GM COMPUTERS

I PLAN ON SWAPPING OUT A 305 CARB MOTOR, WITH A 350 CARB MOTOR BOTH ARE 1987'S CAN I USE THE SAME COMPUTER WITH A SUPER-CHIP OR DO I NEED A COMPUTER FROM A 350  

if you are using the E4ME feedback quadrajet carb and going from 305 to 350... you need to find a real 350 carb... they all look alike... only the part numbers and jets are differnt.

i have hurd that the last iron block cad with the 6.0 feedback carb jets and metering rods  can be used on hotter 350s and still use the feedback carb......i think it was a 1981 deville california emission...

it has been a while since i took one of those carbs apart... i used to live and breath rebuilding q jets on normal cars..
i would imagine that if you had the proper ajusting tools and a scan tool or dwell meter you should be able to ream the primary jets out a tiny bit at a time until it is tuneable...  be aware that it took a 7 million dollar flow bench almost 20 minutes a carb to let the computer to ajust those carbs to run good and pass emission...

tools needed... torx bit sets... 1 inch fuel nut wrench, idle mixture screw flexable tools(2), float height dipstick.(this goes down the bowl vent to measure the amount of float height on one side and amount of travel on the mixture solenoid plunger in another hole through the carb top...4/32 max travel...  lean mixture setting tool, (this goes under the solenoid lever to ajust the stop height)    a tool to ajust the rich stop from the top.... another for the throttle position sensor height...
and a tool with a j hook to set the air bleed in the top cover...thexton makes most of them.. and most autoparts stores have the idle mixture screw flex tools in stock...
here is a link to a page with the hard to find part numbers for feedback  Q jet set up tools..
http://www.chevyasylum.com/tech/carbtool.html

wait... this is complacated... it is hard... .... this is not... it only takes some practice and understanding of what is going on....

since the primarys needles are commanded to  bounce up and down at 10 cycles per second... the computer can command them to stay up longer for a richer mixture or down longer for a lean mixture...

you can raise or lower the height of the needles travel to ajust the fuel mixture a bit to take up for worn motors...      

there is a green connector near the carb usually on a green wire that is not connected to anything..

that can be hooked up to a old style dwell meter set to six cylinder scale to read the amount of dwell the computer is commanding the carb to ***

with the idle mix screws set at 4 or 4-1/4 turns out each... warm the motor till operating temp ... (192/195F thermostat please)  read the idle dwell readings.. should be 28 to 35 degrees...  


bring the motor up to 2500 rpms... and the dwell should be  35 to 40 degrees of dwell...

you can raise the lean limit screw through the top of the carb... a double d tool not the air bleed with a screwdriver... the air bleed is for fine tuning..

this is like balancing on a ball... a little here and a little there...  and since you are changing the displacment  it is going to be way harder... which is why i think the orignal 350 carb or the 368/6.0L cad jets...


if you need more info let me know... i will be watching...    i would think that most of the better carb shops will have a proper jetted feedback carb that should bolt on without too much ajusting.. as long as you have installed all the necessory sensors...


and feedback carbs will not run well with any exhaust leaks before the oxygen sensor... fools the computer into thinking  the mixture is beyond it aibility to control.....

oh ... and be sure that all the computer grounds are properly installed...  clean and tight.... they all come out of the computer harness.....

and for others... the harness comes out with the motor... get under the passenger side of the dash... unhook the ecm... the connector to the dash side..  and the u shapped plastic lock on the plastic elbow...

the harness pushes straight out through the hole in the firewall.... lets you get all the ground wires on tight .. some are on the back of the heads.. and hard to get too...


the computer should work....

and .. when the 305's were properly tuned and the feedback carb ajusted they could pull down 22 to 23 mpg if you kept your foot out of it... i don't know what a properly built 350+ would ***  just don't go crazy in the cam department... feedback carbs like a lot of vacuum...  

THANKS FOR THE INFO, IT WILL BE MOST HELPFUL