Poor Fuel Mileage on 4.3 V6 with Quadrajet 17056250

[don3194]

So you guys may think I'm crazy for doing what I did, but its done and I'm having some problems with fuel economy. Basically the poorly designed fuel injection on my 1994 Oldsmobile Bravada failed so I found a manifold and installed this quadrajet I had lying around. I just used the walker rebuild kit from oreilly's to replace gaskets. So anyways my 4.3 quadrajet combo is getting only around 9 mpg in the city and 13 on the highway. I honestly believe I should be getting higher fuel economy, and my guess is that its dumping too much fuel for some reason. I also dont know if this quadrajet was from the 350 or 454 but from what I found it was off a 76' olds.

[Cliff Ruggles]

What are you using for a distributor?

[don3194]

I'm still using the stock distributor that came with the vehicle.

[Cliff Ruggles]

Not sure what they used for a distributor but it would need a distributor that has mechanical and vacuum advance to work correctly if you have converted it to a carburetor from a TB or Fuel Injection system.....

[don3194]

Okay. Well, I know it is a computer controlled distributor so it doesn't have vaccuum or mechanical advance. As far as I can tell it is advancing, but maybe not enough or too much.

[Cliff Ruggles]

I can't see what you've done but the original set-up would have had a different intake and intake system, TPS, etc which the ECM would reference for timing/fuel delivery.

To effectively complete the conversion you may need to install a distributor with mechanical and vacuum advance or engine efficiency and fuel economy will suffer.....

[don3194]

I can't see what you've done but the original set-up would have had a different intake and intake system, TPS, etc which the ECM would reference for timing/fuel delivery.

To effectively complete the conversion you may need to install a distributor with mechanical and vacuum advance or engine efficiency and fuel economy will suffer.....

Right now the ECM has enough input to properly advance the distributor, the vehicle drives and accelerates well enough, it just gets poor mileage.
I have noticed that when I go to start it, it smells like fuel and today I was just messing around with it, making sure I didn't have any vacuum leaks. Well, I pulled off one of the vacuum caps and the port was full of fuel. It was really only a dribble but I'm thinking this is related to my problem.

In the attached picture, my finger is under the port that the fuel dribbled out of.

If the image attachment doesn't work, I posted it here: https://imgur.com/a/O6Js6ki

EDIT: Keep in mind that I had just got done driving it when I pulled that cap off, so it was at operating temperature.

[Cliff Ruggles]

Your problems could be fundamental, starting with a poor quality rebuild kit with the wrong parts in it.  I'd go back in with one of my complete kits, correct float setting, check the PP hanger arms for being bent, leave access to the APT system for full control of part throttle A/F, etc......Cliff

[don3194]

Thanks for your input, I was thinking it would be something basic. How do I know which one of your rebuild kits to purchase? It looks like I have to choose between the Basic, HP and SR kits.

[Cliff Ruggles]

Get the SR rebuild kit.  It is a complete kit with all the parts required to do a complete/correct rebuild.

I would check the jets and metering rods to make sure they haven't been changed, modified, or just slam worn out.

I don't even look at them here, all carbs I get involved with get new ones.  One has to realize that these carbs have been out there for 50 years or so.  It's actually pretty common to see jets that have been drilled out to HUGE sizes and you wouldn't even know it unless you pin gauged them to check for size.......

[don3194]

Okay, thanks. I'm friends with a guy who owns a machine shop, I'll ask and see if he has any pin gauges. What size for the jets should I be looking at?

[Cliff Ruggles]

My listing skips that part number but it may be an early APT Olds unit with the auxiliary power piston. 

If it has the second power piston and single metering rod it will have pretty small jets in it.

Personally I avoid those here.  They had a very brief run and were abandoned for the far superior late style APT units, and for good reason.

1975-76 units with the APT in the left front corner (as viewed from the front) have fundamental issues related to the design.

The ones with the auxiliary power piston are the worse of the bunch.......Cliff

[don3194]

Sorry for the delay, It does have a secondary powerpiston with a single metering rod on it. I actually just happened to pick up a decent looking marine quadrajet, 17059286, for $20. Do you think I should rebuild the one I'm currently using or maybe try rebuilding the marine carburetor?
(At least I think its marine, the Division number 8 seems to be unclear.)

[don3194]

Sorry for the delay, It does have a secondary powerpiston with a single metering rod on it. I actually just happened to pick up a decent looking marine quadrajet, 17059286, for $20. Do you think I should rebuild the one I'm currently using or maybe try rebuilding the marine carburetor?
(At least I think its marine, the Division number 8 seems to be unclear.)

I thought about this overnight, and figured that I could probably turn around and sell this one and pick up a better automotive replacement. I just need an honest opinion, even though I think I know what it will be

[Cliff Ruggles]

I would NOT for any reason use or attempt to use a Marine Quadrajet for what you are doing. 

Get a later model side inlet Chevy carburetor preferably a single main airbleed model from a 1979-up truck application.  They are e-choke or will easily convert to e-choke, and very well made units.

Most Marine carburetors were divorced choke, no APT, crappy hinge pin/float design, and calibrated for heavy loaded most of the time vs light load, fuel economy, passing emissions, etc.

Most will not even have a vacuum port for the distributor vacuum advance either.  There are PLENTY of later model Q-jets out there and usually pretty inexpensive to buy as cores.  Avoid anything "rebuilt" or commercially "remanufactured".  I relatively clean and unmolested core will be best.......Cliff