C1 Fouled spark plug

[Nicholas L.]

Replaced spark plugs and one was fouled. Passenger side closest to radiator. Original engine with two WCFB carbs. 270HP. MSD electronic ignition. Drove 50 miles on Sunday and same plug fouled again. Any suggestions. Thanks in advance.

[Leif A.]

Re: C1 Fouled spark plug

How many miles on the engine since valve seals last replaced? Even if fairly recently, there could still be a faulty/bad valve seal.

[Nicholas L.]

Re: C1 Fouled spark plug

It has been 30 years since engine rebuild. Valve seal replacement is an excellent suggestions. Thanks.

[Dan H.]

Re: C1 Fouled spark plug

Take an ohm meter and read resistance in plug wire. Happy hunting, Dan

[Nicholas L.]

Re: C1 Fouled spark plug

Thanks. Will check resistance tomorrow.

[Tim S.]

Re: C1 Fouled spark plug

Have you checked the torque on the intake manifold?

[Duke W.]

Re: C1 Fouled spark plug

What's the manufacturer and number of the installed plugs? Is the heat range equivalent to AC "5"? Are you detecting any misfiring?

Is the "fouling" black and wet looking like what would be expected if excess oil is getting into the combustion chamber or black and dry, which could indicate an overly rich mixture? A photo would help.

As asked in post #2 how many actual miles are one the engine, and are you certain that the valve seals have never been replaced or the heads removed for a refresh?

Duke

[Nicholas L.]

Re: C1 Fouled spark plug

Delco R53. Plug is black and dry. Driven 20,000 in last 30 years. Previous owner said he rebuilt engine prior to selling. 82,000 total miles. No engine work since I owned it.
correction on plug. It is R45S.

[Duke W.]

Re: C1 Fouled spark plug

I don't know what a Delco R53 plug is other than it's a resistor type. Do you mean R43? If so that plug is two heat ranges below what a street driven early small block should use.

The second digit in the traditional AC numbering system is the heat range and the higher the number the hotter the plug. The semi-correct AC plug would be the R45. I say "semi-correct because the OE plugs were non-resistor type. Since all Corvette engines are powerful for the weight of the car, the engines operate at low average load, and in sane public road driving you can't keep them highly loaded for more than a few seconds at a time.

Therefore, they need a "hot" plug to burn off deposits, but not too hot to cause the plug to be a pre-ignition source, which can lead to destructive detonation.

The "4" means 14mm thread, 3/8" reach, gasket seat, 13/16" hex.

The OE plug was AC 44. GM quit manufacturing spark plugs decades ago. ( I have no idea who manufacturers AC-Delco plugs nowadays.) And despite building millions of small blocks with AC 44 plug as OE s they quit offering heat range 4 in addition to discontinuing non-resistor plugs. What morons let that happen? Never mind... it's a rhetorical question.

Despite the AC 44 being too cold for normal road use instead of replacing it in the catalogs with the R45, they chose the R43, which is WAAAAY to cold. Back in the sixties I installed a set of AC 43s when I spent a day hot lapping the 2.25 mile Kent road racing course with my 340 HP SWC. Hot lapping a big track means sustained high load for most of the lap, so a "cold" plug is needed, And AC heat range 3 was just right for that kind of sustained high output service.

I bet you went to an auto parts store, and the kid asked you the make, model, and engine type. He looks at his computer and it says R43. It happens to a lot of guys and a different brand catalog will also call out a too cold plug because they cross reference to the incorrect GM callout from over 30 years ago.

Don't feel bad. This happens to a lot of guys and with many more parts than just spark plugs

The ONLY REASON to use AC plugs is if you are campaigning your Corvette in NCRS judging. If not, first choice is Denso W14-U and second choice is NGK B4. Both are non-resistor "two dollar "copper core spark plugs equivalent to the long-out of production AC 45. Well, due to Bidenflation they're now about three bucks each.

