Need help with recipe #1 No Idle

[mrk3cobra]

I bought Cliffs book and set my carb (17080229) to match recipe #1 in the book.Her is how I set the carb.
Idle tube .036
down channel .046
upper air bleed ,070
lower air bleed .078 was already at .078 cliffs recipe says .070
bypass air .080
mixture screw .090
Float 3/8"

The motor  is a 1986 Chevy 3/4 ton 350 with a edlebrock performer manifold and an edlebrock performer plus cam ( 204/214 @50 112 center line)

The problem is the motor will not idle below 1200 RPMS
If I remove a vacuum hose the motor does not increase, If I cover part of the choke housing I can set the idle to 800 RPMS and the vacuum goes up from 10 in to 15in of vacuum.Also when I do this (cover part of the choke cover)the ported vacuum for the EGR works correct with no vacuum at idle.

I have ordered new idle tubes if I need to try and increase the size more.

Any help on what to try  next?

[omaha]

almost seems like a vacuum leak.

[mrk3cobra]

I tested for vacuum leaks with a smoke machine and I have none. I installed an old edlebrock marine carb and the motor runs great. I can set the idle at 800 RPMS and I get 15in of vacuum.

[77cruiser]

Verify that you have the correct gasket between the body & baseplate.

[mrk3cobra]

Yes I have the correct gasket and I have replaced it twice.

I received my new idle tubes from Cliff today.

Cliff do you have any suggestions?

[Cliff Ruggles]

Re-size the lower idle airbleeds, or you will need much larger idle tubes, probably around .039-.040" to get close to recipe #1.

The "recipes" work, and are street, dyno and track tested.  These thing do however, involve EXACT precision.  Unless you duplicate all the sizes at every location, the fuel curve will not end up where it's supposed to.

Also keep in mind that the float height and fuel pressure have an impact on the results as well, as does the size of the float and the diameter of the fuel inlet seat.

Did you get a kit from us and set the float to exactly 1/4"?......Cliff

[mrk3cobra]

Cliff if I read your post correctly I will re-drill my new idle tubes to .039 and leave the lower air bleed at .078
and change the float level from 3/8" to 1/4". Does this sound correct.When I checked the fuel pressure it was bouncing between 4-6lbs. thanks,pete

[Cliff Ruggles]

You can attempt to compensate for the large lower idle airbleeds with a large idle tube.  I prefer to make them smaller, but a large idle tube and possibly more idle downchannel will help.....Cliff

[mrk3cobra]

I tried, the motor still has the same problem as it did in my first post.

Looks like I will throw the Edelbrock carb back on the motor, it idles perfect with the Edelbrock carb.

I give up on the Quadrajet I have torn it down 3 times and it runs the same as it did before I made any changes with the Quadrajet.

[Cliff Ruggles]

As we've mentioned many times, carburetor building involves EXACT precision.

The float level is set low, we recomend 1/4".

All of the items in the "recipe" are not within the recomended range.

The results may also be comprimised by other things, throttle plates not fully sealing (interntal vacuum leak), leaking at the primary throttle shaft, etc.

A low fuel level in the bowl, combinated with large idle airbleeds will not delviery the intended results. 

No mention was made if shaft bushings were installed, and or the size of the fuel inlet seat, size/type of float, etc.  All of these items effect the fuel delivery, and are well covered in our book.....Cliff

[mrk3cobra]

You can see from my post that I changed the float level to 1/4".
The float is new and is the smaller size.
I did not change any shaft bushings.There is no play in the shaft.

I followed the recipe exactly my guess is there is something wrong internally with the carb.
I know the throttle plates are not closed because if I cover part of the intake of the carb I can lower the idle screw and the ported vacuum ports work like they should.And when I do this I can increase the vacuum from 11" to 15".....

There must be a major leak in the carb...

[Cliff Ruggles]

No play at the shaft doesn't mean that it isn't sucking a ton of air by the shafts.  If you were to remove the shaft and gauge the bore and the measure the shaft, you will find it has considerable side play.  The factory tolerance was too much for my liking, so we install bushings in all units built here.

You have a lean condition, and need to add more idle fuel.  The .078" lower idle airbleed comprimises the "recipe" considerably.  I would resize it to .070", and open up the idle tubes a couple thousanths, and take the idle down channels to .052-.055".  You will see an immediate improvment.  If not, you have a big air leak someplace, either by the shaft(s) or throttle plates aren't fully seated at idle (common problem)....Cliff