Q-jet tuning.... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Novaguy73 · 03-19-2006, 06:23 PM

I just rebuilt my quadrajet and i have no clue how to tune these. Im getting watery dark crap out my tail pipe and a small miss in the ignition. I put new plugs in it a few months back and they have about 5 total miles on them. Seems the miss gets lighter the more i bring the front adjustment screws on the bottom front of the baseplate out. I have them at like 3.5 turns each right now! Is this normal? What do you have yours at? Mine is a stock 72' 350 4 barrel Q-jet. Im also going to be puting a HEI and new wires on it maybe tomorrow night or sometime this next weekend if that makes a difference. The thing runs 100% better now and fires right off but i dont like the miss. Any pointers?

**tkeduk8r** · 03-19-2006, 09:13 PM

well i would invest in a good vac gauge, not to $$$$, and then find a timing light w/advance if possible and go from there... i adjust all mine with a vac gauge and seem to hav ehad really good luck with my qjets as a result... i am assuming that your motor is near stock, specially as far as the cam goes... if its running now, set your initiall timing w advance disconnected to about 8 deg BTDC, then run your screws all the way in till they just bottom out, and back out 1.5 turns each (this is prolly written in your carb rebuild inst too) then start the truck and adjust each equally in or out and find the nice happy place where you get the most vac... your needle shoudl be rock steady too, if it wiggles around you have some ohter internal prollems... nother idea for further tuning is o buy Doug Roe's book on qjets, learned alot from that and has been my biggest carb resource... then a matter of looking at your plugs every once in a while and fine tuning, but what i told you should get you inthe ballpark.. my 305 in my 74 C10 with 2004r is getting 16-18 mpg... any questions let me know...
--Mike

WRMZ71 · 03-19-2006, 11:03 PM

If you don't have a vacuum gage just do the same thing as listed above but listen to the motor. Go by about 1/2 turns on each one evenly and listen to see if the idle goes up. When the idle quits going up just turn them both in 1/4 to 1/2 a turn. That'll put you where you need to be.

68C15 · 03-19-2006, 11:06 PM

sounds to me like incomplete combustion. richening up the mix helps to cover the problem somewhat by merely giving it more fuel.double check the initial timing AND compression.

03-19-2006, 06:23 PM	#1
Novaguy73 Registered User Join Date: Oct 2005 Location: Waterloo, Ia Posts: 73	Q-jet tuning.... I just rebuilt my quadrajet and i have no clue how to tune these. Im getting watery dark crap out my tail pipe and a small miss in the ignition. I put new plugs in it a few months back and they have about 5 total miles on them. Seems the miss gets lighter the more i bring the front adjustment screws on the bottom front of the baseplate out. I have them at like 3.5 turns each right now! Is this normal? What do you have yours at? Mine is a stock 72' 350 4 barrel Q-jet. Im also going to be puting a HEI and new wires on it maybe tomorrow night or sometime this next weekend if that makes a difference. The thing runs 100% better now and fires right off but i dont like the miss. Any pointers? __________________ -73' Nova 350 5-speed 9"rear, Runs 11's drives anywhere... -72' C10 350 Auto 12 bolt, runs 19's?? drives to work!

03-19-2006, 09:13 PM	#2
tkeduk8r Senior Member Join Date: Apr 2001 Location: Alexandria, MN Posts: 1,462	Re: Q-jet tuning.... well i would invest in a good vac gauge, not to $$$$, and then find a timing light w/advance if possible and go from there... i adjust all mine with a vac gauge and seem to hav ehad really good luck with my qjets as a result... i am assuming that your motor is near stock, specially as far as the cam goes... if its running now, set your initiall timing w advance disconnected to about 8 deg BTDC, then run your screws all the way in till they just bottom out, and back out 1.5 turns each (this is prolly written in your carb rebuild inst too) then start the truck and adjust each equally in or out and find the nice happy place where you get the most vac... your needle shoudl be rock steady too, if it wiggles around you have some ohter internal prollems... nother idea for further tuning is o buy Doug Roe's book on qjets, learned alot from that and has been my biggest carb resource... then a matter of looking at your plugs every once in a while and fine tuning, but what i told you should get you inthe ballpark.. my 305 in my 74 C10 with 2004r is getting 16-18 mpg... any questions let me know... --Mike __________________ 63 C20 2WD, 230/SM420/4.11 73K 68 C30 dump truck, 327,SM425,4.56 66K original 68 C10 2WD SWB Stepper, 250/3-tree/3.73 66K.... Wifes 68 Buick Skylark Custom Conv., 350/TH400/2.56 In our family since '79 69 GMC 1500 SWB 2WD, 350/TH350/3.73 posi... 70 K10 SWB 4X4 4-sp,ps, pb, tilt, buckets, console, sliding back window (Need AC parts) WIP 72 Chevy K20 4x4 350/350/205/4.56 donor 72 Vette 350/M21/3.70 posi, triple black and super fast 84 Olds Cutlass Brougham 350/2004r/4.11 was Dad's

03-19-2006, 11:03 PM	#3
WRMZ71 Cause the Chicks DIG IT!! Join Date: Nov 2003 Location: Beaufort SC Posts: 509	Re: Q-jet tuning.... If you don't have a vacuum gage just do the same thing as listed above but listen to the motor. Go by about 1/2 turns on each one evenly and listen to see if the idle goes up. When the idle quits going up just turn them both in 1/4 to 1/2 a turn. That'll put you where you need to be.

03-19-2006, 11:06 PM	#4
68C15 blood type; Retumbo Join Date: Jan 2004 Location: next to my reloading bench Posts: 10,269	Re: Q-jet tuning.... sounds to me like incomplete combustion. richening up the mix helps to cover the problem somewhat by merely giving it more fuel.double check the initial timing AND compression.



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