I am looking for Lars. I have a question on what size secondaries to upgrade to with the new 406. Lars, are you here?


-Justin

 

Yep.

 

Lars, After you answer the first gentleman's question, maybe you could answer mine. I have a freshly rebuilt Q-Jet #7041211. I am going to swap in a 454 4spd into my 72 SB auto. Will be using an intake off a 69 L36. What changes/tuning if any should be made to the carb because although it was not installed on my car, I am assuming it was setup for a 350.

 

Gage -
Your 7041211 carb is a 1971 350 1/2-ton GMC truck carb. In its stock form, it is jetted 74 jets, 42 pri rods, and "BA" (.057" short) sec rods. The 74/42 jet/rod combo is actually a pretty good setup, and I'd leave that in it (or set up that combo if it has been changed to something else). Just verify that your primary metering rods have .026" diameter power tips on them and not .036" tips. Replace the rods if they have .036" tips.

On the secondary side, remove the "BA" rods and install a set of "DA" (.044") rods.

Install a new NAPA 2-440 float and set the height to .375". Set your secondary rod hanger height to .640" as described in my Q-Jet Tuning Paper. Set idle mixture screws to 2 turns out from seated as an initial setting. Verify that the power piston in the fully seated position has about .030" of the brass collar protruding above the upper lip of the plastic retainer. Set secondary airvalve windup to 3/4 turn.

This should give you a very nice and responsive setup for your 454.

 

Yes Lars, but you haven't answered the most important question...

What kind of beer do you recommend to drink while doing this work???

 

I have learned this recently: anything that doesn't have the words light or lite printed on it.

 

Or 'XXX' unless you do not plan on working much past the 2nd beer.

 

Wow, Thanks for the info. I think I am better off sending it to you to perform your magic. Is your tour coming to Tx anytime soon?

 

He came here about 1½ years ago. Drank all the Shiner in Texas. The brewery called up and asked him that if he ever returns to provide advance notice so they can brew some extra! :

 

Lars, can you point to the plug that has to be removed to get access to the power piston. Hopefully a picture of a late model Q-Jet. If possible point where to test the power piston spring...Thanks

 

Lars,
I am putting a 406 in my 81'. It is the E4ME, but I'm confident I can get it to work just fine. It is a 10:1 CR with a set of 200cc dart cast heads, and a crane XE278. I have the stock rods in my carb now and was thining I should get something different for secondary rods. I believe the stock rods are CH and that I would need DA is what was suggested to me. Does that sound reasonable? And, I can't seem to find a chevy parts counter that can even get me secondary rods. Where does a guy get such a thing?

-Justin

 

Justin -
You have to have the part number for the rods in order to get them from GM - they don't have the letter codes. The following rods are still available from GM. If your local GM dealer won't order them for you (not that he can't...) you can get them from GMPartsDirect:

Code P/N Dia of Tip Tip Length
AX 7033549 0.0400 S
BG 7034822 0.0400 M
DA 7046010 0.0443 M
AH 7033812 0.0530 M
AU 7033655 0.0530 L
CV 7045984 0.0530 L
CH 7045779 0.0570 S
AN 7034320 0.0700 S
DP 17053531 0.0690 S
DR 17053659 0.0570 S

I suggest you use the CH sec rods - these are very good for a performance application. If you feel you're running lean, the DA rods are the next step alternative, and they may be beneficial for your combination - you just have to try them.

The following sec rods are available from Edelbrock under the noted EDL part numbers. You can get these through Summit or through your local NAPA dealer (even Checker Auto will get you Edelbrock parts):

CC #1950 (0.0303)
CK #1952 (0.053)
CL #1954 (0.067)
CE #1951 (0.0413)
AY #1953 (0.057)

So no more excuses on this "I can't seem to find a chevy parts counter that can even get me secondary rods" stuff... go get some rods, do some tuning, and drink some beer!

 

On 1975 & later Q-Jets, there is only one plug in the top of the carb - it's just forward of the choke airhorn. There are no other plugs. Just pull it. Test and/or adjust the piston through this hole. If you can't get the plug out, remove the airhorn and knock it out from the bottom before re-installing the airhorn.

 

Thanks Lars. Now I can go and tell my GM parts guy (the same one who told me he can't get them) that I have a part number and I want him to look it up.

-Justin