Q-jet tuning

[81_Chevy]

well since i have to wait till spring to put on my new carb and intake, im going to keep my q-jet for now to get some mpgs out of it.

right now i have a goodwrench 350, turbo 400, q-jet. all bone stock.

the last guy that rebuilt my carb, well he did a good job and got it running again, but he did not tune it very well at all. i think he just kinds slapped everything back together to make a few $ faster.

what are the different things i can do to get my carb back in tune? really just looking for mpg's. i know how to adjust everything like the air/fuel screws and the idle screw etc. and ive been messing with this carb for about 3 months now and i just cant seem to get it right. any tips and tricks to tuning these things right? or possibly close?

when my dad had this truck in springfield, mo where we used to live he found a guy that new these things like the back of his hand, its too bad there isnt guys like this around today, or atleast as many. all the new grease monkeys just plug in there little computer to tell them whats wrong lol,

anyway, thanks in advance for any info -Nic

[Jason S]

I'd first like to add, there are a lot of variables to look at for the Q-jet.  SO, you may want to get a book about Q-jet performance that you can have on hand to reference.

As for idle and the fuel mixture, you need a few tools to do this properly.  A dwell/tachometer meter (set for tach) to get the appropriate engine idle speed and a vacuum gauge.  The vacuum gauge will let you see when you have set the idle mixture screws to allow maximum economy at engine idle. 

As for other tuning, you can adjust the rate and time at which the secondaries will open and how fast.  This is where the book will come in handy.  Additionally, metering rods and jets can be swapped for performance or fuel economy.  If the carb is the stock Q-jet for the truck, it most likely was tuned for emissions and not performance or economy. 

These are just a few things off the top of my head, I'm sure others will add more when they get to read the thread.

[Damon23]

I'll add that you should get a vacuum gauge. It will be handy. The higher the vacuum the smoother the idle the better you are running.

[bake74]

I'd first like to add, there are a lot of variables to look at for the Q-jet.  SO, you may want to get a book about Q-jet performance that you can have on hand to reference.

    A excellent book on q-jets is the Haynes Techbook Rochester carburetor manual.  Book number 10230(2068). 
    Covers all different Rochester carbs, carb fundamentals, carb theory, overhaul and repairs.  Has diagrams, charts and pictures, modifications and even tells you how to match carb with intake manifolds, and other engine parts.