Electronic ignition "kit" distributor question-vacuum advance

[challenger]

I am still chasing my tail with the Edelbrock 1411 carburetor on my 1970 300 vert.
The issues I have are a very slight stumble from a stop and while cruising and letting off & getting back on the throttle and a detonation at light throtlle while cruising. I completely disassembled the carburetor again and cleaned it. There was a tiny bit of material in the idle tubes which I took care of. This seems to have helped. The stumble is very slight and the detonation occurs at a very specific throttle position at highway speed.
I have the largest primary jet .113 and the smallest metering rod installed as well as the strongest step-up spring.
I tried lowering the initial timing to 5* BTDC from 12* and this has no effect at all on the detonation although it does make the car slower from a stop.
I thought my distributor was a Mopar Performance unit but it is not and I cannot see any way to adjust the vacuum advance.
I'd like to see if limiting the vacuum advance threshold would have an effect on the detonation. The stumble is something I can live with but the detonation is right at cruising/highway speed and is going to ruin the motor I fear.
I know there are no vacuum leaks that would cause a lean condition.
I feel it is down to vacuum advance timing OR the 1411 is running partially off the idle/transition/cruise circuit and is still too lean. I've been trying to talk with Edelbrock but cannot get through to see if possibly opening up the idle tube or changing something else might give me driveability.
As a strange idea-I have the original Carter off this car and the metering rods are identical in shape & length but the carter rods, according to the FSM, have three steps. The rods are a good bit smaller in diameter however. I'm wondering if anyone has tried these in an Edelbrock AFB/1411?
Thanks
Howard

 

[70bigblockdodge]

Re. Your distrinutor as long as it is a Chrysler dist. And not a prestolite(with a hex head on nipple end of vacuum adv canister put a 3/32 Allen wrench in nipple hole it my take some poking but its in there turn ccw it will pull it off quicker as you step onto throttle at cruise to pick up road speed.

 

[saylor]

can you put the other carb on and see if the problem goes away? maybe eliminate the carb vs. the timing

 

[Fratzog]

Howard I'm going through similar issues with the 1411 on my 68 Monaco 500 w/440. In my case it's intermittant ping at medium throttle and a lot more at WOT. There's occasional stumble pulling out of low speed turns. Motor is a recent rebuild with a mild cam. I don't know about the idle/transition/cruise circuit. The initial timing has also been reduced to 5* from the 8* where it started. The vacuum can on the distributor has been turned off so its a non issue. Mine is adjusted by inserting an allen key into the vacuum can where the hose connects. I've also gone as rich as the owners manual allows on needles and the primary/2ndry jets. I've also gone to cold racing plugs. Frankly I'm no further ahead. The 440 is a 77 block that came with a 850 Thermoquad that needed a rebuild. Maybe I'll try that if nothing else works. I hope you don't mind my piggy backing on this thread. Fred

 

[thrashingcows]

What is the specs on your motor and Cam...a lot of this could be timing and distributor related.

 

[challenger]

It is a stock 440 TNT original to the car with 55k miles on it.
I suppose I have a Prestolite distributor because the vacuum advance can has a hex shape. I would swear it came as part of the Mopar EI kit with the orange box?
Thanks
Howard

 

[challenger]

I did some more investigating, trial & error.
I've been trying to use an Allen wrench with a ball shape end. I've generally found these to be just slightly smaller than regular but in this case it was larger. On a whim I tried another 3/32" Allen wrench & it fit the vacuum can. I turned it CCW 2 turns and took a ride. It seemed like the light throttle detonation was a little less but I couldn't be sure. I pulled over & took off the vacuum advance from the carburetor (doesn't everyone have a carburetor nipple plug in their pocket?) The detonation went away so I assume there is just too much timing at light throttle. I took the cap off the distributor and it has a 9* mark on the arm for 18* vacuum advance at high manifold vacuum.
I imagine the most vacuum advance I can have while cruising without detonation would be the most economical yes? I also found that I have the Mallory distributor with the adjustable mechanical advance which I am very pleased about. I will dial out about 5* total mechanical advance and see if I get rid of the light throttle detonation while I have the vacuum advance hooked up.
I've not checked this accurately because the timing tape I have only goes to 40* but what is a recommended "all in" timing for this heavy car? I know this is just one number to consider but while addressing the light throttle ping it is the number that will be best to get right.
I can worry about the initial & mechanical total without the vacuum advance once I get the ping out at light throttle.
I hate to ask this but could this still not be a pinging from a lean condition in the carburetor?
Thanks
Howard

 

[Fratzog]

I hate to ask this but could this still not be a pinging from a lean condition in the carburetor?
Thanks
Howard

If you have already gone as large as possible on your jets and the smallest needles how else do you richen the carb

 

[challenger]

If you have already gone as large as possible on your jets and the smallest needles how else do you richen the carb

I don't know other than drilling the idle tubes? I was hoping someone else may have the same model carburetor & could offer their experience. I am trying to understand the timing/carburetor indications regarding this detonation & so far the timing is the only thing that has gotten rid of it. Still it may not be the answer or so I am thinking?
Thanks
Howard

 

[Fratzog]

I think our problems are distinguishable in that I have the pinging when the 440 is warm, mostly at WOT and only periodicly at part throttle. I will continue to monitor this thread in the hope that someone with knowledge and experience can point us in the right direction.

 

[thrashingcows]

Sure sounds like it's timing after your last couple responses. Think you want to see about 32-38 total advance....that is static timing at the crank, mechanical advance in the dizzy, and vacuum advance. I like to set around 10-12 at the crank, then check to see what I have as mechanical in the dizzy, and when it starts to come in. Then I will play with the vacuum advance.

You really need to pick up a digital dial back timing light....it makes working on your ignition system so much easier. You can check each component in the ignition system easily by dialing back the timing mark on the crank back to zero and then looking at how many degrees you have on the digital timing light. You can also see at what RPM your mechanical advance starts to come it, and by what RPM it is all in.

 

[commando1]

You really need to pick up a digital dial back timing light....it makes working on your ignition system so much easier.

I thought I would give one of those new-fangled lights a try a few years ago. Couldn't figure it out. Gave it away and went back to Ol Reliable. LOL
Pull trigger.
Light strobes.
Watch line dance back and forth.
Watch dancing line move up and down while twisting distributor.

 

[1978 NYB]

I have a Craftsman Timing Analyzer that I've had for at least 20 years and works great. Adjustable from 0 to 65 degrees.

 

[Fratzog]

I think Howard stated that his timing tape went to 40* so he shouldn't really need one of those lights?