New Member - Carbon Fouled Spark Plugs

[Jpholland1978]

Hello all,

I am new to this forum and hoping to receive some guidance!

I purchased a 1965 Plymouth Satellite 383 with a Holley Carb and electronic ignition last year. The car was misfiring badly when I purchased it. For some time now, each of the spark plugs have become dry carbon fouled. I pull them out, clean them up, put them back in and the car runs for a couple of miles before cutting out and refusing to start. So I repeat the process and the car runs for a couple of miles again before cutting out and refusing to start again. I have repeated this process a number of times now with the same results, so clearly I am failing to deal with the underlying issue! I have tried to lean out the mixture which doesn’t appear to make any difference.

I am not yet particularly competent mechanically (!) and learning (or trying to) as I go along.

I wondered whether (a) anybody could recommend a mobile mechanic in the Kent area to look at this; and/or (b) whether anybody has any tips on how I can go about diagnosing / resolving the issue.

I’m sure I have left relevant details out but happy to provide more information if required.

Thanks in advance for your time and any help would be much appreciated.

James

[Pete]

Welcome to the Club and the Forum.

I guess I would start by checking the Carburettor Float bowl heights as it sounds (obviously) that it is over-fueling.

[Dave81]

Sounds to me like timing and the car is running overly rich (carbon deposits on plug end).
If its doing it in a couple of miles then it must be way off.

That would be my first port of call!!

[Charger]

hello there , welcome aboard

[Charger]

ignition ...
https://web.archive.org/web/20160214201 ... f=13&t=828

carb ...
https://web.archive.org/web/20160214202 ... =11&t=5308

loads on here about timing ...

http://www.moparuk.com/forums/viewtopic.php?t=45873

http://www.moparuk.com/forums/viewtopic.php?t=35148

http://www.moparuk.com/forums/viewtopic.php?t=35679

my recent timing exploits ...

http://www.moparuk.com/forums/viewtopic.php?t=46913

and some more of the same ...

http://www.moparuk.com/forums/viewtopic.php?t=46806

[Charger]

Modern fuel needs loads of initial advance otherwise half the fuel comes out the exhaust unburnt.

my 383 likes 20deg initial 34deg max all in at 2500rpm

[Jpholland1978]

Thank you for all the contributions so far! I shall be straight onto the suggestions at the weekend!

[Dave999]

if you have fouled up the plugs numerous times it may be worth getting a new set, gap them to standard before starting you quest for nice timing and carb settings

champion RJ12YC or NGK equivalent which is probably B?5?S or 6?S

gapped at something like 25 thou to 30 thou

dave

[Jpholland1978]

Thanks Dave. I have ordered new Champion plugs and a timing light so fingers crossed. Now I just have to prepare for the hours it takes to access and change the more difficult to reach spark plugs!

[Stu Twin]

if you have fouled up the plugs numerous times it may be worth getting a new set, gap them to standard before starting you quest for nice timing and carb settings

champion RJ12YC or NGK equivalent which is probably B?5?S or 6?S

gapped at something like 25 thou to 30 thou

dave

I've just fitted a new set of RJ12YC in the Plymouth (cause that's what it was supplied with)
And B6S in the Dodge.
And gapped them both to 35 thou.

Is that too much?
Both have a MSD Blaster coil.

[Dave999]

Probably not

i just err on the side of caution as too much isn't necessarily better it just heats up the coil and wears you ignition leads out quicker

you need just enough gap to avoid misfire in the RPM range (within reason don't go tiny gap that too will cause problems in the exact reverse of what i describe below)

altering the gap alters the timing i.e the bigger the gap the longer you wait for the spark

the bigger the gap the higher the Voltage of the spark but it is potentially sparking for a shorter period of time

is very high voltage and current for a short period of time better than medium voltage and longer current flow ?? dunno but it would certainly stress things less

spark power is current and voltage multiplied ..... and you need both..... although not strictly correct the voltage starts the spark and the current maintains it . starting it is harder than maintaining it and ultimately at higher RPM you are limited on how high the voltage can get due to the short dwell time.

current is limited by internal resistance of the coil and leads so with a coil designed to give more power a bigger gap is probably fine

basically a balancing act like most things, ball park middle and you are good to go

if it idles nice and runs great to the red line...all good

Dave

[Stu Twin]

Thanks Dave i can see the logic in (most) of that.
i might leave the gap as is for now & see how it goes. I noticed that some of the leads on the Dodge had started to get quite stiff and the outer insulation is breaking up. Been on there 10 years or so. So that probably isn't helping!

[Dave999]

yes

the outer case degrades due to heat and gets microscopic cracks. look at the running engine in the dark to see the arcing out through the cracks

and the inner core is a soft conductive rubbery substance it gets sliced and diced over the years by the massive voltage jolts and the resistance of the leads gets greater and greater. i.e the very thing that allows it to be a bendy conductor or a specific resistance to suppress radio noise (these days with no resistor in the plug cap) eventually becomes the leads downfall

old days with copper leads and a restor cap had some benefits. if you didn't flex them and they never corroded or got too hot and brittle you got longer service

Dave