Hello ~ Well now that my interior restoration is mostly complete - I want to start on some performance and maintenance repairs. I really think that I must start with my Carburetor as she idles rough at times and when cold - it's much worse. Engine is strong and fairly tuned so i think the fuel system is a great place for me to start. I believe that she is all currently Stock. This area is very new for me so I will look to all of you experts who have been through this to guide me. Should I rebuild my existing Stock Carb or Replace it? If rebuild - any advice? If Replacement - any advice? Also - while doing this work - are there any related tasks that I should strongly consider at the same time? Thanks a lot and I can't wait to start seeing some replies on this... This will be fun.

1978 Stock L48 with Automatic Transmission

Cheers ~ Joe

 

tell us about the carb adjustments that you have done so far.

 

Oh i have done absolutely nothing so far with the Carburetor... I do know that it has not been touched in a couple of years (when i purchased the car). It was on the list of things to be repaired/rebuilt - that the Mechanic who inspected the car for me (before i purchased it) created for me. I do know it should be done... Just not sure which would be easier/best... to rebuild or to replace. And if i replace - should i just stay with a stock Carburetor? This is not a performance car - she is just a cruiser

Thanks in advance!

Cheers ~ Joe

 

The original Quadrajet is a superior carb to any aftermarket replacement. If it needs it, rebuild. Buy a kit, a gallon of lacquer thinner, a non-plastic bucket and brush. Disassemble recording all adjustment settings. Soak and clean, forcing cleaner through all passages. Reassemble with new parts from kit. 95% of the time that will do it.

That said, are you sure the problem is the carb and not ignition? Always check for ignition problems first.

God bless, Sensei

 

Thank you Sensei,

This is the sort of thing I was hoping to hear. I have had the air cleaner off and the Carb does look a little dirty and gummy... I know that even if it isn't the direct cause of my rough running - it certainly must be contributing. I'd like to do it for a couple of reasons. First of all - i just want to make my little 78 Perfect, and Secondly - I would like the experience and satisfaction of doing it myself. I will do exactly as you suggest. I'll buy the Rebuild Kit, and the cleaning materials you suggested. I was considering purchasing the Carb Manual as well... do you think that a wise investtment? Keep in mind - that i have never worked on a Carburetor in my Life. But i'm very mechanically Inclined

Are there any other Springs, Parts, Cables, Fuel Lines, etc... that I should consider just replacing at the same time?

Regarding the ignition - any suggestions there would be humbly taken too

Thanks again.

Cheers ~ Joe

 

You might look for a Local Carb shop and have them go threw it. I carb of that era probably has plugs where the idle air screws are and such and a carb shop will know how to make it run better then it did when new.

 

For a C3 Corvette, rough idle is usually due to one of three problem areas (or a combination of them): carburetor, ignition, and the vacuum system. Rebuilding the carb is a good idea whether it resolves the immediate problem or not. If you have an induction coil [pickup] type timing light, just check out each plug wire for proper firing when the engine is idling...if the ignition is 'missing' you will see omitted pulses in the light & that will even tell you which plug/wire(s) are the problem. Vacuum leaks are a common cause for rough idling; even a little extra air into the intake mixture can cause erratic idle quality. To test if the vacuum system is involved, seal off all direct lines to the intake manifold: remove and cap-off the main vacuum system line from the fitting on the intake manifold; remove the vacuum line from the power brake booster (if you have one) and plug it off before you start the car for your idle check; the late 70's automatic C3's used a 350 tranny with a throttle valve cable rather than a vacuum modulator...but if you have the vacuum mod type tranny in your car [for whatever reason], you need to remove the feed line and cap-off that fitting also. Once all of the vacuum source lines (potential sources of vacuum leakage) are sealed of, you can do the idle check and see if the engine runs better. If it runs fine, you then have to connect those systems back...one at a time...until your problem returns. That will indicate the individual system which has the leak; you will have to diagnose further from there until you find the leak and repair it.

I hope you find your problem quickly and that it is not a difficult fix.

 

As stated above rebuilding is a good idea for a couple reasons;
1, you know what you have. If you get a "Rebuilt" unit, you will not KNOW what you have, it could be full of errors, dammaged or mismatched parts and bubba fixes.
2, you get to learn something
3, as stated by A1Sensei, the Rochester quad is a Very good carb and very hard to beat. If you don't feel comfortable doing it yourself( it does require some skills) then find a competent guy to do it for oyu, check local vette clubs, car clubs etc.
4, It gives you a baseline Known Good point to start from

 

+1 for a rebuild by a Q-Jet specialty shop (not the local shop)

 

Guys - Thanks so much for all the great input. It's just great to share these experiences with all of you and to get your thoughts and Ideas.

I will rebuild the carburetor. I think i'll go ahead and get the Carb Manual as well - it will help to guide me... There is one out there specifically for this Carburetor.

Perhaps it got lost earlier in the thread - but are there any other Parts I should consider replacing at the same time? Springs, Fuel Lines, etc.... While i have it apart - i may as well replace the easy to get-to parts... I am definitely going to perform the Vacuum Tests recommended as well as the ignition Tests. I think those are wonderful ideas.

Thanks again and I'll certainly keep you posted on the progress... I may even throw in a photo or two

Cheers ~ Joe

 

This should go without saying but absolutely do not put the rebuilt carb back on with out a new fuel filter. A quadrajet's filter is at the fuel line inlet to the carb.

