Powerplants => W72 => Topic started by: airpirate on April 26, 2017, 07:30:12 PM

Title: W72 quadrajet cast number?
Post by: airpirate on April 26, 2017, 07:30:12 PM
I have a 78 with the W72 performance option, I am having the carb rebuilt and need the vast number . Just curious if anyone would know that before I brave the snow and cold to check

Thanks
Title: Re: W72 quadrajet cast number?
Post by: jonathonar89 on April 26, 2017, 08:06:09 PM
17058263 I believe...17059263 for '79
Title: Re: W72 quadrajet cast number?
Post by: airpirate on April 26, 2017, 08:27:38 PM
Thanks partner!  Appreciate the help
Title: Re: W72 quadrajet cast number?
Post by: jonathonar89 on April 26, 2017, 09:02:48 PM
Thanks partner!  Appreciate the help

That was straight from the top of my head...no googling on that one lol
Title: Re: W72 quadrajet cast number?
Post by: airpirate on April 26, 2017, 09:24:56 PM
Impressive , I don't remember what I ate for breakfast:) ????
Title: Re: W72 quadrajet cast number?
Post by: TA78 on April 27, 2017, 06:54:14 AM
17058263 W/4 SPD, 17058266 for auto
Title: Re: W72 quadrajet cast number?
Post by: airpirate on April 27, 2017, 09:55:46 AM
Cool.    Thanks guys
Title: Re: W72 quadrajet cast number?
Post by: airpirate on April 27, 2017, 07:00:29 PM
Double checked mine it's
17058266.    Thanks again you guys
Title: Re: W72 quadrajet cast number?
Post by: Bandit818 on February 04, 2019, 11:19:54 PM
W72 carbs are 800CFM regular 400 carbs are 750CFM
Title: Re: W72 quadrajet cast number?
Post by: oldskool on February 05, 2019, 12:34:02 AM
W72 carbs are 800CFM regular 400 carbs are 750CFM

Sorry, but that is NOT correct !

All '76 & later Pontiac Q-jets are 800 cfm, including the 350 Q-jets, and even the 301 Q-jets. They are calibrated different. But, the throats are the same size & will flow the same amount of air. This also includes the 403 Olds Q-jets, and most of the Chevy Q-jets. The main difference in the 750 & 800 Q-jet is the primary venturi(throat) size. The larger venturis of the 800, will flow more air/fuel mixture.

Beginning back in the '60's, especially with Birds, Pontiac would limit the opening of the primary butterflies, in order to restrict flow & reduce power. That's why they rated the base '68 Bird 400 at 330hp, but basically the same base GTO 400 at 350hp. 

They probably did something similar on either the front or rear(or both) of the later Q-jets, especially on the smaller engines.

Of course, these restricted carbs can be modified for more flow & higher performance.
Title: Re: W72 quadrajet cast number?
Post by: airpirate on April 22, 2019, 04:09:48 PM
So my original Q Jet was toast, the bottom bowls corroded most likely from years of storage with ethanol gas (I'm told anyway). So I get a new (refurbished) carb, it sucked, brought it back to O Reilly I get another ( cast is for a 4 speed car) . My tech tweaked it, not running really right, put on a new HEI last fall, tweaked again. Finally got the car out , he spent most of Friday timing and adjusting the carb. Still not right, car runs smooth, but no low end like before and no kick down, runs more like my uncles 78 Caprice. smooth but no snap.

Was running rich always at idle, when you give it throttle, she bogs for a split second and then catches up, we leaned it back as far as it will go, still rich. The carb was sold as "adjusted for elevation", however I'm thinking the jets are too big for up here (between 5,000 and 9,000 ) think adjusting to smaller jets maybe the call?

