Hello all,

I have a 72 cutlass supreme 350, edelbrock intake, new headers with h pipe. pertronix HEI, stock cam, etc. I was wondering what you guys recommend as far as jet/metering rods for my quadrajet. I'll give you a rundown of what I have.

A while ago I rebuilt a good carb 7043250. I had the same carb on my car when I bought it but it was one of those franken carbs of the 80's that had parts from a ton of different carbs priced together. I wanted to rebuild it with current gaskets/accel pump seal that would be resistant to ethanol fuel as the old one had a leak at the accel pump. The carb rebuild went great and it runs great. Here's what I had, what I changed to and was wondering if you guys have a setup that will work for what I'm looking for.

I had 69 jets in the franken carb. I had 73's in the new one I rebuilt. I don't remember the primary rod size (sorry it was about a year ago.) I notice with the 73 jets the takeoff throttle response wasn't as crisp but on the freeway there was a big difference in power. I'm a little bit above stock but am not planning on running drag races anytime soon, (i'm definitely not jaded about the lower compression/head differences in 72) I just love the body style and want a fun, reliable street cruiser that has some cahones! I'm wondering what you guys have used as a good happy medium for quick throttle response at lower RPM and good freeway power. MPG worries went away the first time I filled the car so I'm not looking for diesel MPG. I drive it about 1-2x a week. I'm sure somewhere in between on the jets will do but what metering rods would best work with say 71 jets? Thanks in advance!

 

You pretty much need to find out what metering rods are in it and try the next smaller set available. I am assuming you are talking part throttle cruising isn't as crisp? Power piston spring selection will also affect how the rods move.

 

I figured I would need to have that info! I'll get her back Sunday and repost the metering rod #'s. I guess I wasn't too clear, It's not really part throttle cruising I notice, more dead stop to punching it response. I noticed with the 69 jets and other rods it had a little more pep off the line ( not major but noticeable) at hwy. speeds 55-65+ the 73 jets seem to react better than the previous 69's did. I did however just put headers and h pipe on, resealed intake manifold and took her for a drive yesterday and I think I Really increased the throttle response off the line! (maybe now the carb setup will match the new exhaust setup because she really took off much quicker than usual.) I'd just like to have her all dialed in. ( I did calibrate it with the vacuum gauge, advanced timing,larger plug gap,etc.) I just noticed this after I decided to try the jets/rods that came with the carb I bought to replace my existing one. All of the tips I have gotten here have been huge improvements, thanks for the response! I'll get back to you on the metering rods! Have a great week!

 

My engine seems to work fine with the factory jets and rods, even though I have a larger cam, better intake, and headers.

Primary Jets: 70
Primary Rods: 49B
Secondary Rods: AS

For a 1972 350, the factory setup was:
Primary Jets: 69
Primary Rods: 50B
Secondary Rods: CG

Properly adjusting the secondary air door spring tension is critical for a good WOT launch. You might see a big difference with as little as 1/8 turn of the adjustment screw.

 

Consider trying a primary setup of 71 jets and a 44B rod. That is very responsive in my 70 Olds 750 carb currently on a 355 SBC that has a stock type cam with headers and aluminum dual plane intake. The Olds carbs are damn lean from the factory as are the Buicks. Secondary rods are also way too lean stock. I would run something on the secondary any fatter than a .567 tip. Currently have some real rich DG .337 Cadillac rods in the 70 carb but my all purpose race Qjet has BE .410 rods For comparison on early 750 Q jets on Pontiacs that are known for there great running factory tune. The stock 68 400 engines for example run a 73 jet and a 42 rod , I actually backed down to a 72 jet with 42 rod on my 68 GTO and it was more responsive. The later large primary smog era Pontiac 800 Qjets from 77-78 still have a richer tune than the earlier Olds. Even with low compression and a restrictive exhaust the 77 350 had 71 jets and 44 rods, the 400 had 72 jets and a 45 rod and that was smog tune lean emissions carb. Bottom line is the Olds-Buick carbs were tuned for restrictive hot air single snorkel air cleaners old folks and not for high performance , I question whether they even really figured out how to tune them to optimum use. The odd big cam Olds engines 4 speed W30 and W31 had ditched the whole primary rod system with no rods and just ran little jets but yet no other division did this on their performance carbs that I am aware of. Do a search and see folks on here that tried a stock tune Pontiac carb on their Olds and how it ran. It is that simple. If you run as little as just a aftermarket air cleaner alone on a stock engine it needs a richer tune than stock then also cooler running aluminum intake high flow exhaust with headers and also 160-180 T stats require richer tune. Here is a handy secondary chart for rods to see where you line up on the list and being at the bottom is not a good thing. http://www.hioutput.com/tech/qjetrod.html

Also there are still a nice range of new jets and rods available for the 74 older style Qjet

http://www.jegs.com/p/Edelbrock/Edel...49166/10002/-1

 

As always you guys are the best! Looks like i'll have to play with it a little bit on my days off and see what works best! Thanks again for all the great advice!