" Tip in " questions

[dougs69]

Hi, first some history...  stock 1972 Pontiac 350 changing over from 2 bbl to 4 bbl.
I have a 17059253 and called the shop and ordered pp spring, #73 jets, 44 rods and a kit.
Assembled it with the apt all the way screwed down... ran lousy obviously.
Then I got a 17058201 carb and assembled with the apt all the way screwed down again..

Then I realized I needed to buy your book to smarten up.
I bought your book.

well I put the 73 jets and 44 rods into the 17058201 carb and set the APT at 3.5 turns up from bottom.
Idles good but I have to really put my foot into the accelerator to get it to move...like its bogging.
The tip in did not rise rpm before choking out. I pulled off a vacuum line and it still didnt rise rpms.

so my questions are first will the parts i bought for the 17059253 carb also be good for the 17058201?
                                        which way should i turn the APT to achieve the rpm rise you decribe in your book?
       I did take measurements on the 17058201:  Idle tubes .053
                                                                               Idle down channel .061
                                                                               Idle air bleeds in body upper .070
                                                                                                                   Lower .077
                                                                               idle bypass air .071
                                                                               Main air bleeds air horn .120
                                                                                                         body .120
 The 17058201 carb is in much better condition, thats why I'm using that one.
Let me know what you think.  Thank you,  Doug

[73 Z28]

Doug,

Did you measure the idle tubes from the top of the carb? Normally they are pulled out of the carb and measured from underneath as the tube necks down.  Are you getting a popping sound through the carb when you accelerate like a backfire? Looking over your other specs, it looks like the main air bleeds need to be resized to .070 Also, I'd check the accelerator pump circuit, did you install a new pump seal and did you open up the accelerator discharge holes under the airhorn to .028?

Paul

[Shark Racer]

Agreed on the air bleeds, 73/74 jets are going to run VERY lean with those bleeds.

[dougs69]

well I called the shop and had .076 sent. I put it together with the .044 rods. WOW what a difference!!!! that old Pontiac really came alive!.  the problem I'm having now is I cant get the tip in set. when i pull off a small vac line the rpms rise which is telling me its running rich, even screwing the apt all the way down it still wants more air(rpms rise when I pull off a small vac line). The .044 rods don't have an actual step from the .026 section to the .044 section, they have a taper there and they don't have much of a taper on the larger section either, maybe a .001-.002.  also one of the mixture screws i can turn all the way in and it doesn't change the rpms. does that mean i need to remove the idle tubes and clean it out there? I'd really like to get it on the edge of lean for  fuel economy. any suggestions?
I have to say, between Cliffs book and this forum, wow what a fantastic resource!  Thank you Thank you,   Doug

[Shark Racer]

If you've never cleaned out the idle circuit you really should.

My personal recommendation is to get a pair of new tubes from Cliff, as I've yet to successfully pull a pair out. I'm an idiot when it comes to that particular task, though...

[dougs69]

Ok i just pulled out the idle tubes, they looked clean. no debris down in the bores. I will measure them tomorrow at work.  I did find that the base plate screws had loosened up, i guess from the gasket crush. Also I'm thinking I will order a new float, maybe the old one is getting saturated and thats how Im getting so rich . I will also measure the holes where the mixture screws seat (if it makes a difference). I checked the primary hangers and they dont look bent.
Thanks for the help, Doug

[dougs69]

you will have to forgive me, I'm learning as I go .I ordered new idle tubes.036 and new down channel restrictors to make it .052.  also knocked out the plugs in the body for the idle bypass air. Now i realize thet the accelerator pump discharge holes are about .063 Is this going to mess everything up? I'm begininning to think this old remanufactured q-jet was used on a sherman tank or something , any thoughts??

[Shark Racer]

Are you sure you're looking at the right holes for the accel pump? They're not a simple angle to get right the first time you go at them...

[dougs69]

well ...upon careful reexamination, i guess I wasn't looking deep enough into those bores, a flashlight revealed the true discharge holes located deeper beyond the counterbored section    Thanks for keeping me honest shark racer.