Spark Plugs

[docc]

The Sport continues to stumble at idle and generally act lean. A careful retune helped, but the burble remains. Short of adding a Power Commander and doing a valve job, I'd like to try all the simple stuff.

 

Switching to a non-ethanol high octane fuel doesn't appear to have made a real difference.

 

Before having the CO tweaked, I'll change the plugs and adjust the valves even though it's only been about 4500 miles.

 

What is it, exactly, about "colder range" sparkplugs? They don't really make the motor any cooler? Would they help the borderline lean condition?

[Garsdad]

The Sport continues to stumble at idle and generally act lean. A careful retune helped, but the burble remains. Short of adding a Power Commander and doing a valve job, I'd like to try all the simple stuff.

 

Switching to a non-ethanol high octane fuel doesn't appear to have made a real difference.

 

Before having the CO tweaked, I'll change the plugs and adjust the valves even though it's only been about 4500 miles.

 

What is it, exactly, about "colder range" sparkplugs? They don't really make the motor any cooler? Would they help the borderline lean condition?

 

Straight from Wikipedia:

 

Heat range

 

The operating temperature of a spark plug is the actual physical temperature at the tip of the spark plug within the running engine. This is determined by a number of factors, but primarily the actual temperature within the combustion chamber. There is no direct relationship between the actual operating temperature of the spark plug and spark voltage. However, the level of torque currently being produced by the engine will strongly influence spark plug operating temperature because the maximum temperature and pressure occurs when the engine is operating near peak torque output (torque and RPM directly determine the power output). The temperature of the insulator responds to the thermal conditions it is exposed to in the combustion chamber but not vice versa. If the tip of the spark plug is too hot it can cause pre-ignition leading to detonation/knocking and damage may occur. If it is too cold, electrically conductive deposits may form on the insulator causing a loss of spark energy or the actual shorting-out of the spark current.

 

A spark plug is said to be "hot" if it is a better heat insulator, keeping more heat in the tip of the spark plug. A spark plug is said to be "cold" if it can conduct more heat out of the spark plug tip and lower the tip's temperature. Whether a spark plug is "hot" or "cold" is known as the heat range of the spark plug. The heat range of a spark plug is typically specified as a number, with some manufacturers using ascending numbers for hotter plugs and others doing the opposite, using ascending numbers for colder plugs.

 

The heat range of a spark plug (i.e. in scientific terms its thermal conductivity characteristics) is affected by the construction of the spark plug: the types of materials used, the length of insulator and the surface area of the plug exposed within the combustion chamber. For normal use, the selection of a spark plug heat range is a balance between keeping the tip hot enough at idle to prevent fouling and cold enough at maximum power to prevent pre-ignition leading to engine knocking. By examining "hotter" and "cooler" spark plugs of the same manufacturer side by side, the principle involved can be very clearly seen; the cooler plugs have more substantial ceramic insulators filling the gap between the center electrode and the shell, effectively carrying off the heat, while the hotter plugs have less ceramic material, so that the tip is more isolated from the body of the plug and retains heat better.

 

Heat from the combustion chamber escapes through the exhaust gases, the side walls of the cylinder and the spark plug itself. The heat range of a spark plug has only a minute effect on combustion chamber and overall engine temperature. A cold plug will not materially cool down an engine's running temperature. (Too hot of a plug may, however, indirectly lead to a runaway pre-ignition condition that can increase engine temperature.) Rather, the main effect of a "hot" or "cold" plug is to affect the temperature of the tip of the spark plug.

 

It was common before the modern era of computerized fuel injection to specify at least a couple of different heat ranges for plugs for an automobile engine; a hotter plug for cars which were mostly driven mildly around the city, and a colder plug for sustained high speed highway use. This practice has, however, largely become obsolete now that cars' fuel/air mixtures and cylinder temperatures are maintained within a narrow range, for purposes of limiting emissions. Racing engines, however, still benefit from picking a proper plug heat range. Very old racing engines will sometimes have two sets of plugs, one just for starting and another to be installed once the engine is warmed up, for actually driving the car.

[docc]

Thanks,

 

I think I will try a colder plug and see they look any different after 4000-6000 miles.

[dlaing]

Before having the CO tweaked, I'll change the plugs and adjust the valves even though it's only been about 4500 miles.

