I have a 67 Chrysler 300 with a pretty much "stock" 440 hi po motor in it (TNT,Magnum or whatever you want to call it). Earlier this month I switched from a dual quad set up (that was problematic) to a single Edelbrock Thunder AVS on an Eddy Performer dual plane intake. The dual quad set up had an Eddy Performer AFB primary carb and an original Carter AFB secondary carb.

The switch for the most part was a BIG improvement by there are several annoying issues I did not have before.

GOOD: Much better (TOO good) throttle response
Plenty of power throughout the usual street driving range, from mild acceleration to full throttle blasts. The car feels much more responsive and feels like a 440 TNT should.

BAD: My fuel economy has gone from bad to WORSE. I was getting 11 to 13 mpg for the most part...I'm down to 9.5 mpg and this is with pretty conservative driving.
The throttle response is like an ON/OFF switch. Hit the throttle and if you are not careful the car will JUMP! Same thing if you try to move the throttle by hand in the engine compartment. A slight movement yielda a HUGE change in RPM.
The choke is probably set too rich...she starts OK but then kinda stumbles unless I stick my finger between the choke and the air horn to let a bit more air in..Then she smooths out nicely.

Overall I am happy with the exception of the mileage which is frankly unacceptable for a street driven car. I have the jetting charts for both the Eddy Performer AFB and the Eddy Thunder AVS and the Thunder is jetted 1 stage rich as a starting point. So I can try changing the jetting on the primary side to one very similar to the Eddy Performer.


ANYONE's IMpressions or suggestions??

I would guess that your on/off throtle situation is due to the need for the proper accelerator attatchment.Edelbrock's #1481 Mopar throtle lever adapter should be used and will make your kickdown work properly.As for tuning-download the manual for your carb from Edelbrock's site.It can be done by reading the spark plugs (old school)but the preferred method would be an A/F meter.Standard is OK, wideband is ideal but pricey.Good luck.Your car should be capable of much better mileage. 16-18 highway is realistic.
Ron

You didn't say which Eddy Thunder carb your running. I am running both a 650 and a 800 on my cars and don't have the poor fuel economy. Part of it sounds to be your choke but I also think you are jetted to rich. Which carb are you running?

I'm running the Thunder AVS 800 cfm with electric choke, regular Performer dual plane intake and I'm USING the the Chrysler throttle adapter. I did not install this myself so I guess I should check the adapter to make sure it is attached/connected properly....I'm fairly certain it IS but a couple of replies I've gotten have asked if I'm using the Chrysler adapter.

I've used those carbs for years. I did an article on the new Edelbrock carbs back in 2003 when they first came out and I've used them on multiple engines since then.

The carbs work just fine. They are easy to install and easy to tune. They have a couple of limitations but work just fine on my 550 hp big block.

There isn't any need for the throttle adapter if you use the linkage kits that I designed.

Andy,

Where can I get the throttle adapters you designed??

Mopar73340,

Engine is stock and I will check what spring is in it...the carb is installed as "calibrated" by the factory. You say I should be using the oragne spring?? If I find there is a different spring in there, is this the one I should change to?? I DO have the calibration kit for the carburetor.

Any of the Mopar places carry my stuff. Mancini, Hughes, Mazzolini, Mayo, Magnum HP, etc.

What I meant by the "one step rich" statement is that my Primary carb previously was an Eddy Performer AFB, probably 600 or so cfm. I compared the jetting chart for the Eddy AFB with the jetting chart for my new 800 cfm Eddy AVS. From the charts, it appears that the base calibration for the Eddy Thunder is "one step rich" on the Eddy AFB chart.

Since my car ran pretty well and got fairly decent fuel economy when it was running solely on the AFB it seems resonable to assume that I can jet my new carb the same way and improve the fuel economy without hurting the performance.

As said I'd lean the choke a bit and change the metering rods to a pair .003 larger diameter on the "cruise" step. in the charts rods are listed as ie .073 x .042" with the 1st dimention being the "cruise" step. Double check your float(s) levels also.

You were running mismatched carbs on the 2x4??

Mopar73340

Are you in Bristow, VA??

I'm right down the road from you in Warrenton.
If you think you might want to take a look at my car sometime I could take a ride in your direction! Once the roads are dry...

I'll send you a pm

Here's some good news folks. Turns out Mopar73340 lives near-by me!! He volunteered to come out and take a look at the car. He switched the metering rods to one stage leaner, adjusted the choke, leaned out the accel pump discharge and leaned the idle mixture a bit. Car is a WHOLE lot more drivable now!! I'm sure with all the "leaning" fuel economy is bound to be better.

I've gotta give a big THANKS to him and to ALL those that are so willing to help a fellow Mopar enthusiast when in need. CHEERS!!