue trying to strip it, after alot of struggling got the carb stripped completely, the body is corroded like at some point in time the carb was sat out in the rain, things don't move freely on it, it just a lot of work to rebuild it more than the average carb would. In my opinion it would be quicker and cheaper and make a better job of the build to replace the carb with a new unit, now weather that unit be a rochester, Holley or edelbrock, I don't know and that's the advise I'm after.

Also like you said, this is the wrong carb for this application anyway.

Were is the best place in the USA to get a correct q-jet? Summit only list rebuilt ones and don't show them in stock, we need this ASAP which is why if a Holley would work and perform the same as a q-jet then for us this will work, but if a company can overnight one to the UK then we can go down the q-jet route is that makes sense.

Chris289

I should also mention we believe this engine may have been in marine use at some point, it originally had a marine use water pump on it and the fitting in the rear of the inlet was replaced with a blank and the engine was rusty, if the engine was in marine use at some point in it's life before being put in this car then that would explain why the carb is so corroded inside having spent time sucking in the sea air with all the salt in it, was just a theory.

Would this carb be any good? It's listed for a 75 455:

http://www.summitracing.com/int/part...ake/oldsmobile

joe_padavano

The stuck part you're describing is the power piston, and those needles are the primary metering rods. Today's ethanol-laced gasoline can easily cause corrosion, especially since the ethanol absorbs water.

In any case, I'm not a fan of Holley carbs for street use. They are great W.O.T. carbs for the track, but lack finesse at mid-range metering. Also keep in mind that any Holley square-bore carb will require one of the flow-restricting square-to-spread bore adapters. Don't believe anything that Chevy-centric parts vendors like Summit say about parts fitting Oldsmobiles.

You really want an Olds-specific Qjet, not a generic one from a mass rebuilder like Jet. You won't get one of those overnight. A second choice would be the Edelbrock, about 750 CFM or so. It's a square-bore carb but has both bolt patterns so it should fit on the stock intake without an adapter. You might need a spacer for throttle arm clearance, depending on the manifold and EGR configuration. The E-brock has a more sophisticated midrange metering system, using rods like the Qjet. It also has a air valve on the secondaries, like the Qjet, though it does lack the triple primary venturies that really give the Qjet it's flexibility. In any case, I think that will be a better choice for a street driven car.

Of course, ask five people to recommend the "best" carb and you'll get seven answers.

Chris289

Lol yes I know exactly what you mean. The 2 guys helping me today both like holleys, I like edelbrocks, used them on several mustangs with happy customers.

Do you have a part number of an edelbrock that would fit the stock 455 iron intake? Summit don't list one that fits but if they sell one that fits then I can overnight it or my UK supplier may have that one in stock. Just need to know which one it is.

Yes, power piston, that's the part, it was siezed around 2/3 of the way up of it's travel, weather this was the main cause of the problem I don't know but it certainly can't be good for the carb either way.

Thanks for the help

cutlassefi

If you can't get the correct Qjet or get that one to work then get a Holley 770 Street Avenger or Quick Fuel 750 Slayer. They offer electric choke and should run pretty well right out of the box for your application. And the Slayer actually has a better cruise circuit than a Qjet or Edelbrock carb.

Summit also sells a series of plates and gaskets that you can change around. Those plates will cover the spread bore part of the carb mounting flange. I believe Edelbrock also sells and adaptor that's far less restrictive than what Joe mentioned. Check it out, let me know if you need anymore info and good luck!

Chris289

Thanks guys for all the help, shall call my UK suppliers on Tuesday and see if they stock the parts I need. If not then guess I'm stuck waiting for parts from the USA.

Thanks again for the help and advise

oldcutlass

I'm not a fan of the adaptors, if I were to change to a square bore, I would also change the manifold. A well tuned Rochester on stock manifold is hard to beat. While Holleys have their minor quirks, I like them better than Edelbrocks.

Backstrom

I would say q jet 7 days a week, but for a couple of years ago (maybe 20...) i had a '65 skylark with a bone stock '75-76 low comp 455 olds. Ran terrible and needed a new carb. I bought a #1406 edelbrock 600, economy calibrated w electric choke.
Ran like a champ right out of the box. I think a 600 is a very small carb for a 455, but maybe that's what made it run so smooth.
It did have some power too, 20 meters of rubber from a stand still with 3.08 posi and 255/60's. My father in law still talks about the neighbors complaining. Lately I've had an edelbrock 750 on a higher comp 455, but couldn't get it right in any way. Had to take it off and got a good qjet instead. Much better.
/Anders

Chris289

Well we went with a Holley 770 ultra street avenger and adaptor on the end. Had to modify the throttle cable bracket (bit of cutting, welding) and a few other adjustments and mods to hoses but the difference out of the box was incredible. The car was running nice before whilst it was cold but no where near this well. We fine tuned it tonight and got it running even smoother. All I can say is there is a reason Olds called these engines a rocket engine, it damn well goes like one! Very very happy with the result and I'm sure the customer will be too. Just got to give the car a good clean up then it's off back to it's owner.

Many thanks for the help and anyone else that needs a new carb, I'd quite happily recommend this one.

Chris.

cutlassefi

I figured that would work well for you. Glad it's fixed.

ELY442

My Holley 750 cfm vacuum sec, for some reason ran super crazy rich and the car ran like crap. A friend of mine loan me his Holley Aluminum Street Avenger 870 cfm, vacuum sec and WOW, my car became a beast. I dont think I want to give it back to him.

Chris289

Yep, this ultra street avenger is awesome!