Magnetic Impulse Ignition System

[croderique]

Hello, I recently purchased a 1964 Chrysler 300 convertible w/ 383 cuin and Pushbutton Auto from the estate of a Chrysler dealer mechanic who bought it new. (My first Chrysler, I normally have Chevys). It only has 74,000 miles. I’m trying to figure out what modifications he made. One was the addition of a Magnetic Impulse Ignition System. When I check the timing without vacuum it was way off. I set it to 10 degrees BTC as shown in the shop manual without the vacuum hooked up. It idles at 500 rpm without the vacuum but only pulls 12 in of vacuum and the needle bounces between 10 and 14in. The dwell angle is about 40 degrees.

Then when I hook up the vacuum to the distributor the timing jumps to about 18-20 degrees, at idle, as far as I can tell. When I hook up the distributor vacuum it idles at 1,000 rpm with 17in of steady vacuum but it has 18-20 degrees of advance. I can’t get it to idle at less rpm.

I have a paper instruction that came with the car, and it shows no advance until 1,200 rpm and maxes out at 18-20 degrees at about 1,800 rpm. Mine starts at 18-20 degrees and maxes out way above that by 1,800 rpm.

I believe the Magnetic Impulse Ignition System was why he set the timing to 10 degrees with vacuum advance hooked up. Any help would be appreciated.
Thanks
Chuck

 

[Davea Lux]

It sounds like the vacuum advance is hooked to the wrong port and is drawing manifold vacuum. If you do not have one already, down load the Mopar service manual for free at www.mymopar.com. Manuals are in the tools/reference section. There should be a ported vacuum connection at the base of the carb. This port will have little or no vacuum at idle and the vacuum will pick up as the throttle is opened up, this is what is supposed to activate the vacuum advance. It would help to know which distributor and ignition you are running. In the early 70's the factory offered an electronic conversion, but there were also several after market systems available including a true magneto system.

Dave

 

[croderique]

Thanks. Yes I have the shop manual. The vacuum port for the distributor comes from the only port available on a Carter AFB. The Magnetic Impulse Ignition System is a Chrysler branded P3960256.

 

[1970FuryConv]

Hello, I recently purchased a 1964 Chrysler 300 convertible w/ 383 cuin and Pushbutton Auto from the estate of a Chrysler dealer mechanic who bought it new. (My first Chrysler, I normally have Chevys). It only has 74,000 miles. I’m trying to figure out what modifications he made. One was the addition of a Magnetic Impulse Ignition System. When I check the timing without vacuum it was way off. I set it to 10 degrees BTC as shown in the shop manual without the vacuum hooked up. It idles at 500 rpm without the vacuum but only pulls 12 in of vacuum and the needle bounces between 10 and 14in. The dwell angle is about 40 degrees.

Then when I hook up the vacuum to the distributor the timing jumps to about 18-20 degrees, at idle, as far as I can tell. When I hook up the distributor vacuum it idles at 1,000 rpm with 17in of steady vacuum but it has 18-20 degrees of advance. I can’t get it to idle at less rpm.

I have a paper instruction that came with the car, and it shows no advance until 1,200 rpm and maxes out at 18-20 degrees at about 1,800 rpm. Mine starts at 18-20 degrees and maxes out way above that by 1,800 rpm.

I believe the Magnetic Impulse Ignition System was why he set the timing to 10 degrees with vacuum advance hooked up. Any help would be appreciated.
Thanks
Chuck

Congrats on your purchase! 74K convertible, push button big block!

Where are you connecting the vacuum meter hose?

If the car is running at idle, does the distributor advance vacuum port have vacuum? It should not. Connecting the vacuum advance hose to a Chrysler engine should not do what you describe. If you are measuring that much vacuum at the distributor vacuum advance port at idle, either it's the wrong advance port or the deceased previous owner altered the carb.

Dwell is a concern. Should be 28-33°.

Vacuum needle bouncing is also a concern. If no vacuum leaks, it should be rock steady. Usually, if not, it indicates a valve train problem. At least it is steady at when vacuum advance is connected.

Rick Ehrenberg sells electronic ignition conversion packages on ebay. Good quality. He is also excellent at answering questions. Maybe ditch magnetic impulse in favor of something new.

 

[CBODY67]

As with the OEM Chrysler electronic ignition system, "dwell" might not match what it would be if it had ignition points. Which gets into just which electronic ignition system is on the engine. IF the distributor has points in it, then adjust the point gap and do not worry about the dwell reading. Although 40 degrees of dwell sounds more like a factory dual-point distributor dwell reading.

Obviously, the advance curve is a bit quicker than stock, BUT the type of ignition system usually has no bearing upon where the base timing is set. Looking at factory distributor advance specs, it is not unual for the mechanical advance to start just over 1000 engine rpm.

Do make sure the vac line for the vac advance is hooked to a ported vacuum source rather than a full-manifold vac source. The vac line for the choke pull-off diaphram would be hooked to full-mainfold vacuum, but the distributror vac advance port should be "ported" (with little to no vac at hot base idle). It usually takes about 9" Hg for the vac advance to start working.

Seems like that early Chrylsler electronic ign system was a "capacitance discharge" type of system? Made by Prestolite, as I recall.

Does the number on the carb match what the service manual indicates?

Just some thoughts,
CBODY67

 

[croderique]

I got the brake booster rebuilt and finally got the car running good. It now has the fuel tank cleaned, new hoses, new fuel filters and the AFB refurbished. Idles a little high aa the choke doesn't open fully. I will work on that. However, at cruising, say 40mph, if you stomp on the gas it downshifts, takes off then immediately falls on its face. You let off the gas and it goes back to cruising normally. I suspect the Chrysler electronic ignition. I saw a YouTube video that said you can use a NAPA control module in place of the Chrysler one. Anyone have any experience with this issue and/or NAPA module?
Thanks, Chuck

 

[Big_John]

I got the brake booster rebuilt and finally got the car running good. It now has the fuel tank cleaned, new hoses, new fuel filters and the AFB refurbished. Idles a little high aa the choke doesn't open fully. I will work on that. However, at cruising, say 40mph, if you stomp on the gas it downshifts, takes off then immediately falls on its face. You let off the gas and it goes back to cruising normally. I suspect the Chrysler electronic ignition. I saw a YouTube video that said you can use a NAPA control module in place of the Chrysler one. Anyone have any experience with this issue and/or NAPA module?
Thanks, Chuck

The ECM won't cause that issue. They pretty much work or they don't work.

With the choke not opening completely, the secondaries are limited from opening by the choke linkage. This may or may not be the problem.

 

[CBODY67]

Adjust the choke thermostat such that the choke just barely closes by itself at 70 degrees F amgient (engine, carb, surrounding air). Then retry the "WOT 3-1 downshift" sequence again. Might need to readjust 1-2 marks leaner on the gauge. The thermostatic sspring will tighten with age, so some "lean tweaks" will put things back "right" again, from my experiences.

 

[thrashingcows]

Sounds more like a carb issue....I have messed around with OEM AVS and AFB carbs, different jets, meetering rods, springs and could never get a stock one to perform well. I had one motor that I eventually just bought a 750 Edelbrock with vacuum secondaries and that sure woke the motor up, had performance off the line and all the way through to when I decided to lift my foot.