Poor Fuel Mileage on 4.3 V6 with Quadrajet 17056250

[don3194]

Thanks again Cliff, I have a friend I'm going to sell the Marine Quadrajet to as a spare for his boat. I found a 7043202 Quadrajet for very cheap and just picked it up. I know you said 79 and up but I just got it on a whim hoping it could be converted to e-choke. Just wanted to ask if this carb can be converted.

[Cliff Ruggles]

No, the choke is on the intake manifold.

There are a few "conversions" available.  One involves replacing everything on that side of the carb with a modified bracket/e-choke, and the other uses parts from a 70-74 Olds or 73-74 Pontiac and the main casting has to be drilled/tapped for the pull-off bracket.

I've seen a third using a modified 75-up adjustable choke pull-off and putting a later hot-air choke housing on the side of the carb.  I'm not fond of any of those and it would be a LOT easier and less expensive to just source out a later model hot-air or electric choke carb right to start with.....IMHO.....

[Kenth]

To properly evaluate any carb it has to be at least renewed to factory specs.
Then it may need some help due to any symptoms shown at test drive.
A 4.3 Liter engine pulls less air than a 350 cui and the vacuum signal will be weaker making the power piston(s) rise at smaller pedal movements.
In the 17056250, early 1976 Olds 350 unit, the auxilary power piston spring is longer and stiffer than the regular power piston spring and may add more fuel than nessecary too early at low speed city driving for you 4.3 L.
The first attempt would be to use a weaker auxilary power piston spring, or cut to the same length as the regular pp spring.
I have done quite a few of these units, most of them got the auxilary pp system eliminated, 3-48 screw in jet and plug piston bore. APT is seated to start with and main air bleeds i bowl opened to .070". Most times #76-#77" jets with 52M rods are used. You always have the option to fine tune the APT. Also, an electric choke element makes the carb independent of intake styles.
HTH

[don3194]

Thanks again Cliff, I think I'll just go ahead and resell what I bought. Also thanks Kent, I'll try and see if I can make a lighter spring for the auxillary power piston, otherwise I am interested in possibly eliminating it all together. Are you aware of any other threads with more information on eliminating the auxillary power piston?

[Cliff Ruggles]

The aux PP and aneroid located APT carbs were short lived and for good reason.

Without going into great detail here I would NOT use one and source out a later APT model instead.

The 1975/76 models with that system just don't work well compared to the later models even after you block off the aux PP and single jet in the bottom of the casting.

I am NOT saying that you can't make one work, but it will never work as well anyplace as a later model set up with tapered metering rods that you can precisely position in the jets......FWIW......

[don3194]

Alright, I found another good looking cheap quadrajet and I think this is like one that you suggested. Its a 17059222, I don't think its off of a truck and couldn't tell if it was single airbleed or not, but some quick searches on google found people saying it was a good one. Thanks again.

[Kenth]

17059222 is a good unit.
I would start with mounting .050" inserts in the current .120" main airbleeds, keep the original #71 jets and 40K rods. Set APT at 4.5 turns up from bottom then use "tip-in" to check/adjust.
Opening the .033" idle tubes to .036"-.038" will help the engine idling.
Optional, if off-idle hesitation occurs, would be to open DCR´s from .050" to .055" and the .080" idle needle holes to .095".

[don3194]

Kenth are you referring to starting off on the 1709222? I just wanna make sure. Also if I do more reading up in Cliff’s literature will I find the meanings of some of the things you said. I’m not very familiar with Quadrajet’s or really any more recently designed automotive carburetor. I’ve only worked on a One Barrel off of a 1951 pickup before this one. I know APT, but I don’t know the “tip-in” method or DCR or how to do some of that stuff.

[Cliff Ruggles]

The modifications Kenth describes help the later emission calibrated carburetor get adequate fuel to the engine. 

Those are large MAB models and that particular one is set up pretty lean, but it's easy to tune and will work a lot better everyplace than the carb it is replacing.

If you call me at the shop next week I can set you up with what you need so it's pretty much "plug and play" for what you are doing......Cliff

[don3194]

Alrighty, thanks again Cliff.

[don3194]

Are there any detailed articles that explain the tip-in procedure for adjusting the APT? For that matter, where might I be able to find explanations on the proper initial settings for some of the adjustments that exist. Like the choke pull-off, the choke itself, APT, and maybe something else I am missing.
I have found some information floating around but some conflict and plain dont make sense, those did at least get me to a decent running engine with the 17056250, but on this 17059222, I want to have the best chance at getting it absolutely perfect.
Thanks

[Cliff Ruggles]

There are "basic" settings listed in the instruction sheets and tech manuals for the choke pull-off, fast idle specs, etc.

Even so it is best to make ALL adjustments on the engine as the factory specs only get you close anyhow. 

Here I use a mighty vac pump to apply the choke pull-off and set the open angle to make sure it doesn't choke out or flood the engine.  I also adjust the fast idle screw to about 1200-1400rpm's on the highest step of the cam at initial start-up.

The fast idle and curb idles settings can really only be done on the engine with it running.  None of this is fussy, but it may take several cold starts to nail down the ideal settings as the engine warms up quickly especially if you have a working exhaust crossover in the intake.......

[don3194]

Thanks Cliff. I guess I'm really focused on the APT and I know that can take a lot of trial and error, but is there a procedure called "tip-in" for adjusting APT? I've searched around online and only found people mention it but not explain what it actually is.

[Cliff Ruggles]

I just set them at 3.5 turns up from seated for initial testing.  Gently "tipping in" the choke from with the engine running around 2000rpm's on the fast idle will tell you if it's rich or lean.

If it's lean the engine will speed up and smooth out slightly.  If it's rich it will slow down instead.

That's really all a "tip-in" procedure is.  Make sure the engine is fully warmed up and heat soaked when doing this test......

[don3194]

Oh okay, thanks for explaining, that makes more sense.
I got it on the vehicle and started it up, at first it was running just fine, I was getting it warmed up to tune it and as soon as I started to reach in and adjust the idle mixture, a nice whistling/sucking sound started, the sound is very clearly heard from down the throat of the carb. It definitely is acting like a vacuum leak(idle is too high, and it responds well to a richer idle mixture), any idea where it could be coming from? When I get the chance to, I'll check my plug for the vacuum to the choke, but I haven't pulled it back off yet to look, but just thought I'd pick your brain for any idea on a sudden vacuum leak.

I did find another baseplate for it, this one actually had bushings put into it and its not worn out. The only reason I'm mentioning this is the possibility that they aren't compatible. The only difference I could note was two extra holes in the "new" baseplate that didn't exist in the original. I circled them in the picture.