BigBlockk

The primary rods control the cruise mixture. Idle fuel is taken from the main fuel well so the total amount of fuel for the idle, off idle and cruise systems is increased if you go to a smalled rod. It is also possible to get a little better fuel mileage from the smog cars by richening up the off idle circuit.

BigBlockk

Later.....

lars

Yes, if you go to a smaller rod, you will richen up the idle circuit, transition circuit, and the cruise circuit. Your 77/52 combo is a little lean - good for mileage and low CO. The 77/48 would be a good combo for a performance application on a car with headers, good intake, and/or an aftermarket cam. 77/40 will get you way too rich - no reason to even try that one.

Keep in mind that if your carb is a 1975 or newer Q-Jet, primary rods are not available unless you've scrounged some out of a used carb...

TopGunn

Having a 75 carb and having worked on it over the past two years I would recommend you ditch it and get one from a different year if the suggestions Lars makes don't show any results, 76 thru 78 make good choices. 75 was the first year for emission standards, the idle circuit in them is terrible. And you can take that to the bank!

Bob Onit

Lars.... I know they are not avail from GM any longer but has Edelbrock stopped selling them as well?
Do you know if Edelbrock manufactured their rods or if they got them from the same source as GM?

Tim H

Now that is good info!
I just changed out the #52s with the #48s, cut 1 coil off the power piston spring, put the float at .420, adjusted the carb and I think its loping a little more with the extra fuel and lost the hestation.
Im going to drive it after the rain clears out later and will get back with results!

lars

The Edelbrock rods are truck rods with .036" power tips. These cannot be used in a Vette carb without completely messing up the WOT metering area/mixture. Passenger car rods (Vette application) with .026" power tips are not available from any source.

Tim H

With my changes, I actually can feel the difference.
It feels like it should where a person could say they have no problems.
I would rate this little experiment as a success.
Next is an electric choke before winter.
(PS) Im glad it was explained that the primary rods are what richens the low end and not only the jets.
When its explained with percentages I myself get confused as maybe others do then get discoraged in going any further, but want just parts that go togather for results.
I used "CV" secondary rods because they were just like the "BG" and its the smallest tips I had right now.
The carb sounds like a jet plane when I kick it in!

lars

Good job!
Lars

BigBlockk

I thought you were one of those that didn't like the "Quadrajunk".

BigBlockk

Later.....

Tim H

I also push to the limit of no doughts sometimes.
I also learned to push the pin holding the pump arm out then lift the top strait up instead of turning upside down trying to snake the linkage out of the arm hole!
The pump is still a little bitch though!!!!!!!!!!

lars

Hey BigBlockk -
I think Tim H is saying that he's trainable...! Looks like we're going to be able to learn him a few things about Q-Jets yet!

Black'69

I made the mistake of trying a Jet Performance rebuild from Summit. Lets just say that now it's in the mail being returned to sender.

Then I did the smart thing and sent the old Q-jet to Lars for a retune. The thing now runs like a top.. bad @ss!

The Jet rebuilt had a miss off idle, hestated under load, at times it would bog and you could just smell the raw gas coming out of the pipes. Lucky for me I convinced Summit to take it back and refund my money.

You can tell by the writup Lars did that he understands the Q-jet inside and out. What a great resource to have on the forum... Thanks Dude!
~C

BigBlockk

Well, maybe we have another convert.

Ya know Lars that could be good and then again that could be bad. When we finally got Bob Onit to stop cussing at his 'Jet he started buying up all the cheap cores. The boy done went crazy on us!

BigBlockk

Later.....

Bob Onit

No, they're such garbage that I bought up all the old parts and cores I could get my hands on so nobody would ever have to live through the Q-Jet hell that so many of us have.
I used to need all this to keep a single Quadra Junk running for about a week.



Then I spent $350 on this, and all my problems were magically solved forever!

lars

Hey Bob - Can I have your power pistons since you don't need them anymore...?

Bob Onit

If your serious I could send you some.
I have more than are in that picture.

Patrick73

Lars, Would the discontinued 750 CFM Edelbrock Q Jet model 1901 (for 66-73 chev) be acceptable to run on a stock 73 L82, 4 speed, with its .069 main jets, 36B primary metering rods and DR secondary--or would you recommend rejetting before using the carb on a non modified 73 L-82?

Thanks!

Tecdiverfl

My carb is at Lars now. The guy I bought the car from bought the carb from Chicago Corvettes. I think the receipt said he paid about $600 for the carb with anodizing. The carb was put together with many of the issues mentioned above. The only saving grace for me was the car was running so poorly that I could not get on it hard. So when I spun a bearing I did not blow the entire thing up. If I had a decent carb on the motor I would have hate to seen the damage when I lost oil pressure to the front of the motor.

lars

That's not a bad carb. It is a duplicate of a Chevy truck carb, and as such is jetted very lean. You can try it out in the stock configuration, then switch over to a 74/44 jet/rod combo and see if it wakes it up a bit.

markdtn

That is an interesting statement. I'm sure you are right, but I have found most 100k mile+ q-jets that I have seen have loose throttle shafts. You find that most do not? I thank you for your efforts to keep Q-jets going. It is a great carb when set up correctly.