 

The above is good advice, and in greater depth than I would have been able to provide

But reading it, one other thing came to mind, in that you said the idle was rough when the engine was cold. This would lead me to check the choke for proper operation.

 

The Filter was already in my online Shopping Cart

I am beginning to fear this rebuild now however.... After doing a bit of research on Rebuilding this Rochester Quadrajet - I am getting the message that it is quite a complicated process to rebuild one of these; with many areas of potential frustration.

Should I just send it off to a Carburetor Specialist to have it professionally rebuilt? Or is it something that I can handle with Patience, a Good Guide, and My own mechanical aptitude? I Certainly don't want to make it worse... On the Contrary - I want her to run perfectly when done.

If i do decide to send it out to get it rebuilt - any recommendations on a trustworthy shop? I don't mind shipping it out - but i live in Katy Texas so something local would be preferable. Ive searched online but cannot find anything local.

Thanks again

Cheers ~ Joe

 

 

Don't be afraid to rebuild it, just be careful and take your time and you can't ruin anything. (Don't take the butterflies off the throttle shafts)

As I said before, record all adjustments as you dis-assemble: Screw adjustment screws all the way in, counting turns until seated, write this number down and re-set when putting it back together.

Get everything really clean, especially passages. force thinner through with a bulb (wear goggles) and/ or blow compressed air through.

You might want to replace the float while you have it open and definitely the fuel filter (air filter if needed). Other than that, a standard kit should do it.

If you have problems down the road, we can usually talk you through it. If you are still thinking of NOT doing it yourself, PM me.

God bless, Sensei

 

Joe,
Are you mechanically inclined? What other 'hardware' have you disassembled and successfully reassembled? If you don't have a set of basic hand tools and don't know a Philips screwdriver from an Allen screw, it would be best to have someone else rebuild it...or, at least, be with you to guide you. Having it rebuilt is less expensive than buying something 'off the shelf'; but the real savings happen when you can DIY. Do what is best for you. {But I still wouldn't put anything on that car but the Q-Jet you already have.}

 

I am about to do the samething and also live in the Houston area.

I found O-Reilly's stocks the kit and fuel filter for $20 if you don't want to order one.

 

You can re-build the Q-jet yourself, it's not really that bad. There are some really good write-ups on this site from Lars about tuning these carbs so you might wish to read up a bit on it.

That being said....I usually run into 2 different types of Q-jet rebuilds. The first type is a simple 'clean it out and replace the serviceable parts'. The second type involves pulling the throttle shafts, drilling and pressing in shaft bushings and while you are at it....re-plugging the metering jet wells. The second type is a bit more involved.

Before you decide to tackle the carb yourself...you may want to try and qualify your carb status first. A good check is to spray a bit of carb cleaner at the place where the throttle shafts exit the base plate (while the engine is running). If the engine idle increases, then you will need to drill for shaft bushings as part of your rebuild. With leaking shafts, it will be almost impossible to tune your carb correctly.

Does your car start right up after sitting for a few days or do you have to crank it for a bit first? If your metering wells are leaking, then the float bowl may drain of fuel when the car sits for a few days. The driver then has to crank for a bit (pumping the carb full of fuel) before the engine starts. If you have this symptom as well, then you will have to fix the plugs when you get the carb apart.

If your car doesn't exhibit any of these last two symptoms, then go ahead and rebuild it yourself. You will be happier knowing that you did the job yourself and learn a bit in the process.

 

Ok Ok darnit - you guys have talked me into rebuilding it myself. What the heck... if i mess it up i can always send it off to be done right

I will be extremely methodical and Take lots of pictures, record current settings, etc... I do know my way around a wrench pretty well - i just haven't tackled a Carburetor before. You guys are giving me great confidence now so i have to try... Although i may be cursing you in a few days hehe.

I will definitely check the local parts store now ... i didn't think it would be such a common kit to find. I will also perform the bushing test suggested by you Bronzie I don't know their current state. Regarding the Metering Wells - i do have to crank it a bit more after sitting for a few days... so i may have that problem. is it difficult to fix?

I will give this a go - and Keep you posted. It sure is nice to know that I have some experts helping me on this end if i get myself into trouble. Thanks a bunch and Look for updates soon

Cheers ~ joe

 

Buy a new Nitrofil float and a good quality kit. I don't know about the "cheap" kits; usually the instruction sheet is illegible. If the store you go to has this type of float (solid, black plastic foam float) and the kit has good instructions [ask them to open it and let you look before you buy it], have at it. NAPA used to sell decent kits, but that could have changed in the last few years. Maybe others can recommend a good source to buy from.

Get a good book on the Q-Jet with sections on 'how it works', 'how to rebuild it', 'how to fine tune it', and a section on specifications for various units. Read it first...until you feel you understand what needs to be done; you can always refer to it, if you are uncertain about something. Just take your time and do it right the first time! That will save you time from having to re-do it to get it right. Taking a Q-Jet apart is probably easier than taking a toaster apart....it least, the carb was designed to be rebuilt. You can do it.

P.S. The first sentence in your last post is my mantra for all mechanical work...."If you are going to pitch it and buy a new one anyway, you might as well take it apart to see what's wrong. If you can't fix it, you've learned something new; if you can fix it, you've saved a bunch of money." Trying to fix a 'kaput' part is always a win-win situation.