Thanks!
Title: Re: W72 quadrajet cast number?
Post by: jonathonar89 on April 22, 2019, 05:09:55 PM
I’m doubtful Ethanol (grain alcohol) causes problems like most people associate it with but it may be possible with prolonged storage.  Yes, it may pull in or cause water absorption, but it’s a very clean fuel mixture if cycled.  In the future, Lucas and and others have made fuel stabilizers to store fuel containing ethanol.
Title: Re: W72 quadrajet cast number?
Post by: airpirate on April 22, 2019, 05:42:10 PM
The carb was original, the bowls at the bottom corroded where it was leaking fuel, no expert but my tech told me about the prolonged ethanol storage issue, I only use ethanol free 93 octane in her
Title: Re: W72 quadrajet cast number?
Post by: airpirate on April 23, 2019, 11:12:56 AM
not much help, but in response to your snotty reply, the car was restored in the early 90's and was parked inside as part of a private collection, not sure how much it actually ran. I acquired the car about three years ago and started addressing things that are a result of sitting for a long period. Since I owned the car I have been driving it and have ONLY used non ethanol 93 fuel (this is after replacing the old carb with the corroded bowls.) As mentioned, I do not have first hand knowledge on the corrosion issue, only told by my tech that has seen it happen in other carbs.
Title: Re: W72 quadrajet cast number?
Post by: Disco Man on May 20, 2019, 07:55:50 AM
airpirate,

You are 100% correct, gasoline with ethanol additives can be a big issue for older carburetor equipped cars especially when they are stored for long periods of time. The Rochester Quadrajets were all originally designed for 100% gasoline and never intended for gasoline with partial ethanol. Cliff Ruggles, the Quadrajet expert, mentioned to me about 2 decades ago that the original style Quadrajet floats are the most vulnerable Quadrajet part to gasoline with ethanol. These floats have a rubber compound that doesn't hold up well to ethanol. This is why Cliff on his Quadrajet rebuilds uses brass floats. I have found over the years through trial and error that adding STA-BIL Storage fuel additive evertime I add fuel to the tank of a car (that I don't drive often) seems to keep the ethanol troubles away since the gas doesn't deteriorate at a rapid rate.  It's when ethanol separates and absorbs water where the serious issues are encountered.  Also keeping a full tank of gas helps to keep moisture/water out of the tank.  My best advice is to use pure 100% unleaded gasoline as you mentioned however I live in an EPA mandated area where in the warm weather months all gasoline has ethanol added.  So far the Cliff Ruggles rebuilt Quadrajet (rebuilt in 2001) and STA-BIL fuel additive have been working to keep the ethanol blues away from my TATA.       

BTW, very nice 1978 TA that you have there.  You are very fortunate to have the W72/automatic combo.  For 1978 it's very hard to find that combo since not very many were made (I forget the exact production figure).  Pontiac stopped production in early-mid year of the 1978 model year so they only produced the 1978 W72/automatic combo for a few months.  Many years ago back in the 1990s, I stumbled across a mint conditioned 1978 Y88 with the WS6 package and W72/automatic combo.  I passed on buying the car, it was one decision I have really regretted especially since I have gotten older with health issues, driving an automatic car is much easier.

Also if you want more info on the W72 carb part numbers such as the primary jet, primary metering rods, etc. this info can be found in Mr W72's very informative 1977-1979 T/A 6.6 Historical Information document (link below):

http://www.originalho.com/1979TA/images/W72Tech_2004.pdf


_______________

Title: Re: W72 quadrajet cast number?
Post by: airpirate on May 20, 2019, 06:15:02 PM
Thank you Disco Man, very helpful response. I hated to part with the original carb but it was too far gone for a fix at the time. I do have new rebuilt carb with the cast number for a 4 speed car. as mentioned the car runs well, however I have it leaned back as much as possible and it still runs rich, I think the secondary's are really opening as they should.

I thought about sending it to Cliff but can't really wait 8 weeks to get it back summer is short up this high. Maybe I'll send it to him next fall. Thank you for the kind words on the car, I accidentally ran across while looking at another car and got pretty lucky.  Also love your TATA!

Enjoy the ride