Ngk Spark Plugs

[type26owner]

My BP6Es presently don't completely self-clean themselves. I've got a dark brown stripe across the insulator from the electrode to the housing directly under the ground tag but the rest of the insulator appears to be like the perfect heat range depicted at the www.ngksparkplugs.com tech info section. Also when coasting in gear down a grade for at least 30 seconds the plugs foul enough from overcooling I assume so at the bottom it will idle okay but hesitates to accelerate on the first blip of the throttle. Runs perfectly after the first blip and the plugs cleanup (?). I have zero oil consumption, the Webers are tuned to perfection, the ignition is perfect and the compression is 190 to 180 psi on a completely stock engine. Is running the next hotter plug (BP5ES) okay in the twincam? Anyone have first hand experience on this subject?
TIA
Keith

[rgh0]

Keith

I would not be afraid to experiement as plug needs are very sensitive to driving usage syle and fuel variation, even fuel from a single refinery varies from day to day depending on the feedstocks run and how they blended it up to comply with the fuel specification. I use BP6ES in my roagoing plus 2 which has a stock standard big valve engine but they can foul up if I use them in heavy traffic for extended periods ( eg daily commuting for several weeks) without a chance for higher speed cruising to clean them up.

If I tried hotter BP5ES I would check them very regularily for overheating and listen carefully for preignition until I was confident they were not too hot.

If you really want to experiment you can play with some of the fancier plug types with multiple electrodes and exotic metals and shapes to the electrodes that are around these days. You may find one of these more tolerant of the consitions in your car than the traditional designs.

Rohan

[type26owner]

Hi Rohan,
Tuning the twincam with Webers to run well using California's Reformulated Fuel is tricky. It's soon going to be nearly impossible I'm hearing rumblings now. Supposedly the NEW Reformulated Fuel due to be introduced within two years won't work in MOST carburetors. Conspiracy theory, that's how the older cars are to be removed from the road since they don't rust away here. I'm in process of installing a vintage fuel injection system.

I'm definitely going to try the hotter plugs and heed your advice monitoring them. The more expensive plugs usually offer no added value versus the cost IMO.
Thanks,
Keith

[type26owner]

A friend suggested I coast down the same steep grade with it out of gear but riding the brakes all the way and observe what happens. Did that procedure this morning and to my dismay I found the engine idles for about two seconds and dies. Repeated the experiment and it consistantly dies. It idles nearly perfectly when back on flat ground. Anyone else ever have this problem?

Clearly the plugs overcooling and causing this condition has a probability factor of about zero. I'm suspecting it's an issue instead with the fuel level in the Weber float bowls and it floods the engine into dying. This is bizarre!
Keith

[rgh0]

Hi Keith

The reformulated fuels are being made "heavier" with less low molecular weight components. The dont evaporate as easily and thus dont cause as many air emission problems. In fuel injection vaporisation is less critical than in most carburettor cars as the fuel is sprayed under high pressure into the inlet valve area so you get a decent fuel air mix even when the engine is cold. In most carb cars the fuels puddles in the inlet rack and does not vaporise in similar conditions.

The good news for Lotus Weber engine drivers is that the one thoat per port and resultant strong pulse sucking the fuel and the straight inlet pipes result in fuel vaporisation behaiour in the Lotus twin cam much like fuel injection (which is why you never should have to use the choke). Fuel injection is fun to play with but I suspect not really needed to keep you twin cam running.

As towhy your car cuts out after a down hill run, sounds like going over rich due to flooding if fuel pressure builds up during periods of low consumption but I would expect a similar problem when just sitting and idling. It may be due to going over lean due to air leaks around the o-rings when running the engine at very high vacuum during the overrun.

Rohan

[type26owner]

Rohan,
I haven't done any tuning on any Webers for several years until recently. Remembered in the shower this moring I had this problem before and was able to diagnose it by stumbling upon the solution first. My driveway is steeply pitched and I observed that if I tuned the idle while the car was nose up it wouldn't run well when back on level ground. What I discovered is if I tuned it with the nose down then it idled okay at any attitude. I suspect it has to do with the way the fuel level changes because the float pivot is positioned forward on the DCOE's.

My FI system is definitely a novelty toy and I do love to tinker.
Thanks
Keith

[type26owner]

Well, I've been several weeks now testing the NGK BP5ES plugs and am pleased to say they are exactly the right temperture range for my twincam. They appear now like the ideal ones on the ngk website.

Rohan, my inside sources say the new California Reformulatred fuel is to be at least 30-40% ethanol and I'm pretty sure ALL carbs are going to ice up with that much alcohol. Besides there's the issue that alcohol is a severe oxidizer and the metal fuel system is going to corrode and dissolve pronto.
Keith

[rgh0]

Keith

Glad to hear the hotter plugs seem to be doing the job. If California is really going to a fuel with 30 to 40% ethanol all I can say is good luck, as it is not practical for almost all engines ( carburettor or fuel injected) not specially built for those levels of alcohol.

Any carbureted car will certainly run to lean without rejetting. Corrosion will eat out the system not so much from the alcohol but the water it brings with it. The historic race cars here designed to run on 100% alcohol have huge jets to get the volume of fuel required through to get te right air fuel ratio and have to be drained between race meeting to stop corrosion.

Rohan

[gjz30075]

This thread had me thinking of my situation with symptoms similar to Keith's (in the first post). I, too, was running BP6ES's and have since switched to BP5ES's and the car runs fantastic. Absolutely no hesitation upon first acceleration after sitting at a light. On the 6's, the car was horrible to drive after sitting in traffic. It took several miles for the plugs to clear. With the 5's, no such problem. Thanks Keith and Rohan.

Greg Z.