Carter Thermoquads ~ 'More General Information'
this guy hit the nail. truth is, what he did with the air bleeds/idle feed restriction was illegal for car manufactures to do from 1972-onward, the cars could not be sold legally in USA. however, prior to 1972, this is how all the carbs were set up as the industry standard. that's just how lean everything got after '72. an early CS carb has the richer metering already. the later CS 9800 series would also be somewhat richer than the OEM carbs. 12.6 at idle, 14.1 at cruise is dead nuts on. it doesn't get much better than that. I added the highlighting:
ThermoQuad tuning at Cruise
ThermoQuad tuning at Cruise [Re: RayR] #2358872 08/24/17 12:36 AM
chargerjoert
Joined: Sep 2015
Michigan
What list number thermoquad are you running and what is the top casting 4 digit number (near the fuel inlet, like 2124 etc...)?? Thermoquads were tuned very lean for each application and they got worse (leaner) as the years went by. Changing IAB's, IFR's, Idle air bypass passages, and adding bleeds to lean the circuits. Not to mention all the emissions junk that was added. Also, how many turns out are your idle mixture screws (from lightly seated closed)?
I do not have, or ever used, a lambda sensor for AFR. But I have used a vintage Heathkit Co meter. My experience has been the AFR will (and should) get leaner as rpm goes up (say in Park, and idle to about 3,200 rpm). I have not actually driven on the road with it to get data.
For the gasoline here in the states (E10) I find more idle timing helps a lot. Reduces coolant temp and reduces the exhaust smell. And that big blocks do not like to idle or cruise on lean mixtures. But I also have a single plane intake manifold. My cam (xe268) generates about 16 in-Hg at idle in park.
My thermoquad is a modified earlier 6500 series with a 2124 top casting. This casting in stock form has IAB @ 0.038" and 0.034" IFR. I typically run 18 to 21 degrees at idle and 32 total. The modifications to the thermoquad cruise circuit (currently) is IFR's @ 0.040" and IAB's have 0.011" guitar wire in the holes. And idle air by pass holes drilled to 1/8". Idle mixture screws are about 2.25 turns out. Modify at you own risk (and I would go in small steps to see what works for you). My car runs nice and cool and does not stink. My Co meter reads approximately at idle 12.6 and goes leaner to about 14.1 at 3,000 rpm (in Park). Meter could be off, as I suspect the real readings might be slightly leaner.
this guy hit the nail. truth is, what he did with the air bleeds/idle feed restriction was illegal for car manufactures to do from 1972-onward, the cars could not be sold legally in USA. however, prior to 1972, this is how all the carbs were set up as the industry standard. that's just how lean everything got after '72. an early CS carb has the richer metering already. the later CS 9800 series would also be somewhat richer than the OEM carbs. 12.6 at idle, 14.1 at cruise is dead nuts on. it doesn't get much better than that. I added the highlighting:
ThermoQuad tuning at Cruise
ThermoQuad tuning at Cruise [Re: RayR] #2358872 08/24/17 12:36 AM
chargerjoert
Joined: Sep 2015
Michigan
What list number thermoquad are you running and what is the top casting 4 digit number (near the fuel inlet, like 2124 etc...)?? Thermoquads were tuned very lean for each application and they got worse (leaner) as the years went by. Changing IAB's, IFR's, Idle air bypass passages, and adding bleeds to lean the circuits. Not to mention all the emissions junk that was added. Also, how many turns out are your idle mixture screws (from lightly seated closed)?
I do not have, or ever used, a lambda sensor for AFR. But I have used a vintage Heathkit Co meter. My experience has been the AFR will (and should) get leaner as rpm goes up (say in Park, and idle to about 3,200 rpm). I have not actually driven on the road with it to get data.
For the gasoline here in the states (E10) I find more idle timing helps a lot. Reduces coolant temp and reduces the exhaust smell. And that big blocks do not like to idle or cruise on lean mixtures. But I also have a single plane intake manifold. My cam (xe268) generates about 16 in-Hg at idle in park.
My thermoquad is a modified earlier 6500 series with a 2124 top casting. This casting in stock form has IAB @ 0.038" and 0.034" IFR. I typically run 18 to 21 degrees at idle and 32 total. The modifications to the thermoquad cruise circuit (currently) is IFR's @ 0.040" and IAB's have 0.011" guitar wire in the holes. And idle air by pass holes drilled to 1/8". Idle mixture screws are about 2.25 turns out. Modify at you own risk (and I would go in small steps to see what works for you). My car runs nice and cool and does not stink. My Co meter reads approximately at idle 12.6 and goes leaner to about 14.1 at 3,000 rpm (in Park). Meter could be off, as I suspect the real readings might be slightly leaner.