Posted By: 1MYTGTX
Carter AVS mileage? - 07/12/11 08:37 PM
Took my first long trip on the highway using my newly restored "correct" 4640SA Carter AVS carb and got horrible gas mileage with it on the highway.....just a touch over 10mpg!
Averaging about 70mph/3100 rpm the whole way.
With my Holley 750 vac secondary carb with the HP main body, I was averaging about 15+ mpg......I think its time to switch back to my Holley....carb has been trouble since I put it on....have a pretty bad off idle stumble that I cant get rid of either....
Anyone else notice this with their Carters?
Wasnt looking to get any better mileage out of it....just an observation over my Holley
Posted By: dogdays
Re: Carter AVS mileage? - 07/12/11 09:22 PM
The original AVS had three-step metering rods and was a very economical carburetor. So, something is wrong with yours. It should equal or beat a Holley in mpg.
Others more expert than I will have to help discover what.
R.
Posted By: bschargerse
Re: Carter AVS mileage? - 07/13/11 02:05 AM
Chris,
I have the AVS from my '69 Charger on my Newport. Last year going to Carlisle I got close to 20mpg with the A/C off. But my car has a stock 383, with the iron '69 intake, and pertronix ignition, 2.76 gears. And I like to open up the secondaries LOL. I notice mine will stumble off idle if I floor it, but if I ease into it, then nail it, it's fine. I didn't check my mileage this year since the ignition was giving me fits. This carb sat for over 15 years, all I did was throw a rebuild kit on it and install it.
I was thinking maybe you are under-carbed based on the size camshaft you are using.
To add, I was just reading a magazine article from back in '03 that Mopar Muscle did when they built both a 383 and a 440 to Magnum specs. One of the things noticed on the dyno test on the 440 was that the AVS was becoming a restriction, since at WOT there was 1.4 in. Hg of vacuum. They bolted on a Holley 850 vac secondary carb, and horsepower and torque jumped by 10, and the peak HP was 200 rpm higher. This was with a stock cam, iron intake, and exhaust manifolds.
Just food for thought. I hope this helps.
Posted By: 1MYTGTX
Re: Carter AVS mileage? - 07/13/11 02:18 AM
Thanks Brian, I dont know why this carb is giving me troubles.
Made sure choke wasnt getting stuck etc....doesnt blow black smoke like its overly rich. Maybe I'm into the throttle more on the highway with this carb?
Actually checked gas tank to make sure I wasnt leaking anything!
Filled up before I left Carlisle and after 205 miles I'm on fumes!
Posted By: bschargerse
Re: Carter AVS mileage? - 07/13/11 02:31 AM
I have a new Holley Street Dominator intake sitting in the box if you want to try it. Bolt that on with the Holley carb you have; I think it would be perfect for that Engle cam. More HP and torque than the old CH4B, and a nice low profile. I know you were going for the stock look though. If you want to try it, I'll ship it to you.
Posted By: RapidRobert
Re: Carter AVS mileage? - 07/13/11 03:51 AM
Nothing you ain't prob already thought of (& tried) but I'd do the basics: float level/vac leak/jetting/accel pump (for the hesitation). I'm assuming you are on ported vac. It was good b 4 & no ch ex for the restored AVS? OE avs's are emission carbs & there was the constantly changing stringent emission std's that were put on Ma (& the others) back in the late 60's early 70's but they can run like a scalded cat. There's a serious prob somewhere that is making it hesitate and that may b something other than a garden variety weak AP shot (I'm sure you've checked) & if so it is screwing up your AF ratio & killing the mileage. Holler when you find something EDIT I'm assuming the springs are keeping it on the "cruise" step(s) at the vac level you are maintaining at 3100 rpm
I had a similar problem on the last AVS I used- put it on a 318, ran great, but a horrible off-idle stumble.
Turned out to be the kickdown linkage was not adjusted correctly (actually jerry-rigged is a better term). Switched to a Lokar cable set-up and was able to get ride of the stumble completely.
If he's stock- then I'd check to make sure the kickdown is adjusted, as well as all the things you have mentioned, but that's just part of doing a good 'tune' on a carb....
Enjoy!
CC.
Posted By: Paul_Fancsali
Re: Carter AVS mileage? - 07/13/11 07:57 PM
Chances are the gas loss was also due to the rapid evap Carters exp when parked etc also make sure you are not running the 101's I like them but the size will cause a large hole in you wallet from fuel
Posted By: SomeCarGuy
Re: Carter AVS mileage? - 07/14/11 01:55 AM
You've got an issue there someplace. I always get good mileage with the AVS.
Make sure the rods are moving freely and aren't off track. Vac leaks, etc.
Something is wrong if you got 5 MPG w/ no other changes.
Posted By: NANKET
Re: Carter AVS mileage? - 07/26/11 08:52 PM
Help us out with some info on you engine, what are the specs on your camshaft? Is it a stock type cam or a bigger one with low vacuum? what kind of fuel pump, how much pressure? Were you able to get any help from the carb restoration shop on this problem? AVS carbs generally work pretty well.
Posted By: superbeedave
Re: Carter AVS mileage? - 07/27/11 01:06 AM
If I were you first thing I would do is take the carb. apart just to verify everything looks okay and the correct jets/metering rods were put back in. Maybe check float. Is this engine a 440 or 383? Original jets sizes for that carb. are most likely too small for your setup. You could change the metering rods over to the AFB style. Just use the two step rods instead of the three and change the caps over to the AFB ones from the original AVS caps. Just my
Worth!!
Posted By: dogdays
Re: Carter AVS mileage? - 07/27/11 03:51 PM
But the three step rods give better fuel metering, why discard that?
R.
Posted By: Mapandjlp
Re: Carter AVS mileage? - 08/01/11 01:18 PM
I had the off-idle stumble with my AVS. Fuel pressure regulator set at 4.5 psi cured it with no other adjustments. Stock pump was giving 7 psi to the carb. Too much for the AVS.
with Dogdays point, it is a GOOD carb for performance/economy. First, you need a history of the carb and what it came off of. The jetting could be the problem, if it's wrong for the size motor you have. Air door and basic settings, also could be wrong for your motor too! Holleys' are good performers too, but they are also user-friendly. The belief is they're more so than Carter's. Contrary to POPULAR belief, AVS's, AFB's and TQ's are relatively easier! If you are patient and have the info at hand, they CAN be set up RIGHT! Also, recheck your ignition timing thoroughly, again for good measure!! 
