440 w/ AVS stumbling at cruising speed.

[dvw]

Pin vice in and hand twist it. What's the big deal? No different than drilling an air bleed. I never did the math. But if the calibration was spot on from the factory, maybe both should be adjusted. Oh wait. There were prehistoric emision band aids in the late 60's. And we're now 50 years later with cam timing that isn't factory. Neither is the fuel. Lets stop being so picky and just help this guy make it run decent.
Doug

 

[Dave6T4]

My '67 R/T always had a stumble/surge at 50-55 mph. I replaced the original AFB with a friend's AVS, but the surge continued. I played with rods and jets on both of these, thinking the engine was running lean at cruise. I eventually put a new 750 cfm. Edelbrock on it, but the surge remained. I finally put a different Mopar electronic distributor in the engine, and the surge disappeared, as well as a low speed stumble. On the last two tanks of gas, it looks like I have picked up 2-3 mpg., as a bonus. There was definitely something wrong with my old distributor.

 

[lewtot184]

Short answer is: yes. But to INCREASE the diameter of the idle fuel metering orifice from 0.031" diameter to 0.035" (or some other diameter +/- 0.001" determined quantitatively) can be done but how? Through the use of number drills (#61 - #80) or reaming or ??. Not "air bleeds" just the one that controls the VOLUME of air introduce to the idle fuel circuit of the booster venturii. By making the air bleed smaller, yes, the differential pressure signal will increase, allowing greater fuel flow.....thereby increasing the Air/Fuel ratio generated....Boyle's Law applies.....in proportion to cube of the flow. If you've solved your issue, congrats.....because the orifices involved are small, the utmost care and accuracy is necessary to accomplish the task.....
BOB RENTON

i use drill #'s 61-80 to clean and enlarge (if necessary).

 

[lewtot184]

My '67 R/T always had a stumble/surge at 50-55 mph. I replaced the original AFB with a friend's AVS, but the surge continued. I played with rods and jets on both of these, thinking the engine was running lean at cruise. I eventually put a new 750 cfm. Edelbrock on it, but the surge remained. I finally put a different Mopar electronic distributor in the engine, and the surge disappeared, as well as a low speed stumble. On the last two tanks of gas, it looks like I have picked up 2-3 mpg., as a bonus. There was definitely something wrong with my old distributor.

i've found that trying to add fuel for a cruise surge when the timing is too far advanced doesn't help much if any. i've found thru the years that a carb can't be probably adjusted or calibrated if the ignition timing is screwed up. always fix the ignition first.

 

[RJRENTON]

i use drill #'s 61-80 to clean and enlarge (if necessary).

I'm aware of the physical mythology of enlarging the orifice...thru the use of a pin vice and #61-#80 drills....but how do you REDUCE the size of the orifice, especially if it's in an aluminum component? Just asking....
BOB RENTON

 

[Dave6T4]

I'm aware of the physical mythology of enlarging the orifice...thru the use of a pin vice and #61-#80 drills....but how do you REDUCE the size of the orifice, especially if it's in an aluminum component? Just asking....
BOB RENTON

JB Weld? Or does gasoline affect it?

 

[lewtot184]

I'm aware of the physical mythology of enlarging the orifice...thru the use of a pin vice and #61-#80 drills....but how do you REDUCE the size of the orifice, especially if it's in an aluminum component? Just asking....
BOB RENTON

i haven't jumped thru the alum hoop,...yet. brass can be soldered up and start over. i have had to start over a few times,...lol! it's really not a big deal but finding some reference material to help you and going in incremental steps keeps the whole process honest.

 

[RJRENTON]

i haven't jumped thru the alum hoop,...yet. brass can be soldered up and start over. i have had to start over a few times,...lol! it's really not a big deal but finding some reference material to help you and going in incremental steps keeps the whole process honest.

YES....i've soldered brass b4 using either a: 60%-40% or 50%-50% or a similar blend of flux core electronic solder....and NEVER an acid flux solder. A silver solder could be used like Silfos 95% - 5% silver copper alloy..,stronger but it takes a higher temp to melt...~ 1000° F.. it's just be careful and not needing to reduce the size of the orifice.....
BOB RENTON

 

[Geoff 2]

With a larger than stock cam in this engine, it is exhibiting the typical leanness that you would expect from using a lean-calibrated production carb. Surging due to lower vacuum.
I would enlarge the idle feed tubes [ IFR ] by 0.002-3". As a starting point. There is nothing wrong with doing this.
Many people do not understand that this enlargement is not done to provide more idle fuel....it is done to provide more fuel for cruise..
There is ALWAYS enough fuel for idle. How do we know? Simple: the engine will stall if there is not enough fuel!
The idle cct also supplies the transfer slot fuel, where much of the cruising is done. That is why the IFRs are enlarged, not for idle fuel.
I would NOT trade timing for fuel. Reducing timing to fix a lean condition sacrifices power & economy & could cause o'heating.

 

[Orig69]

If it was me I would remove the metering rods to see if they are original and check the step up springs and pistons for freedom of movement, with pictures.