Sparking plugs

[BDA]

I've been running 7 heat range NGK plugs and the engine seemed to run pretty well. Not perfect but it idled pretty smoothly at 1000 rpm, accelerated pretty well, (though it occasionally stumbled a little from a stop but not much), and ran smoothly up to 6000.

Then I let it idle for about 15 - 20 minutes while I talked to my neighbor. I finished talking and drove into the garage. The next morning, I went to take it out and it was soon pretty obvious that I had some fouled plugs so I drove for quite a while at elevated rpm (4000 - 5000). This used to clear it out when I used to run colder plugs but it didn't clear up this time. I took a look at the plugs and the front two were the ones that fouled so it's pretty clear to me that I have some work to do on that carb, but in the meantime I'm looking at buying warmer plugs. (Or should I try to clean them?) I found some 6 heat range plugs but the hex is 5/8 rather than 13/16. Is there any reason why I shouldn't use the smaller hex plugs (Seems like it shouldn't matter but just making sure).

[Pfreen]

I recently installed ngk iridium plugs bpr7eix.  They fouled very quickly.  I now use champion n7y plugs and don’ have a problem with fouling.  They are a lot cheaper as well.

[jbcollier]

One man's plug is another man's poison.

There are a lot of counterfeit NGK spark plugs out there.  Make sure you buy from a reputable supplier.

Fuel formulations vary from location to location so different issues can arise.  Tune your carbs with a air/fuel gauge matched to a wide-band O2 sensor.  The odd fuels we run these days do not colour plugs the same way as they used to.  Then use the heat range recommended and go up or down no more than one heat range if needed.

Got a wild cam?  Run it hard?  Then you will have to run colder plugs and watch you don't idle it too long.  Ask any Lamborghini Miura owner, they know the drill.

[Certified Lotus]

Never let your engine idle too long! I use NGK BP6ES plugs in my Weber carb twin Cam Engines. I used to use Bosch RO 102, but they are only good for constant high rpm use. They foul way too quickly for street use.

[BDA]

Thanks guys! Ordered warmer plugs, will play with the carbs when I get them and watch the idling.

[Roger]

I find NGK 7s just a bit too hard, both in Elan and Europa TC.
6s are just right. Road use only, mind you.

[BDA]

Thanks, Roger. I have 6s on their way.

[buzzer]

Ngk bp6es are the plugs to use in my opinion for normal use and for tune up to 150 bhp. For hard use I’d go hotter or more specialised.

[jbcollier]

Hard use = more full throttle = more heat = a colder plug.

[buzzer]

Running 2 stroke motorbikes was the learning curve to me in my younger days on plugs.
Running around town and they’d foul up. A good thrash and they’d misfire. Always had sets of different heat ranges from 6 to 9... and nothing other than ngk

[BDA]

jb - Yeah, I don't track or even autocross my car. As I said, I had been running 8s with minor issues. I had a panic stop and the plugs got fuel fouled. The moderator at sidedraft central suggested going one or two ranges warmer. I ran 7s with no known issues till I had the problem I mentioned above. When I get my 6s, I'll look at the carbs and will surely end up leaning out the front carb and might enrich the rear - the 3 & 4 plug were nice and clean with a hint of brown color on the insulator.

buzzer - I can imagine a 2 cycle bike would make plug selection a challenge.

[EuropatcSPECIAL]

I have to agree 7's have always been problematic, since I changed to  NGK BP6ES in both the Elan and Europa I've had no more problems

[surfguitar58]

Oy, this is all news to me. I thought sparkplugs were sparkplugs. Guess I have some reading to do.

Question: I am going to be installing electronic ignition with a Pertronix "Flamethrower" coil. Would a high power coil affect my choice in sparkplugs?

What about the type of fuel used wrt sparkplug choices? (A pilot friend offered to hook me up with some avgas, but I imagine I'll be stuck with pump-premium at some point.)

Sounds like the consensus is NGK 6, barring extenuating circumstances. Every day a new lesson.

Tom

[Certified Lotus]

I’ve got electronic ignition in my cars. Don’t use av gas. Your better off tuning for high octane pump gas (93 if available). Unless your racing only (auto cross does not count as racing) no sense in using av gas. (I’m sure I’ll get rained on for this comment. Fair warning I’m an ex-track guy with lots of experience with fuel mixtures and blown engines).

“AvGas is short for Aviation Gasoline. AvGas is of interest to motoring enthusiasts because of its availability, octane rating and low price compared to commercial race fuels. AvGas might seem an obvious choice but closer study raises some doubt.

AvGas LL100 stands for "Low Lead 100 Octane". TEL (Tetra-ethyl-lead) is added to raise the octane. When used in a motor vehicle this fuel will leave a lot of lead deposits in the motor. 100LL has a high lead content (0.5 grams per litre), even higher than leaded race fuels. The deposits left when TEL(lead) is burned are corrosive and damaging to valves, valve guides, valve seats and cylinder heads. Lead deposits will also block oxygen(lambda) sensors and catalytic converters and foul spark plugs even after only a short use. Also, 100LL has a chemical package added to make it perform at high altitude, and that isn't the best thing for motor vehicle performance here on the ground.

AvGas is blended for large-bore, long-stroke, low RPM engines which run at high altitude. While AvGas' higher octane is useful, smaller-bore, shorter-stroke, high RPM engines will perform better on racing fuel or high quality octane boosters. AvGas has lower volatility so when used in proportions higher than about 40%, part-throttle drivability and cold starts may be compromised. AvGas has a lower specific gravity so it will require a change in air-fuel ratio calibration for the engine to perform at its best. LL100 is blended with a high percentage of aromatics causing reduced throttle response which is not an issue with an aircraft engine but certainly an issue in a high-performance automotive engine. These high levels of aromatics will also damage rubber components in automotive fuel systems such as fuel lines, fuel pump seals and injector washers.”

[BDA]

The temperature range of the plug is a rating of how quickly it conducts heat from the plug to the water jacket. If the electrodes get too hot - or rather if the heat isn't conducted quickly enough, the hot electrode can ignite the fuel-air mixture causing pre-ignition. As JB said, if you run hard - high rpms - you'd want a cooler plug because there is less time to dissipate the heat. On the other hand, the plug has to retain a certain amount of heat to burn away oil or excess fuel so if you don't run your motor hard and your plugs are too cool, you'll get fouling like I did. All this is with the engine in otherwise good tune.

It seems that if you're using NGK, you'd probably want the 6 heat range like the rest of us. The ignition system shouldn't matter. BTW - I have a Petronix setup in my car, too. They're great!