ANOTHER......Question regarding my old Cad

[40]

Thought I'd start another thread so we didn't have to wade thru the other posts.

I decided to go thru all of the settings on the new carb before I started changing jets,metering rods etc. and when I checked the air/fuel mixing screws on the front of the carb I can affect the motor and can kill the motor by turning the right one closed.However,The left adjustment screw can be turned completely closed or turned completely open without any affect on the motor.I am thinking this is not correct and perhaps I have a defective carb?? Any Thoughts?? Thanks!!

[ragdol]

Sounds like the idle circuit is plugged, so it isn't working on the left venturi. You've got a one barrell carb at idle.

[wayne petty]

do you have compressed air available..

remove the idle mixture screw...    using a blow gun.. with a shop towel over the top of the carb.. so it does not spray gas all over the place... ON A COLD motor..

blow compressed air into the mixture screw opening.. then a shot of carb or brake cleaner.. then more compressed air..

you have a clogged idle air bleed...  so its pulling direct fuel into the idle circuit...

you might want to do both sides..

i am taking that this is the AFB/AVS carb...

warning.. if you have a quadrajet..   and even a carter copy.. please DON'T blow the carb apart with massive pressure and volume..   you can on a quadrajet.. if you screw this up .. blow the idle well plugs out...

the idle air bleed is removed in this image...    the drill bit is sticking through the idle feed restriction...




when setting up carbs...    most people tune for power..  by adjusting the main jets and metering rods...   changing power valve springs also...

flat spots are dealt with attempts to adjust the accelerator pump linkage or even the pump discharge nozzle...

here is another picture of the idle circuit including the idle transition circuit..



if you look at the upper circle.. you see the carb at idle.. with the idle mixture screw limiting the amount of fuel the engine can pull in..

if you look at the lower circle.. the carb is off idle.. but the airflow is not fast enough to start pulling fuel up and over the booster venturi and the main circuits..  

this is where major flat spots happen.. either the idle feed restriction/idle jet gets clogged.. or its TOO small to feed the motor displacement . so the engine leans out during transition..    no amount of main jet/ metering rods/ power valve springs is going to correct this problem..

~~~~~~~~~~~~~~~~~~~~~~~~~~~

when the idle air jet.. gets clogged..  there is no blending of the fuel that gets pulled over..  it just gets straight fuel..

if the idle feed restriction gets clogged..  there is NO fuel for that circuit..

please study the lower image..

i hope this helps...

and i know the image is NOT for an AFB/AVS.. the theory is the same on all carbs..  except for variable venturi...

[40]

Thanks guys....The carb is a new 1406 Edelbrock w/electric choke.The fuel filter is new so if there is something blocking the opening I'm guessing it is something left over from assembly.I'll pull both of those screws out and blow the openings out as suggested.......I'll let you know the results.

[40]

UPDATE!  Finally had a little time to work on the old Cad......removed both air/fuel screws and tried blowing air thru them.Driver side blew thru just fine.....Passenger side plugged tight.Talked to the folks at  Edlebrock and they seemed to think it was a machining problem...."Take it back to the store and exchange it" was the suggested remedy.That's what I did and other than a minor idle adjustment,it ran perfectly right out of the box....Problem solved!! Now......the bad news.....I just noticed an oil drip from the back of the motor    Just sealed everything up with new gaskets  :evil:  Oh well,that will have to be an issue addressed later......I've got a house to finish!Thanks for all of the suggestions/help!

[wayne petty]

i know that i am probably wrong.. but i seem to recall that the oil pressure switch is on the top rear of the block .. where its not only hard to get to.. but when it leaks.. it will be like a rear main seal leak..


please also check the valve cover gaskets.. by wiping behind the heads with a paper towel..    see if there is fresh oil on the back side..


that motor probably had a rope seal...

if it does.. and you intend on doing the pan and rear main drop.. i kinda think it might have an adaptor.. but..

with rope rear main seals..     a brass or copper  punch is used to pack the existing upper half a little tighter .. add some fresh sections to the sides .. and replace ONLY the lower half..    by carefully packing it in with a big socket then cutting long and again packing it in at the ends..

the rope seals will expand to fill the gap if you compress the ends ..

there is usually a SPIKE in the block to stop the seal from spinning.. perhaps its only in the cap..  

others will know more than i do on this issue..   i only did one of these motors about 28 years ago.. and its kinda foggy..  i did a lot of the front end work..

so i could be totally wrong..

glad they called for an exchange on the carb.. i actually talked to them years ago.. when crosley was having a problem with his..  i mentioned that perhaps the factory was getting debris or the wrong side idle feed restrictions in..    somebody there must have figured it out...

who would thing that dyno testing carb should be done from idle to 1500 rpms also..    not just wide open throttle..

sometimes i am ahead of the game..  sometimes.. i am just wrong..