Re: {Chrysler 300} 300F Backfire thoughts?

Use of Pertronix increases the odds greatly that the trouble lay with ignition and likely the Pertronix module itself. The older variety are known to eventually fail and backfiring is among the presentations.

-----Original Message-----
From: "Lindsey Fuller" <Lindsey@xxxxxxxxxxxxxxx>
Sent: Wednesday, July 31, 2024 3:47pm
To: "John Grady" <jkg@xxxxxxxxxxxxxxxxx>
Cc: "Dan Plotkin" <dplotkin@xxxxxxxxxxxxxxxxxxx>, "Carl Bilter" <cbilter@xxxxxxxxx>, "'Bob Meritt" <bob@xxxxxxxxxxxxx>, "Jean-Yves Chouinard" <jymopar@xxxxxxxxxxx>, "Jim Marino" <jpm0855@xxxxxxxxx>, "chrysler 300 club" <chrysler-300-club-international@xxxxxxxxxxxxxxxx>
Subject: Re: {Chrysler 300} 300F Backfire thoughts?

Thanks for all the input. I should have mentioned that I switched to Pertronics ignition during restoration 8 years ago. Not sure if that changes any of your ideas.

On Mon, Jul 29, 2024 at 8:10 AM John Grady <jkg@xxxxxxxxxxxxxxxxx> wrote:

very good point Dan , i jumped to tail pipe backfire , more likely a carb backfire , accell pump check valve sticks on these , no squirt ? one side . Especially off idle

Same issues apply . Haven’t be careful myself , which kind of backfire

I had quite a dance last week with one of my cars , will be long story , Later on . I write long stories . This one is real .

but end point : NEVER hold wire in hand to check spark or run with a coil wire off distributor or pulled plug wire etc . Unloaded plug volts can exceed 60000 will break down the coil inside , especially old one . voltage is clamped to 20000 or under , by the outside plug gap .Make tester of old plug and ground wire

All this last week led to discovering a 10$ tester on amazon with adjustable screw gap , set it to 20 kv , to test spark . Great tool . Never knew about it . Fits on wire . Critical in fact to check spark without hurting the coil inside . It will hold the bolts down like a plug

Once you hurt your coil you get occasional poor running , or one day won’t start right , on and on and sends you down a very long garden path maybe for years .And intermittent as all get out . Reason : Part of spark is sometimes reduced by coil carbon track inside the coil . Sometimes …

I have done that we all have . It DOES damage coil .

We keep

learning

John

Begin forwarded message:

From: John Grady <jkg@xxxxxxxxxxxxxxxxx>
Date: July 29, 2024 at 8:03:08 AM EDT
To: Lindsey <lindsey@xxxxxxxxxxxxxxx>
Subject: Re: {Chrysler 300} 300F Backfire thoughts?

hi backfire is not usually a plug issue or wire at plug either . A failure there usually means obvious skip ,( it is then not firing, as opposed to firing ant wrong time) and although that skip could lead to fuel vapor in exhaust etc , i have never seen that . And it would skip . If skip , dirty plug a hard run might help , like uphill .

but my money is on incorrect points setting too tight . you really can’t do it right with out an old fashioned dwell meter as they are critical and tend to change as you tighten the screw . See ebay old sears dwell meter

Also the capacitor . If someone replaced yours with one with rubber conical nose they are junk . Hard to find but original mopar has a copper strap out of cap
I may not be right on all this , from afar but what I would do …
hope it helps
j

On Jul 28, 2024, at 10:24 PM, Lindsey <lindsey@xxxxxxxxxxxxxxx> wrote:

Have hardly driven my F this year due to wet and nasty weather and waiting to get my brakes fixed properly. Finally took it for an hour or so city cruise last Sunday. After a slow crawl through a show and shine, i stopped at a red light. Accelerated medium throttle and heard a backfire, probably mine. 5 minutes later hit another red light and motor was shaking at idle. Obviously a cylinder not happy. Got home ok. Not able to bend down at moment to pull front wheels and access covers to get at plugs. No signs of arching on coil or distributor cap contacts that i could see. Cap for #1 cylinder had a bit of loose black stuff at bottom which cleaned up with a q tip. Took it out again and seemed fine, motor smooth, good moderate acceleration, no highway. Came to a stop sign on a remote road. Didn’t come to a full stop, then began accelerating modestly and a small backfire. The car has always run a bit rich since restoration i believe. Any thoughts before I get it to my out of town mechanic?

Thanks.

Lindsey in fires fire free Winnipeg

Sent from my iPad

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