carb questions

[Cliff Ruggles]

The operation involves EXACT precision.  If you are off any at all the seal will not fit evening against the seat at the bottom of the threads and it will leak.

I have genuine heli-coil taps for both 7/8"-20 and 1"-20 threads and have installed thousands of heli-coils into Quadrajet and 2-Jet castings.

It is actually pretty rare to see the 1"-20 (1972-up) Quadrajets stripped out.  That only happens when someone cross-threads the fuel filter housing.  Attempts to install self-tapping fittings may remove needed material required for the heli-coil tapping operation.

I'd have to see the carb to know if it can be repaired or not?....

[old blue 75]

Have you ever made or thought of making a new fitting and tapping it 1 1/16-20?
I spent 8 years standing in front of a lathe so making a new fitting isn't the end of the world.
My thinking is to tap it 1 1/16-20 then at the same time take a 1" end mill and re face the seal
surface square to the threads (.003 to .005 thousands).

[Cliff Ruggles]

I suppose with enough effort anything is possible.

Unless it were a really valuable Ram Air, HO, Super Duty, Stage 1, W-30, Cobra Jet or something difficult if not near impossible to replace I would just walk to the core pile and get another casting vs spending many hours on that type of repair.

Machining a fitting wouldn't be that difficult until you got to the inverted flare deal.  I'd most likely at that point just tap it for NPT threads and install an adapter fitting.

I have the equipment and skill sets, Military trained and I used to make parts when we needed them in the machine shop on board ship when were on deployment, thousands of miles from port and no hardware or parts stores floating around out there anyplace.  Where I typically fell short on those sort of jobs wasn't making the part, it was the heat treating if/when needed........

[old blue 75]

Cliff thank you very much for your service. Yes I would agree aboard ship It would be tough to heat treat any thing. About the only thing I can think of would be small parts made from o-1 with a torch
and oil.
 I under stand it would be easier to use a different carb but Here in Michigan the junk yards ran out of vehicles with carbs on them many years ago. And with the covid crap swap meets have been few
and far between. I will have to think on this while I work on other parts of the truck.

[blazer74]

Another .040ish in the hole SBC. Rebuilders flat tops. I’m not alone.

[old blue 75]

Yup you have to pay attention we ordering pistons. Stock sbc 350 is 1.560 pin height, there are 1.540 and 1.550 pistons out there. I figured this out to late.

[old blue 75]

Finally got back to this carb.
I found a 1 1/16"- 20 tap on ebay and made a replacement fitting ( and made a inverted flare cutting tool to finish the fitting).  Taped the casting and refaced the seal seat. I did a pressure test with a plugged seat and air hose hooked to a short piece of fuel line. At 20 psi did not see bubbles in my soapy water. Is this a good enough test or is there a better way?

[Cliff Ruggles]

20 psi and no bubbles/leaks it will be fine...

[old blue 75]

Ok cool.
Moving on, I have the primary shafts bushed but will need screws.
 I measured the primary metering rods and they seam to be the 74 back
long style. The part number says 1975. Was 1975 a transition year?
The primary rods have flat spots worn on them, I did not see them on
your site do you not have them?
Here is info on the carb.

Idle tube .044
Idle down channel .053
Upper idle air bleed .092
lower idle air bleed .063
Idle bypass .097
mixture screw hole .074

Air bleed main body .119
Air bleed air horn .120
main jet .071
primary rod .026

secondary air bleed .026
Secondary air flap 1.390
Accelerator discharge holes .053
Secondary accelerator wells .034
J hanger CP rods

Also what is the life expectancy on choke pull offs.
The one I took off is good but I have had it sitting on the
shelf for 10 yrs plus and who knows how long it was on there
before I got it?

Thanks

[Kenth]

7045214 is a 350 HD Truck 4M Quadrajet.
This unit have 39B primary rods from factory.
Only M4M uses the shorter primary rods.
Check the "accelerator discharge holes" or secondary POE again, the restriction is located a bit in from the .053" exit.
SB Chevy Qjets uses .042" restrictions, most BB and some HD SB units uses .035".

[old blue 75]

Ok rechecked the discharge holes you are correct it is a .042.

[Cliff Ruggles]

I stock primary metering rods for all q-jets, plus have close to 10,000 #3-48 black plated screws for the primary shaft.  If you don't see what you are looking for on the site best call to place an order.  I'm here 7am-4pm M-F EST.  Call volume is heavy, so if I don't pick up leave a good number and I'll call you back.......tks....

[old blue 75]

Ok will do.

[old blue 75]

Cliff what tuning modifications should I do to this carb?
Or would you rather discuss it when I order a kit?
I for sure need new idle tubes, kind of mangled them
getting them out.

Thanks.

[Cliff Ruggles]

I'm here 7am-4pm M-F EST.  Call me when you get a moment, saves a lot of typing....tks..