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Old 06-15-2012, 08:52 PM
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New guy, need help - 1406 runnin rich

hey guys! new to the site and hadda join after all the info ive seen on here =]

ive got a 1980 suburban with a 1985 454 in it and i need help tuning the carb. ( stock motor i think>>> no lope )

i have an AFR meter hooked up to it and i have the idle set correct <<< 14.5-15.00 AFR at about 550/600 rpm>>>

my problem is this, at 1500/1700/2000 rpm the AFR drops to 12.5/13.5 and im getting bad fuel mileage. ( not like a 454 suburban will get 20 mpg or anything =p ) but going from 6 to eight would be nice, maybe even 10 8)



im not sure what to do, the carb is set to # 12 on the calibration chart but it didnt change the AFR where i wanted it =[ i have the weakest springs in it and still nothing

now being the motor has no emissions on it i have the vacuum advance set to the constant vacuum port on the carb. not totally sure if thats correct. fuel pressure regulator set to 4psi, 5 and on makes it unhappy

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Old 06-15-2012, 09:49 PM
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You need to get the calibration kit for that carb so that you can maintain the idle AFR as is and richen the midrange with the metering rods. You'll want a rod with a little larger diameter at the small end with the same as stock on the large end. The manual will explain everything. I would start by leaving the idle alone and going 3% leaner on cruise.
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Old 06-15-2012, 09:58 PM
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yess and yess

i believe im already at the 3% lean mark being im at # 12 on the calibration chart
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Old 06-15-2012, 10:03 PM
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i have the kit

ive topped out the options of the kit for going lean
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Old 06-15-2012, 10:38 PM
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Have you checked for vacuum leaks, also if the carb internals are clogged then it can prevent engine vacuum from acting upon the metering rods allowing them to stay open when they should be pulling towards closed (leaner)

Perhaps its time for a teardown soak and cleaning
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Old 06-15-2012, 11:05 PM
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shes cleaned

shes been cleaned many many times... i thought that was my problem so after about 5 cleanings i figured it wasnt the issue... is 2000 rpm out of a 454 making the secondaries open up ??? ive been curious when they start to open
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Old 06-15-2012, 11:06 PM
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no leaks

the truck idles fine and runs fantastic, i just wish it wouldnt run in the AFR that it does at 25/35 mph
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Old 06-15-2012, 11:29 PM
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jets

i have a set of .92 in the carter that im going to put in the burbans carb (secondaries)... this way if it leans out the 1700-2000 rpm range i know what the problem was =].

the current jets are the 95 via #12 on the calibration chart

correct me if im wrong guys. im just trial & error
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Old 06-16-2012, 06:26 AM
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Qute possible that you'll need a weaker spring to allow the rod to stay in the lean position longer. I would try using the #6 combination on the chart which is a .092" jet (1425) and .068" x .047" rod (1447) and a blue spring. It's possible that you're power mode is coming too soon and wreaking havoc with your cruise.
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Old 06-16-2012, 08:25 AM
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ill be

ill be pulling the suburban into the driveway today. lets see if i can make my issues go away =]

ill have to look and see if i have the needle you mentioned.
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Old 06-16-2012, 10:50 AM
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I read back on your OP. I don't believe 4psi is adequate. You should be at about 5.5 to 6 psi. If going to 5 or 6 makes it not run right then you have a needle leakage problem. You may want to kit that thing.
How is the float level set? What is your initial ignition timing?
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Old 06-16-2012, 03:25 PM
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Is this carb mounted on a factory Qjet manifold with a carb adapter?

can really mess things up.

reset the idle for best idle and idle manifold vaccuum as opposed
to a specific afr. It will be slightly richer than 14.7:1
It is not nessessary or ideal to set the idle afr to 14.7.
Idle quality is the priority.

Incorrect pri throttle position at idle will screw up the idle settings
and off idle calibration.
(throttles too far open or too far closed at idle.)
EG: too much vac advance at idle.

try ported vacuum and 10 to 14deg base idle timing.

At 1700rpm you are still primarily working with the idle circuit.
(the throttle is barely open)

you can see this using a mirror to view down the carb while raising the throttle speed.. watch the rpm and throttle angle where fuel starts flowing from the primary bosster venturrii.
This is the mains starting.
everything before this is the idle circuit.

The mains have not started working yet. Therefor the primary jet and metering rod will have little no effect on the off idle afr.
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Old 06-18-2012, 11:25 PM
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Hmmm

im wondering if the open spacer is my issue, but majority of the people ive seen with this carb/intake have the adapter i have =/
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Old 06-23-2012, 05:44 PM
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FOUND IT ! >>> I THINK =]

so i was able to put 92 jets in the secondaries in place of the 95 jets.

the afr went from 13.3 up to 14.4 at 2000 rpm, and at 2500 rpm it went to 14.7__14.8

i did however buy a 4 hole spacer and im going to replace it with the open one i have now. thankyou guys for the info, ill let you all know how the adapter works out and what it changes. then well all have the extra info =]
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Old 06-23-2012, 05:57 PM
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fuel pressure

my fuel pressure regulator is sitting at 5 psi. being many say 5>5.5 id say im in the ball park
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