I just had a guy replace my clutch for me and he was commenting on the overall car, saying it was very sound, very nice but he didn't like the Rochester that was on it. The engine in the car is a 350 with the CKD suffix and the carb is an emmision (piece of crap as he called it) Rochester. The left bank is running richer, you can see it on the plugs and in the exaust so somethings up. He suggested not messing around with my carb and that he has a Rochester off a 71 he wants to put on it. I am not a carb expert in the least bit, what's everyone's thoughts; Rebuild (or tune) the current carb or take him up on his offer? Besides adjustability what really are the differences? My carb works great except for the left side issue.

 

What is the part number of the Q-Jet on the Vette now? If it is from the late '60's, it should only need a rebuild. If it is from the late '70's, then the '71 carb. may potentially offer better driveability. Can you provide p/n's for both carbs?

 

I will get that info tonight when I get home. My mechanic said that it was a late model smog carb (the one on there now), that's all I can say for right now.

 

Probably you just have a leaking fuel well plug, its not an uncommon problem on the QJets. The fix is renove the carb and coat the plugs with epoxy. Will cost you $5 for the epoxy compared to the cost of replacing the carb.

If you want some good info about QJets including other possible causes for your problem and fixes click on intake and tuning of this link and read anything written by Lars. You will also find info on how to adjust your carb to get more performance. When adjusted properly QJets offer the best compromise between emissions, driveablilty, fuel economy, performance and reliability (as far as carbs go that is, obviously fuel injection is better).

http://wiki.corvettefaq.com/index.php?title=Engine

 

I’m a little confused by your diagnosis. Are you saying that the left side plugs and exhaust are odd, because if you have a duel level intake manifold then the left bank of the carb feeds the #1,4,6, and 7 cylinders, or is it the 2,3,5,8 cylinders? Either way having one side of cylinders run differently may not be the carb alone.

 

If your carb is a 4ME, then he may SORT OF be right. The late and early model q-jets are not much different. There's only a few things they changed on them. You can make a 4ME run just as well or better than a 4MV (early model). The advantage of having the 4MV is, strangely enough, parts are easier to get for it. Getting the correct primary metering rods for the 4ME is a pain, lars had to "make" mine (adjust the M rods power tips which are the only ones available.)

 

OK, I'm about ready to give up
I can't find anything that says 4ME or 4MV anywhere on the carb, where do I look?????

 

4MV is the carb model designator - it's not on the carb. You're looking for the carb number. It's stamped into the float bowl, vertically, on the driver's side above the secondary throttle shaft. Post this number. It starts with either 170XXXXX or 70XXXXX depending on year.

The carb will not make one side of the engine run richer than the other due to your dual plane intake manifold.

The later carbs run just as well as the early carbs. There is no difference in performance if the carb is correctly set up. Some of the most brutal performing carbs I test on my car are 77-79 Q-Jets.

 

Hello,
Here is some information on Rochester Quadrajet carb identification.

website is: http://www.oldengine.org/unfaq/leadfoot/qjet1.htm

You can usually find the carbs casting number and date code on the driverside of the carb stamped vertically.

A typical stamping;
7045213 YA
101 5

70 = Rochester products division#
45 = Production year, 4=1970's, 5=specific year, 1975
2 = Carb ID, 2=49 state Q-jet
1 = Division, 1=Chevrolet products
3 = Tranny ID*, Even number=Automatic, Odd number=manual
101 5 = Julian Date Code, Friday April 11 1975
YA = Engine assembly plant

# Carbs starting with 70xxxxx are pre-1976. Carbs starting with 170xxxxx are 1976 onwards.
An important note: Primary metering rods are different lengths for the two units, both rods are available from GM, and the new-part part numbers correspond with the carb. Rods whose p/n starts with a 7xyz are for the 70xxxxx carbs, and p/n 17xyz are for the 170xxxxx carbs.

* tranny ID is not cast in stone. This particular example was original equipment on an automatic equipped pickup truck.


Production Year
15 = 1960
19 = 1961
20 = 1962
2x = 1963-1969
3x = 1966-1967 A.I.R. equipped vehicles
4x = 1970-1975
5x = 1976-1979
8x = 1980-?

x=last digit of model year

Carb ID
0 = 49 state mono-jet
1 = 49 state 2bbl
2 = 49 state Q-jet
3 = California mono-jet
4 = California 2bbl
5 = California and high altitude Q-jet


Product Division
0,1,2 = Chevrolet
3 = Cadilllac
4 = Buick
5 = Oldsmobile
6,7 = Pontiac
8 = Non-GM, possibly Mercruiser Marine
9 = Special


Julian Date Code
From our above example code;
101 = Day of the year (1 thru 364/5)
5 = Last digit of manufacturing year. (0 thru 9). Utilize carb id for 60's, 70's, or 80's.
Some of those multiyear calanders with a look-up table have the Julian day of the year on them. If not, you'll just need to count out the days.

 

The rods for the 1975+ carbs are no longer available from any source. Only truck rods with the fat (lean) power tips are available for the late carbs, and these are not suitable for Vette applications.

 

I guess I thought the edelbrock carbs might have the late rods?

 

Can you explain this a little better for me? any pics of this process? or a link to the supplier of the epoxy? I am in the process of putting mine back together and am trying to learn everyhting i can while doing so.

 

Here's some links that show you :

http://www.4wheelnoffroad.com/qjet.html



http://www.florida4x4.com/tech/quadrajet/index.php



http://www.corvettefaq.com/c3/QJetTuningPaper.doc

Also, http://www.carburetion.com/ has some information and parts kits!

 

Good post. I was always curious about carb designation vs casting number. i bought a carb at a swap meet "off an 81." No M/C solenoid so I knew he was wrong, but didn't know the vintage. I bought it to learn rebuilding before tackling my E4ME (which works very well but has a leaking upper gasket).

 

The 1975+ style EDL carbs have late model rods. They're the truck rods. You can buy late model truck rods all day. Late model passenger car rods are not available.

 

Good links...the top two were new to me. I noticed that one web site said JB Weld is OK to use as an epoxy and another said NOT to use it.

 

The carb # is 17081250. I spoke with my mechanic and he said his did indeed come off his 71 and will let it go with manifold for $100.00. Was working fine when he took it off. I don't need the manifold but what the heck. Good deal for $100 bucks??

 

Great deal! Plus, it has the correct style choke for you Vette.

 

It's a 1981 Q-jet and according to Lars not performance oriented........
Gonna jump on the 71. Any suggestions before I bolt it on? Also, what kind of a choke should it have??

Thank you for all the replies fella's