Well the easiest to do is go with a larger rod on the primaries. If you really want to get in to tuning your Q-jet, I highly recommend getting a copy of Rochester Quadrajets published by HP Books. Well worth it has it has lots of tuning tips along with rebuild instructions.

 

Hi 73shark, thanks again for the help and suggestions.
I got a gallon can of Gunk Carburetor cleaner today, it only holds 3 quarts but it comes with a bucket to submerge the small parts in.

Took your advise and NOT soaking the power piston, accelerator pump or the choke pull off. I got to page 6 of the link-"Disassembly". So far so good. The top part of the carb is soaking in a pie pan and the small parts are in the basket. Tomorrow I'll soak the middle part, the float bowl, and I'll put the throttle body in after that.

I'm not sure what you mean about putting something soft behind the accel pump, can you clearify that?

Heard that Echlin Rebuild Kits are best so I'll try that.
Also heard that Nitro Floats are best so I'll get one of them,
and a new fuel filter too.

Larger Rods let in less fuel, that's what I needed to know, I do have both the HP book on Rochester Carburetors and Cliff Ruggles book but they seemed to complicated for me and it seemed that there emphasis was on performance, I have a stock low HP and low compression motor so I'm trying to get better mileage. I'll contact them to see if they have the larger jets.

Thanks again for all the help, PG.

 

Hi pg, I wonder if your carb has been tinkered with before, the size 75 primary jets seem a little large for the application but if you already have some larger primary rods or have ordered them then it sure wont hurt to give them a try first. Most of the Q-Jets that I've torn apart from the 1970's used jets around size 72. The important thing when making changes is to only change one thing at a time and then test it, if you change jets and rods at the same time your going to be guessing at the outcome. Congrats on tackling the Q-Jet rebuild, most folks are deathly afraid of them, I love 'em, lots of tune-ability, good performance, good drive-ability.

 

Hi 78buckshot, thanks for the input and encouragement. I have my test carb apart and so far I've cleaned the top, on my 4MV exploded view they call it a "Bowl Cover Assembly", cleaned the "Float Bowl Assembly" and the "Throttle Body Assembly" is still soaking.
This Q-Jet has a number 7028212 stamped on it, and your right someone has messed with it before. The main jets are 71 which it what it was made with, but the main rods are listed as 46 but someone put in two 37's.
I have to work the next 3 days so I won't make too much progress on this project, but if I can get the test carb back together, which I think I can, than I'll try the rebuilding the carb on my DD and I'll do like you said, I'll try one rod larger and see if I get any better mileage, than I'll try one rod size larger again while leaving the main jet alone for now.
Does this make any since? Or am I just wasting my time trying to get better mileage? PG.

 

What's the Cliff Ruggles book title? Always looking to learn. Never mind. Just googled it and first thing is his site: http://www.cliffshighperformance.com/

I put a small metal nail file (anything metal and about .015' thick will work) behind the pin to prevent over driving it.

Agree on Echlin kits, have also used Standard. Recommend a pleated paper filter. While I've never had a problem with the sintered bronze filters (stone), I've heard of those that had. I like the paper ones cuz you can cut them open and see if you are getting crap in your gas.

Might use the bracket and halve technique on rods. (old Navy gunnery talk) What it means is overshoot by going up several rod sizes and if it affects driveability, then drop back a couple. Just a thought. It will usually get you to your desired result quicker than if you just go up incrementally. Say the optimum rod size is five up from where you are. If you go up one at a time, you'll need at least six changes to get there whereas if you go up ten and drop five, you get there in two changes.

I agree with 78buckshot re: being afraid to touch them. I remember when I wanted to mess with mine on my '68 GTO (wished I still had that car ), everyone I talked to said they were hard to work on and real easy to screw up. Nothing was further from the truth. Also back in the late 70s, everyone was putting Holley spreadbores on. From what I could tell it had none of the good features of either carb. []

 

Had some time today so I changed both rubber fuel lines on both sides of the tank and installed the new vapor seperator. Jacked the car way up and barely had room but was able to change all 4 without droping the tank. No lines were broken but they were brittle. Took a ride and still have fumes but I'm convinced that it's just coming from the carb (good call 78buckshot)and not anything leaking. Also changed the gas cap (orngevette & schoon). 73shark-I'll leave the carb rebuild for another day. Thanks to everyone for the help, PG.