I recently purchased a complete Qjet #17087175 from my local junk yard. I am planning on cleaning and rebuilding it to use on my 75 while our local Qjet guru reconditions my original # 7045223. This reconditioning could take 3 days or 3 months depending on his obligations to racing customers. I have read all I can find on Qjets including Lar's papers and have a question concerning my swap. My original carb should have 72/46 jets and rods but the one I am rebuilding has 72/54 with .036 tips. Should I get the .046 rods for this carb or is there another alternative I should consider. Thanks in advance for any help.
Jerry

 

Someone has been inside that carb. Be sure that it hasn't been hacked. The 036 tips will make the idle much leaner( and the 54 rods will also effect the WOT), probably to meet smog regulations in later years. Look in Lars' papers for the rods/jets used in that carb originally for the actual area created for fuel flow at idle and WOT. If you can match those areas, you can change them. However, it's a maddening process because increasing the jet size to compensate for the 036 tip will also increase the WOT area. It's easier to find 026 tipped rods. The rod's lengths for early carbs is different than post 75 (?) carbs, and they cannot be swapped. However, the rods can be modified. Get some 3/32" brass tubing from a hobby shop. It will slide perfectly over the rod shaft. Use fine sand paper to clean the rod's shaft and a dremmel cut-off wheel to section the rod near (1/2" from) the "kink" where the hanger supports it. Slide a 1/2" piece of the brass tubing over the pieces to connect the two sections of the rod. Slightly crimp the tubing with wire cutters so that there is slight resistance to movement. Set the length of the sectioned rod from the tip to the "kink" to the exact length needed, and solder (I use a micro torch) and smooth the work area. I've done this to shorten and lengthen rods with excellent results.

 

After more research I have discovered the number of the junkyard carb crosses to an 85-89 Dodge truck. In Lar's tuning paper he states the Qjets were electronically controlled beginning in 81. I see no signs of any electronic controls in this carb so either it was converted to mechanical by someone or GM delivered a retro style carb for Mopar to use in these trucks.
In any event, The metering area of my original carb at 72/46 is 2.4096 at idle and cruise and 3.5406 at wot. If I keep the .054 metering rods and increase the jet size to .077 I will have a cruise, idle area of 2.36 and wot of 3.63
This 77/54 combo will be a little rich at wot and a little lean at cruise. The lean at cruise can be compensated for with the APT adjustment since the rod measurement is tapered from .054 to .040 at the beginning of the .036 tip.
I'm not sure I could do the cut and solder procedure and end up with 2 rods of identical length so I'm pretty much stuck with changing jets.
If I have this all wrong, someone please stop me before I do something stupid.

 

The numbers you posted are within 1% and should be OK. Check the fuel inlet fitting and threads to make sure it's compatible with your car. I'm far from being knowledgeable enough to determine if there are any significant differences between your old carb and the replacement. Place a call to Ruggles or email Lars.

 

I took JNB's advice a sent an E-Mail to Lars and he provided some very valuable information for my swap. Although the junk yard carb has bigger metering rods, he explained the difference in venturi design between the Vette carb and the truck carb. After he explained the principals to me he suggested using the truck carb with the existing 72/54 metering set up.
My idea to clean the scale inside was to boil all the metal parts in a 20% white vinegar/water solution let them sit for a couple of days and boiled them again. It is amazing what the mild acid solution did to clean the parts. I had to wait a few days for the carb kit. and took parts of 3 days to put everything back together while keeping the Mrs. happy.
In order to make it idle right I had to open the APT another 1/4 turn and open the idle mixture screws 6 1/4 turns. I tapped and plugged the top of the carb so I can make another 1/4 turn on the APT if I think it is necessary to close the idle adjustment a little.
Anyway, down the road we went tonight and it runs as good or better than my original carb. The water temp holds steady at 190 and the lean surge I had with my original is gone.
I would like to thank Lars for his help. His business is rebuilding carbs not helping shade tree mechanics like me. I have learned a lot this past week and hope I can pass a useful tip on to someone else some day. Now for my original carb, should I do it myself or send it to our race car tuner? His plans are to return my original to specs and recondition as well as rebuild it, should be good as new when he is done. My rebuild would be new parts only.

 

Good job on the setup and tuning!
Lars

 

Okay it's been 7 weeks and I finally got to pick up by reconditioned Qjet from the local guy. I guess race season ran into truck pulling season and therefore the delay.The truck carb I cleaned and rebuilt did it's job admirably and I am happy I decided to go that route. Without my friendly junk yard and an Autozone kit my ride would have sat in the garage the whole time. The first thing the guy told me is the 7045223 carb from my 75 is an 800cfm and not a 750cfm. Not real surprising but a happy turn of events. Anyway I did the swap back to my original today and the beast started up after a few turns and came to life. The fast idle was a bit too fast for my taste but that can be taken care of. After it warmed up and got down to curb idle I adjusted the idle mixture to top out the vacuum reading to a steady 18Hg, adjusted the curb idle to 950rpm and let it run for 10 minutes or so. When I took it down the road It purred like a kitten and the lean surge was completely gone. When I romped on it at the first stop sign, all I can say is holy bat crap Robin! Even with 3.08's pushing me I was glued to the back of the seat hit 2nd and broke the tires loose. Remember the grin on your face when you bought your first hotrod? Yeah baby, I'm there again.
Jerry