With proper ignition and fuel system performance they should last at least 15,000 miles and 30,000 if both are really dialed in and stay that way for the duration.



Next... since the black fouling is dry it's probably not oil fouling. If all or most were so-fouled I would suspect and overly rich mixture that is a common problem with the 2 x 4 carb system, which are set up rich due to serious mixture distribution issues. (There's a reason Chevrolet abandoned 2 x 4 carb setups after the last 409 in '64.)

So, IMO the first thing you should do is look at the ignition system particularly the #2 plug wire. I don't know what MSD system you have, but what about the wires? Are they OE type RFI suppression wires or something else. The OE type RFI suppression wires should be no more than about 5000 ohms per foot. and 1, 3, 2, and 4 are about three feet long.

Measure resistance of all eight and report. You could also swap #2 and 4 wires at both the plugs and cap and then if #4 fouls it's a pretty good indictment against that wire.

The only way to solve your problem, like any other problem is to test, gather data, and go from there.

Follow the science, right, like the political hacks say, but science is based on data and without data you have no science! Of course you can just start looking at anything and everything suggested... just try everything and hope one is right, but that is time consuming and can often lead you into a black hole. It's like rearranging deck chairs on the Titanic in various ways, but that won't change the final outcome!

If you only buy parts occasionally like for a tune-up or minor repair it's a good idea to check here first. Both the GM parts catalogs and aftermarket catalogs have plenty of errors that can lead you astray. Never rely solely on a part counter guy looking at the computer.

Duke

[Nicholas L.]

Re: C1 Fouled spark plug

Thanks for the thorough explanation.

[Nicholas L.]

Re: C1 Fouled spark plug

Correction on plug. It is R45S. Poor typing skills.

[Mark E.]

Re: C1 Fouled spark plug

The ONLY REASON to use AC plugs is if you are campaigning your Corvette in NCRS judging. If not, first choice is Denso W14-U and second choice is NGK B4.
Duke

Duke,

Why do you recommend Denso and NGK?

[Duke W.]

Re: C1 Fouled spark plug

Two reasons. First, they are non-resistor like OE plugs (up to 1968). The point ignitions are marginal on ignition energy reserve (available per spark energy is about half the TI and HEI), and resistor plugs lower it even more because the resistors dissipate energy as heat. Beginning in the '69 model year GM switched to resistor plugs due to FCC RFI interference requirements, and the AC brand hasn't offered non-resistor plugs for decades.

Second Denso and NGK are high quality spark plug manufacturers. I have no idea who actually manufacturers AC spark plugs... probably the lowest bidder. GM has not manufactured spark plugs (or most electrical parts) since the nineties. "AC Delco" is just a marketing outfit.

Back in the sixties I found that the OE AC 44 plugs were too cold for my SWC's 340 HP engine in normal driving and were constantly fouling. The AC 45 plug pretty much eliminated this issue. I installed AC 43 plugs for a day's hot-lapping at Kent. (I believe it's now called Pacific Raceways, about 20 miles south of downtown Seattle near the town of Kent, Washington.)

The Denso W14-U and NGK B4 (both non-resistor) cross reference from the long out-of-production AC 45 in their respective catalogs.

I've been recommending them for at least 20 years and have never heard any unfavorable reports from those who followed my advice.

I prefer the Denso W14-U due to its "U-groove" ground electrode. Sparks like to propagate from edges like corners. Look at any well worn plug and you will see the electrode corners are rounded off. The U-groove provides additional corners for spark propagation.

NGKs common line of copper core plugs (V-Power) feature a V-groove in the center electrode, which accomplishes the same goal as Denso's U-groove, however, the B4 is an older design that was never upgraded to the V-Power type.

Duke

[Mark E.]

Re: C1 Fouled spark plug

Interesting. Thanks Duke.

[David M.]

Re: C1 Fouled spark plug

Fuel or oil fouling?
Swap the fouled plug with a good one from another cylinder. Do the same with the wire. See if the foul follows the plug or wire.