Hey all,

I am tuning my 383 with a non cc qjet from 1979 (or so the book says) that has some 50B primary rods. I have calculated from the amount I have the APT screw backed out and my A/F meter that I really should be running something more like a 46. Question is, can I just order the edlebrock replacment or is there a difference between rods (length and such) so that I can only use rods stamped with a B.

I have heard that there are differences between different years of primary rods in qjets and dont want to spend 10 bucks without at least asking the question on here!

Thanks for the help.

 

I think pre 1975 was the shorter rods, so those aren't interchangeable. I think Edelbrock sells them as 1974 and before, and 1975 and on. So you can buy any rods for 1975 and beyond and they should work just fine. Or go JY diving for 46K rods (good luck, let me know if you find those 'ghost rods'.)

 

AHH ok I see on their website
http://www.edelbrock.com/automotive_...ss_q-jet.shtml

Primary Metering Rods (pairs)
Single Taper for Q-Jet Model M4M (1975 & Later). Dimension indicates maximum diameter of taper.
(.048") #1941
(.050") #1943
(.052") #1945
(.054") #1947


I guess I can only get a .048 then?????

Oh well I guess itll have to do. I would have thought with my 76 jets I should be pretty rich but not so. And the WOT F/A with the secondaries locked out is perfect at 12.5. So all I really want is a thinner rod during cruise. Maybe my calcs are wrong and a 48 will richen me up alot more than I am thinking...

Oh wait -- here it looks like Jet Chips is selling rods
http://www.jetchip.com/products.asp?pid=27486

They list 50-52 "M" rods, 39-44 "B" and 40-44 "K"

Which ones should I be looking at M, B or K?

Thanks again...

 

See what I mean? 46 is a ghost size. It doesn't exist. It's a little black hole.

I know K rods fit in post 1975 Q-jets. M ones have a .036" power tip IIRC, whereas others use the .026" power tip. Not sure about B ones.


Measure the power tip of your current rods. If you're going to a rod with a different power tip, make sure you change the jet size as well.
I'd get some 44K rods, and some 48 rods and find out which works best.

Sounds like you're doing some serious tuning with your q-jet, i'm impressed. I finally got a wideband setup, so i'll be doing the same this spring.

 

well serious is because the wideband stares at me in the face with a 15 when Im on the highway. and thats average of driverside bank. I can only imagine what the rear cylinders are actually running (15.5 or more !!!)

I think Ill take your advice and start with the 48s -- you know what they say, baby steps....

 

Running down the highway with my TPI, I am running 16.0:1 on my wideband.

 

Non-cc QJets had 2 different length rods. The earlier QJets with a divorced choke (choke bimetal spring mounted down on the intake's exhaust crossover) used the longer (B) rods. Everything with a round choke housing on the passenger side of the carb used shorter (K) rods. M rods are the same length as the K rods but with a fatter (leaner) power tip.

Put your current rods in your micrometer and check the power tip diameter. If it's .026" then they're K rods. If it's .036" then theyr'e M rods.

I think your calculations on what rod you would need to equal your current setup (taking into account the APT adjustment) are probably about right, maybe just a smidge rich. I agree that something in the range of .046-.048" is absolutely within the range of sanity. I run a 76 jet/46K rod as my go-to starting point when I'm first setting up a QJet and need a baseline calibration. You're on the right path.

Primary rods can be had in those sizes from several sources, although they are getting more scarce.

I'm not a fan of the Edelbrock rods becuase they SAY they are "K" rods but when I have actually mic'ed them they have .035" tips, which means they are M rods in reality. I've also found they have different diameters than what the packaging says sometimes.

 

Excellent Info Damon! Thanks. Any suggestions where to get the 46K rods?

355 - That is pretty high but even TPI has better fuel air distribution than most cross H carb manifolds. I have heard that cross H's can have as much as 3 points of variance in F/A ratio between cylinders. Average might be 14.7 to 1 but one of the cylinders could be 17!

TPI is better with the variance usually limited to a point or less.

 

If this wasn't pulling around a 6K lbs fullsize van, I would go even leaner without hesitation.

 

The Carb Shop in Ontario, California (not Canada).

 

Yeah -- Carb Shop says they dont have ANY primary rods anymore.

I guess Ill just order the .048 edlebrocks then.

 

Maybe try this place in Stony Plain;

http://www.carburetor.ca/carbs/HTML/about.htm