17057547 Recipe #1

[oktorque]

The idle down restriction oem was .056.  I have the idle tubes set at .038.  Should I dial the idle down restrictions down to .046 as stated in book? 

The main in air horn and main body are at .070.  The idle bleed in main body is .070.  Idle discharge (mix) is .090.

Going on a ford 300 with 250 hp, mild cam, 17 hg vacuum.

[oktorque]

I meant to write 17059547.  I suppose I will set the down idle restriction at .047.  Would it be a problem to leave them at .057 as they were oem?

Cliff, does that sound good?

[oktorque]

I installed the carb. and could not get the idle down.  It ran at 1200 rpm, mix screws all the way in or out 3 or more turns.  Checked for vacuum leaks and none.  Checked for fuel from boosters, none.  Plates completely closed.  Where is it getting fuel and air from? 

[carmantx]

Did you modify the idle system to .038?   Wasn't it about .033 originally? 
I am not familiar with the original specs on that carb, but most earlier Buick quadrajets were smaller on the idle tubes, mains and idle circuits.  If you opened them up, may have gone too big.

[oktorque]

Hello.  Yes, at Cliff's suggestion I opened the idle tubes.  You're correct, the tubes were 34 originally.  Nothing is kept oem on this carb. 

[carmantx]

Ok, that's what I was thinking.  I do more Buick quadrajets than others.  So I have a pretty good feel for them.
You didn't add bypass air did you?
If your mixture screws have no effect, then you have too much in the idle circuits.  You might trying going smaller on the idle tubes for now. 

[oktorque]

I'm surprised the oem IDR was .056.  The bleeds were set small, yet the down restriction was so large. 

I wanted to get in the first recipe so I set the IDR to .046, and will set the tubes at .036. Before I change the tubes I'll run it.  I'm trying to understand the function of the IDR.  The tubes suck in fuel from the bowls and it travels up where air is introduced from the idle bleed, then travels through the IDR to the mix outlet.   So, why would Rochester install .056 IDR when the tube is .034 and the bleed is iirc about .062?? 

Very interesting.   

[Cliff Ruggles]

Not being able to get the idle speed down is usually a vacuum leak, or the throttle plates not fully seated.  That problem will need fixed first before any tuning can be successful.....Cliff