Idle Bypass Air ??

[beertracker]

My idle bypass air holes are .113".   How big is too big?  At what diameter should I stop enlarging the holes?  I don't want to drill the holes too big and find I have ruined the base plate. 

Next I plan to change the float level from 1/4 to 5/16".

[429bbf]

bt are you sure its a carb problem?do you have another on to throw on?it just seem like you have other issues.i don"t know how pontiacs respond to changes . iv only messed with a pile of fords and chevys. your cam seems like it should be perfect for what you are doing .i would think you could idle it down to 600rpm or so .what happens if you turn the idle fuel screws all the way in ?does it make a difference? its hard to armchair a problem like this with a typewriter. I've been a heavy equipment mech for 40 years and work on quads for fun. its a a whole lot easier to fix when you can see it or hear it.if you were anywhere close i would drive over and help you fix it because that what i like to do solve problems.if i had a good pontiac carb id send it to you to try. fwiw

[429bbf]

bt  1 more question . iv read on here where pontiac uses a steel gasket and a paper gasket under the carb . is that the setup you have? do you have a major vacuum leak under the carb and you think its a carb problem?
?

[beertracker]

429bbf:

My gasket under the carb is a 1/4" thick fiber or compressed paper one.  It's the one Cliff sent me.  I never heard of Pontiac's using a steel and paper gasket.   My qjet has all cliff parts.  I installed his rebuild kit and performed recipe 3 based on cliff's input.

I think my fast idle problem is due to a vacuum leak somewhere.    I think the fuel dripping while engine idling at 1050 rpm or so and throttle plates fully closed is due to the engine wanting more idle bypass air?

I changed the float level from 1/4" to 5/16" and no changes in engine behavior.

I don't have another carb to swap out.    I have always had doubts about my Pontiac cast iron manifold concerning cracks.  My next step is to replace with a new e-brock performer rpm intake and see what happens.

Thanks for the offer of help but we are probably too far apart I am in Houston, TX.

[429bbf]

if your throttle plates are fully closed (idle screw backed out so far its not touching)it should not run ,unless you drilled 1/4 inch holes in the bypass, i agree with you and other folks that you have ether a bad manifold leak or something else wrong. i messed with my pickup today to see how low it would idle . it will idle good  at 500rpm and pull about 18-20 vacunm.its got a 17059212 carb on it .let us know what you find . fwiw

[beertracker]

If my fast idle is caused by a vacuum leak some where wouldn't adding idle bypass air only make the idle faster since the bypass air enters under the throttle  plates?

[429bbf]

yes you are correct in your thinking. but there has to be another problem . idle bypass the way i understand it . is a controlled vacumn leak . if all 4 throttle plates are indexed .spot on and totally closed . i still believe you would have to drill the holes a heck of a lot bigger to get it to run.fwiw

[beertracker]

The idle system is per recipe 3.  Wondering if I should consider changing it to recipe 2?  Does this make sense?  Recipe 2  would lean it out. 

The search continues.

[429bbf]

bt whats the part no. on your base plate? maybe i got an old one laying around here i can send you  that you can drill out as large as you like that way you don't ruin a good one for you specific carb.iv got a pile of junk carbs and if i have what you need i will give it to you.as far as your question about going back to receipe 2 cliff would be the one to answer that. he's worked on more pontiacs then I've seen.

[beertracker]

429bbf, lets hold off on the base plate for now but thank you for the offer.   I looked on the sides and bottom of the base plate and couldn't find a number.   Attached is a photo of the base plate it has two screw holes.

I did find a air leak at the air horn.  After adding a second gasket on top of the first the engine idle speed dropped to 790 rpm.  So I am making progress.   More work to do.

[beertracker]

I moved the nozzles slightly away from the venturi and retested and no changes it still drips fuel.   The nozzles won't move any further away from the venturi seems like they are bottomed out. 

Time for me to find a new hobby.  bt