I usually adjust my valves every 2000-3000 miles and I see at least one valve being a bit off every time. (of course I may have a recession problem.)

 

I wish CO meters were cheaper, because then we could all have one, and not just depend on luck.

 

Valve adjustments are easy and fun Just pour yourself one straight up and follow up with throttle balancing and happy days!

If it is still acting up and you can't get to a CO meter, try a different air bypass setting and see if it gets better or worse. You can always set it back if you note what it was set to.

[Dan M]

Thanks,

 

I think I will try a colder plug and see they look any different after 4000-6000 miles.

 

 

docc,

 

It won't change your running. It is about plug life more than anything. A hotter plug will stay cleaner in a rich enviornment. Going too hot for a particular mixture may cause knocking from pre-ignition. If your plugs are white and blistered looking around the insulator you may want to go cooler or if they are dark and sooty you may want to go hotter but both are indicators of improper fuel mixture. The real fix is to get the mix right.

[docc]

Good point on the mixture. I'll get the bike to Corse Motorsports and tweak the CO.

[Steve G.]

The Sport continues to stumble at idle and generally act lean. A careful retune helped, but the burble remains. Short of adding a Power Commander and doing a valve job, I'd like to try all the simple stuff.

 

Switching to a non-ethanol high octane fuel doesn't appear to have made a real difference.

 

Before having the CO tweaked, I'll change the plugs and adjust the valves even though it's only been about 4500 miles.

 

What is it, exactly, about "colder range" sparkplugs? They don't really make the motor any cooler? Would they help the borderline lean condition?

 

Stumbles at low revs you say? Are your tappets adjusted to European specs, or the quiter, smaller, and problematic North American specs?

Steve

[docc]

I'm running 0.006/0.008, but it's been almost exactly 4000 miles. I'll give the lash a check before I change the plugs.

[nose2wind]

I'm running 0.006/0.008, but it's been almost exactly 4000 miles. I'll give the lash a check before I change the plugs.

 

Docc, I would check the valves for sure. Back when mine was running bad I didn't check the valves because I had done recently. After taking the bike to MPH. I was surprized when they said the biggest problem was the exhaust valves to tight! Oxygen sensor was out too. MPH just started from scratch and re-tuned the entire bike. It runs great with the one exception being when the engine is hot it can stumble from high rpm's down to idle. This could be the timing chain tensioner that has been discussed.

 

 

 

Good luck

 

D

[docc]

The intakes were 0.007. I was glad to see they hadn't tightened up. I reset to 0.006/0.008 and rode about 30 miles. Still burps, occasionally, hot at idle. I changed the plugs (colder:BPR7ES), still burps occasionally at idle or just barely cracking the throttle. But just when it's hot. I do have high expectations . . . It runs absolutely great otherwise!

 

I'll try setting the CO with an Axone. After that I'm moving , with the Sport, to Mandello and see if it's just climate.

[dlaing]

Are you saying it runs better, but still not perfectly, after the colder plugs were installed?

 

I am pretty sure changing intakes from .007 to .006 won't reduce lean stumbling.

Changing from .0007 to .007 would reduce lean stumbling!!!

[docc]

It seems as though every thing I've done has made an incremental improvement. At this point, it will get the occasional *cough* sitting at idle or rolling along in the 'lean' rpm range (4000-4500).

 

It's worse when the ambient temperature is higher or if the motor is hot (stuck in traffic).

 

I'm curious to see if it's worse when I run out of this high octane leaded race fuel and go back to 10% ethanol.

[Dan M]

It seems as though every thing I've done has made an incremental improvement. At this point, it will get the occasional *cough* sitting at idle or rolling along in the 'lean' rpm range (4000-4500).

 

It's worse when the ambient temperature is higher or if the motor is hot (stuck in traffic).

 

I'm curious to see if it's worse when I run out of this high octane leaded race fuel and go back to 10% ethanol.

 

 

Race fuel is good for avoiding knock but with the higher flash point it is also harder to ignite. Under certain conditions, like if your mix is lean it may be more likely to misfire with the high octane.

[docc]

Good point on the higher octane. It did flame out idling at a stop in the heat today.

 

I may try some 89 and see if it trades stumble for ping.

 

Is the ethanol harder to ignite?

[docc]

Go figure . . .It runs better on 89 octane. Still, I've never seen it so lean.