carb tuning
Thread Starter
Instructor
Joined: Mar 2008
Posts: 221
Likes: 0
From: Farifax Station VA
carb tuning
I have been searching the forum for some guidance on how to tune my Q-Jet, after that I am going to attempt to set the timing. I just got my carb back from carburetorUSA, in NJ, it is now running rich, so I need to adjust it, but don't want to screw it up--at least it will start?? any help woud be great. 1977, auto, TH350, the carb I belive is off of an '84 truck...the jets may be a little bigger than stock. thanks.
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
Start car and warm fully.
hook up a vacuum gauge to manifold.
adjust idle to specs with idle screw.
Verify timing is correct.
adjusting mixture screws a little at a time trying too
turn each one equal amounts try to achieve the greatest
vacuum reading all the time readjusting idle screw to spec rpm.
then a stock setup would be, turn in both mixture screws a little
to get a 50 rpm drop.
this is known as the lean drop.
hook up a vacuum gauge to manifold.
adjust idle to specs with idle screw.
Verify timing is correct.
adjusting mixture screws a little at a time trying too
turn each one equal amounts try to achieve the greatest
vacuum reading all the time readjusting idle screw to spec rpm.
then a stock setup would be, turn in both mixture screws a little
to get a 50 rpm drop.
this is known as the lean drop.
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
I have been searching the forum for some guidance on how to tune my Q-Jet, after that I am going to attempt to set the timing. I just got my carb back from carburetorUSA, in NJ, it is now running rich, so I need to adjust it, but don't want to screw it up--at least it will start?? any help woud be great. 1977, auto, TH350, the carb I belive is off of an '84 truck...the jets may be a little bigger than stock. thanks.
You want to re jet?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
You paid for a rebuilt carb for your car and they didn't set it up for your engine? 
That can be a problem as there are several areas of concern when the carb is running 'rich': jets and/or rods and/or power piston, etc., etc.
That can be a problem as there are several areas of concern when the carb is running 'rich': jets and/or rods and/or power piston, etc., etc.
Thread Starter
Instructor
Joined: Mar 2008
Posts: 221
Likes: 0
From: Farifax Station VA
your right...and now I am having somewhat of a hard time trying to find someone who can set it up for me in Fairfax, VA. Adjusting the idle mixture seems pretty easy...but it really blows smoke under higher acceleration...how do I adjust this?
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
What color smoke, black?
Are you running stock motor?
Can you get the carb place to give you specs on what they gave you and why?
Now a days there are systems using O2 sensors that will guide you.
Back in the day, I would go to the library and get all the jet and power valve and needle specs for a motor that was similar to the motor
I was building. I.E. LT1, L88, ect.
Thread Starter
Instructor
Joined: Mar 2008
Posts: 221
Likes: 0
From: Farifax Station VA
Yes the smoke is whitish colored. you can smell the gas. the jets maybe too big...is this something I can change easiley? Can I change them with the carb on the car, or do I have to remove it?
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Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
water 
Rich = black smoke
Oil = blue smoke
water/coolant = white smoke
Could it be light blue?
Are you using/losing oil or water?
sorry guy, time to pull plugs, compression test and check
radiator for exhaust gases.
Last edited by calwldlife; Jul 3, 2009 at 05:38 PM.