Spark Plug Question

[sodakproud]

I have a 78 XS11 Standard. I "thought" that I had replaced the spark plugs last year with NGK BP7ES plugs. So I ordered some more. They came and they are NGK BP8ES plugs..... So did I get the wrong ones or should I have gotten 7's? Will the 8's work? Also the caps have seemed to gotten plugged off in the wires.... What can I guy do about that problem?

[CatatonicBug]

You "ordered" plugs?? Why? Just take your plugs to the local auto parts store and tell them you "need 4 of these". I don't know whether the 8's will work, but I'm confused about the last part of your question:

Also the caps have seemed to gotten plugged off in the wires

The wires have caps on the end that can be pulled off the wires with a twist. Those caps then just slide over the tops of the spark plugs. You can cut 1/2" off the end of the wire to help with the conneciton before re-attaching the caps if needed. Otherwise, just press them on firmly and twist.

[sodakproud]

Yeah I live 100 miles away from a Motorcycle dealer... IE South Dakota. Crap on the 8's... I'll have to re order some tomorrow or something.... Thanks for the cap stuff. Oh and I found out that its a 1979 Standard... Damn registry is wrong.

You "ordered" plugs?? Why? Just take your plugs to the local auto parts store and tell them you "need 4 of these". I don't know whether the 8's will work, but I'm confused about the last part of your question:



The wires have caps on the end that can be pulled off the wires with a twist. Those caps then just slide over the tops of the spark plugs. You can cut 1/2" off the end of the wire to help with the conneciton before re-attaching the caps if needed. Otherwise, just press them on firmly and twist.

[CatatonicBug]

Yeah I live 100 miles away from a Motorcycle dealer...

Avoid MC dealers at all cost. You can get most of these "consumable" parts from a regular "Car parts" store. They are much cheaper, and easier to find.

[petejw]

The stock plugs for these are the 6s
going to 7 is a colder plug and would be fine if you
live in an area where its pretty hot.
I wouldnt use the 8s.

[WMarshy]

I agree, 8's are too cold of a plug. Lower numbers are hotter plugs, read what it means here.

[WMarshy]

Reading Plugs

Here's a great explination on how to read your plugs.

[Ivan]

Instead of waiting on a new set of plugs, I would try the colder plugs. They may run just fine. Heat range is 3 parts voodoo, 1 part mysticism and a smattering of science. On a spark fired engine, the spark does the work of ignition, so the heat range is mostly for flame kernel control. The cooler plugs will make a smaller kernel that has a more controlled flame front. It will help somewhat with detonation issues, but will cause fouling much easier.

Basically, if it runs with them and your plugs don't foul up (with a proper mixture, of course) they are fine. If your mixture is right and they still foul, get hotter plugs. If your mix is rich and you have black sooty smoke out the exhaust but the plugs stay white, go for cooler plugs.

In my experience, heat range is one of the LEAST effective changes that can be made. Even different octane levels in the fuel have a more drastic effect than heat range.

Just a thought.

[petejw]

the experience i had using different heat
ranges was with the 5s the engine pinged
and with the 7s the acceleration wasnt as strong,
the 5s i tried in winter and the 7s i tried in summer.

[clcorbin]

Instead of waiting on a new set of plugs, I would try the colder plugs. They may run just fine. Heat range is 3 parts voodoo, 1 part mysticism and a smattering of science. On a spark fired engine, the spark does the work of ignition, so the heat range is mostly for flame kernel control. The cooler plugs will make a smaller kernel that has a more controlled flame front. It will help somewhat with detonation issues, but will cause fouling much easier.

Not quite. The heat range of the plug actually has nothing to do with the flame kernel. It basically describes how long the thermal path is from the tip of the plug to the "nut" of the plug. The "hotter" the plug, the longer the path is. The longer this path is, the more time it takes to transfer energy from the top to the cylinder head. This causes the tip of the PLUG to be hotter or colder under a given circumstance in the combustion chamber.

If you have a cold plug in a "cold" chamber that is running rich, it will get deposits building up on it quickly and can and will foul. The other extreme is even worse. If you run too hot of a plug in a hot running engine that is running a bit lean (hot mixture), it WON'T foul, but the tip of the plug can get hot enough to cause preignition/detonation.

This isn't USUALLY too much of a problem for normally aspirated engines, but once you start going to forced induction or nitrous, things can get VERY expensive very quickly if the plug is too hot. Us NA guys are usually just worried about getting the plug hot enough to burn off the deposits without being so hot it can lead to preignition. Thankfully, we have a much wider margin than our forced induction neighbors.