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Old 01-02-2003, 03:43 AM
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Post Demon Jetting

I just built a 383 sroker motor with the following:
383 stroker from Eagle
10.5:1 compression
AFR-195 CNC ported heads with severe duty valves
Comp roller cam (Adv.282*/288*) 230*/236* @ .050", 544/555 lift w/1.6
roller rockers, 110* l/s
Hooker Ceramic Coated Super Comp headers
Eldebrock RPM Air-Gap Intake
Demon 750 carb (vac secondaries)
TCI-700R4 transmission

It is rich at idle and fouls the plugs
I I fashioned this motor after one of the magazine build-ups and they used 81/88 jets.
I down to 73 on the primary side and it still runs rich (black sooty plugs)
The carb came stock was with 76 on the primary side
I’ve replaced the power valve with no improvements.
If I keep “leaning” it out, I feel that something else is wrong
Any advice?

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Old 01-02-2003, 08:00 AM
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the idle circuit is controlled
by idle mixture screws and air bleeds not you
jets, there are 3 circuits primary, secondary,
and idle. the best way to tune your carb is
with an air fuel mixture gauge wich requires
an 02 sensore, weld in exaust bung, and gauge.
then you would first adjust your idle screws
(either 2 or 4 depending on carb) (adjust them
evenly), then you would hold open your primarys
(part throttle) to get a reading on the primary
circuit mixture-then you would adjust accordingly
finaly you holdsecondarys open-this is probably
best done on the freeway- get a reading and adjust
accordingly

the cheap way to do this is with spark plug
readings (less accurate)

do a reading for each circuit (3 sets of plugs)
dont let the vehicle run on the circuits you
not testing in other words for idle circuit-
let it idle for a long time, turn it off and check the plugs - for primarys hold part throttle for a long time then check plugs - then wot for secondarys.

one trick I use is to hook a vacuum gauge to
manifold vacuum and start one screw at a time
i woul start them all @ 2-2.5 turns out, then
,starting with one screw lean it out till
vacuum just starts to drop then back it back off
1/4 turn, notice about where the screw is(how many
turns out) then do the same vacuum adjustment at all
four screws (demon carbs have a 4 corner idle
circuit (i think) ) the other 3 screws should be real close to the first one you set.

i believe demon carbs have screw in air bleeds-
don't touch them unless you cant get the idle
to lean out- if that is the case start stepping
up the air bleed size ( i wouln't mess with
them if you can help it)

try the vacuum adjustment then do a spark plug
reading on the idle circuit then adjust more
if necessary.
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