I have a customers car that could really use an engine
rebuild but for now he is happy with it. After about 100
miles they start to miss a little. I have bead blasted them
out and every thing is smooth again for a while. I am using
Champion RN12YC. Is there another plug that might last a
little longer before cleaning?
Thanks
Wes Keyes
York, Maine–
Wes Keyes
York Maine, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from Weston Keyes sent Mon 27 Jun 2011:
Wes
You must first determine the cause of your plug fouling. If
it is fuel, you can lean it out a bit, if oil is fouling the
plugs, try a supplement to reduce oil burning. A hotter plug
will last a little longer between cleaning, but until the
cause is rectified, the problem will return. Try a Champion
RN14YC.
Joel–
ex jag, '66 E-type S1 4.2, '56 XK140dhc, '97 XJ-6
Denison, TX, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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In reply to a message from Weston Keyes sent Mon 27 Jun 2011:
Wes,
Try NGK BPR5ES.
Paul–
The original message included these comments:
Hello Folks,
I have a customers car that could really use an engine
rebuild but for now he is happy with it. After about 100
miles they start to miss a little. I have bead blasted them
out and every thing is smooth again for a while. I am using
Champion RN12YC. Is there another plug that might last a
little longer before cleaning?
Wes Keyes
York, Maine
Wes;
Try the correct N5C Champions… (sparkplugs.com) The
“R” resistor plugs reduce the power of the coil gointg to the
plugs, as do “Resistor (aka Carbon) wires”…
Makes NO sense, at all, to “choke down” what little power
comes from the coil… The XK needs all the “fire” it can get!
Not to mention the “12” is NOT the correct heat-range for
an XK (assuming you are still working on the 120)… The
N12YC, if I am not mistaken, is an XJ-6 spark plug…
All the above assumes that the engine is NOT burning
so much oil as to be “oil fouling” the plugs, as opposed
to “fuel rich” fouling… If the former, NOTHING is
going to help… If the latter, adjust the carbs correctly!
Charles #677556.----- Original Message -----
From: “Weston Keyes”
Hello Folks,
I have a customers car that could really use an engine
rebuild but for now he is happy with it. After about 100
miles they start to miss a little. I have bead blasted them
out and every thing is smooth again for a while. I am using
Champion RN12YC. Is there another plug that might last a
little longer before cleaning?
Wes, Paul and Charles are correct about the causes and fixes for the
fouling. I’ve had good results with the NGK BKR5ES plugs gapped to 0.025 for
the early XKs.
Bob Grossman
In reply to a message from Weston Keyes sent Mon 27 Jun 2011:
Wes,
You could order a new dizzy and flamethrower coil; which I
swear by in several of my Jaguars. They in unison, put out a
lot of power to the plugs and both can be retained once the
customer rebuilds their engine. Bob G helped me get these in
top order and reliablity is perfect.
Hi Bob, l know it was years ago but, what made you use 0.25 plug gap instead of the NGK SETTING OF 0.35 ? I’m fairly new to being an XK 120 owner, mine has a 140 or mk2 engine and I’m having the fouling problem. Just bought a set of NGK BP5ES to replace BP6ES so thought I’d ask before fitting.
Hello Guys : Im Australia this post is May 2022 , I find 98 octane fuel blacks the plugs quite quickly compared to 95 octane. Also depending if you have a Manuel chock , try and use it for the least amount of time once the engine fires. I mainly talking about carburetor engines. The smaller plug gaps ans other options may have come about over time again due to modern fuels . Kind regards Michael
I’m going to say that you need to have your carburetors set more accurately: they really should not be that large a difference between different octanes of fuel.
Thank You Paul , and I dare say you are correct , however I have seen the 98 not as clean as the 95 on other types of engines also . Again this could be that they need better tuning. I have also felt the spark quality could be improved on my series 2 , and that again would probably help . Great forum .
Maybe the 95 contains ethanol and runs leaner? Or it detonates any deposits right off, if you don’t need 98 stay with the 95 and if you do have pinking you need to use 98 and adjust your mixture accordingly. 98 and 95 shouldn’t burn that differently. The more ethanol the leaner it gets as there’s less energy in it, modern cars can adjust for it but ours can’t.
Great response David , There clearly is a difference between 95 vrs 98 and the deposits , that being said a better stronger spark or spark plug type may eliminate this .