Plug fouling vs ignition voltage?

[Nut124]

Has anyone observed high ignition voltage resulting in more plug fouling?

I observed something like it today possibly.

Finally a nice day for a test drive of me new intake cam. Started the car up to let it warm up. Upon leaving, immediately noticed it was running on 3 of 4 cylinders, fouled plug?. Put it back in the garage. After dinner, went back to see which cyl was not firing. While idling at 3 cyls, pulled plug wires off the dizzy cap. As I pulled #4 off the cap, the engine picked up and started to run fine, as long as I kept the wire 1/2" or less from the cap where the spark could jump the gap. If I pushed the wire back into the cap, the engine would slow down, run on 3. If I kept a 3/8-1/2" cap, the engine would idle fine.

Almost seems like a higher ignition voltage will find ground in a fouled plug sooner than a lower voltage.

Should I get a lesser coil for less voltage? I do have trouble with plug fouling on occasion. The engine idled fine with almost a 1/2" visible gap at the dizzy.

[BOOT]

What coil? What ignition? What compression & plug gap?

Could be the weaker energy it was, then it couldn't jump/leak to were ever it was before firing the plug. If so then bad plug wires or plug maybe.

I'm not saying your wrong and I am no ignition expert. I do know some coils are better for higher RPM and there is a thing call coil tuning.

[hoodeng]

Not sure about your first statement. But what you have done by pulling the lead from the cap and introducing a bridgeable air gap is to have increased the discharge voltage for that plug, or until VR exceeds VA. The coil you have seems capable of providing the spark energy to make the engine run correctly in this instance.
A change of plugs is a cheap re test.
I have experienced plugs in engines that would run rough or misfire even though they looked relatively clean.

[Circlotron]

Nothing new there. 2-stroke lawn mower plugs have an internal gap for this exact purpose. Champion UJ18 for example.

viewtopic.php?t=45565

[rebelrouser]

as a technician if you told me your post, first thing I would do is hook up an ignition scope to see what the firing KV and burn time was on each cylinder. To keep a plug clean you need both to be right. One of the advantages of an MSD type ignition is that at low speeds the box will fire the plug three times making sure the mixture is fired, even if it is too rich. As engine speed increases the three pulses happen faster, making just one long hot spark. In pulling the plug off and making it jump further you increased the firing KV and reduced the burn time at the plug.

[Tom68]

Isn't the real question why the plug fouled in the first place ?

Sounds like a plug heat range issue or engine tune issue needs to be addressed unless you have some non conventional ignition system that you are questioning.

[Truckedup]

Isn't the real question why the plug fouled in the first place ?

Sounds like a plug heat range issue or engine tune issue needs to be addressed unless you have some non conventional ignition system that you are questioning.

Yes..and if its an electronic ignition it is recomended to short the plugs rather than pulling off wires

[Nut124]

Nothing new there. 2-stroke lawn mower plugs have an internal gap for this exact purpose. Champion UJ18 for example.

viewtopic.php?t=45565

I just thought it was an interesting finding.

The engine has big weber IDFs and it sometimes fouls plugs when idling. I almost feel like the #4 idle screw turns out on it's own. I used to run NGK6 but had put in one step colder for track use. May go back to 6 for street.

[chimpvalet]

Contact Keith Franck, proprietor of webstore at the attached link. He's done expert work analyzing and developing solutions for Webers' shortcomings.

https://www.webstore.com/user,pgr,82598 ... ther_items

Cheers