Cliff's Quadrajet Parts and Rebuild Kits

And as promised,  here's a picture of what I've been doing to build a distributor advance machine,  at least as far as the distributor end of it goes.

 I used a protractor that I got from Harbor Freight because of its size, it should make it easier to see once everything is working.


 The base, or mounting for the unit is an old adapter tool that would turn a hand drill into a drill press,  it's an old Dayton that I've had for over 25 years, and I've almost thrown it out about a dozen times, but each time I think, Murphys Law will catch up with me if I do.

 If you think it looks a little odd, you're right, I turned the adjustable head upside down so that the drill points upwards, and the distributor will sit above it once I've figured out exactly how to mount it.

 Then I'll make a control board to mount the coil, any switches necessary, and the wiring needed to make it work.

 Once I figured out exactly how I would mount the protractor to the distributor, it was a matter of cutting and drilling everything for clearance.  I also needed to add a reinforcement to the protractor itself to steady it as once I started to spin the shaft the whole thing began to vibrate.  So a small piece of aluminum plate was all that was needed to stop the vibrations.

 I started by first removing everything from an old distributor housing so that I could determine exactly where the mounting screws are located for each part, as I wasn't sure which ones I would have to use initially.

 More to follow as things proceed. Just wanted to show my progress so far.

Hi Kenth

We appreciate the advice you shared a couple of months back about swapping throttle bodies on a Quadrajet to accommodate vapor cannister purge. As a follow up to you APT screw removal suggestion, today we successfully drilled out an APT screw without ruining the threads in the throttle body after spending weeks without any luck soaking, heating and trying to gently break the little screw threads free. So far we’re 1:1 in the APT screw removal challenge - two more throttle bodies to go!

My son and I are hoping you have a few moments to spare to look at the attachments we’ve included.

We’re looking for any suggestions you may have for improving a 4MC Quadrajet before we install it and road test it in a 1980 Olds Cutlass Supreme that my son and I have been building for the past few years.

The first attachment lists the specifications for the engine, induction, exhaust and driveline for the car.

The second attachment lists the current and original specifications for the 7040251 Quadrajet we plan to install on the engine next month.

The Quadrajet was modified following suggestions from Cliff Ruggles book a few years back. The current carb specs, as well as the original specs before it was modified are listed.

Based on an Innovate O2 sensor setup we installed on the engine last year, it appears the BB Olds will run at about 13:1 with  #69 main jets and #39B primary rods cruising at 18" vacuum, and almost the same 13:1 with 7" vacuum and the power system engaged. With #70 jets installed, it ran a tad richer into the mid-12s, especially with the power system engaged.

When you have time, could you please take a look at those carb specs and advise us as to any changes you feel will improve the Quadrajet before we install it and begin road testing.

Thanks very much.

DJ and Jed

 Yes, this helps.  I'm guessing that your readings are in distributor degrees because of the small numbers shown.

 I'll try to get some pictures of what I've done some far as far as the test distributor. Im also using an old drill press adapter, meaning it's a fixture that holds a portable drill in order to turn it into a drill press.  The distributor will sit at the top mounted above the drill itself.  Then it’s just a matter of outfitting everything that would turn it into a distributor tester.

 Rick

  Ok, just a bit of background info here, after doing all of my testing using the angle protractor to determine what the centrifugal advance each combo of plate/weight I've got on hand will yield.

 Remember i mentioned that the actual engine testing results were not the same as what I got on the bench.

 But comparing my bench results with the list that Kenth just posted, the differences are very slight.
 For 1 example I've tried on the engine,  Kenth shows that with a 370 center plate and number 139 weights, he got an advance of 25°.
 On my bench test, using the same plate and weights, I got an advance of 26°, which is just 1° off.
 However, on the engine, this exact same setup yielded only 20°, even when run up to as high as 4000rpm, falling short by 5 or 6° depending upon who's results you use.
 What gives? I realize that the springs can have an effect on both the rate of advance as well as the total available advance, I think. Is this correct?

 The next question, where would you get new springs that are not Chinesium garbage?

 I have multiple sets of springs, and there are differences such as the number of coils and the diameter of the wire itself. I'll try using the smallest ones I've got to see how it affects the total available advance.  This may be what I've been overlooking in the past. Any ideas?
 Rick

Here is some info that might be helpful: