Spark plugs

[funky]

Hi All
I have pretty much come to the end of my build in terms of running in the engine and jetting the carbs.
I have been reading up on Spark plugs which has made me think about if it would be a good idea to go up on the heat rating which in the world of Spark plugs means a colder plug .....I think ..... is this right.

My rationale is that my engine is now a 707cc, rebord standard head and block not bigbore kit. I have BS34s Mikuni, Pamcoe electronic egnition, high voltage coil.
Plugs NGKBP7ES being used. also have Iridium set that came with the pamcoe and have used them also.
As I have mentioned I have been messing about with the jetting, and am happy with how the bike is running, bar it takes a couple of attempts to start from cold with the choke on the first notch.

When inspecting the plugs through the process of rejetting, they went from an initial black sooty insulator and electrode,,, to rich,,, to a light brown with a black outer ring,,, getting there .... to where they are now, a light grey/brown electrode and insulator and a black outer ring.... spot on I beleive....

I am having a gut feeling that changing the heat rating may improve things or am i over thinking as i commonly do.
My Haynes manual states that NGK B8ES or BP7ES can be used. What do you fellas think.

All the Best Funky

 

[Uhlaf]

If I remember correctly the 8's were specified for the very early models (71 and 72?), while the 7 were later recommended for all following models.

Most people use the 7's, I'm still rocking my iridiums. There's also autolites and Bosch's to concider as well.

 

[gggGary]

What coil? IMHO opening up the spark gap a bit should help improve flame propagation if you have coils with enough umph. I think I bumped the gap up to .035 with a pamco controlled accel coil. Turned it into a "tire smoking monster".

 

[funky]

What coil? IMHO opening up the spark gap a bit should help improve flame propagation if you have coils with enough umph. I think I bumped the gap up to .035 with a pamco controlled accel coil. Turned it into a "tire smoking monster".

Hi GGGGRAY it funny you mention the gap i was just reading about that,,, I have that high voltage coil that came with the Pamcoe I am sure thats man enough ...I will try that first
As to the post previous by UHlaf my bike is a 1981 special so NGK BP7ES should be the right one but my engine is now a 707cc so more fuel is being drawn in on the induction stroke so that why i was thinking the way i was... thanks for the reply

 

[hardrock785]

what gary said

 

[funky]

No offence GGGary as I hold you in high regard as to your knowledge on these matters but ,,,I would like pamcoe pete to jump in here as i feel he would know about optimising plug gap for the high voltage coils that come with the pamcoe, well mine i mean. I have the single coil high voltage version pamcoe kit and the standard mechanical ATU... Would an increase to .035 from .028 make a differance ???????

 

[gggGary]

No offence taken, it's just a WAG on my part. Pete has some performance figures floating around somewhere, he felt he could show increased performance and fuel mileage with a series of ignition upgrades after a series of test runs.

Post #2 here summarizes it.

 

[funky]

yes I read that it was mainly about the iridum plugs. this is such a learning curve and good fun i may add I want to be burning all the fuel in the chamber so bigger spark should do that .....I also read that increase in plug gap puts extra stain on the coil so it may get hot. its a good thing i have good air flow round mine i did think of that when i fitted it .... i could be very wrong though lol we will see Plugs set at .035.... All dark now where i live and raining so test run tomorrow .

 

[5twins]

Going up on the heat rating would be a hotter plug, not a colder one. That would be a 6 series NGK. The 8's originally speced are colder than the 7's recommended now. If you use 8's, they will run darker. The other thing to consider is the type of electrode design. The "B" series is a standard normal plug design. The "BP" series has a projected tip. The center electrode sticks out more from the threaded body of the plug. This places it farther into the combustion chamber and exposes the spark to the fuel/air mix more. This is supposed to give a better and more complete burn. Yes, increase the gap, but don't go overboard. The .035" mentioned is probably the most I would go. I run .032" and it seems to work fine.

The choke works best when on full. The bike may start easier and quicker when stone cold if you try that. I swapped in an extra set of carbs to test. The bike was harder to start cold with them. It was a quick easy cold starter with the other set. I noticed the chokes weren't opening fully. A little bending of the bracket that holds the choke lever open (BS38s) made them open fully and the bike became an easy cold starter again.

 

[funky]

Thanks 5Twins nice to hear from you again ...I did get confused about this hot and cold plug thing .... i beleive its to do with the size of the insulator...
This is the official explination from NGK
A low heat range (or hot) spark plug typically has a long thin insulator nose which will heat up easily however will not dissipate readily to the metal shell . Conversely, a high heat range (or cold) spark plug has a short thick insulator nose which will dissipate heat much easier.
LOL i still get confused ...Lets see the lower the number the qicker the plug gets hot so this is a hot plug ....
The higher the number the greater the resistance to heat so this is a cold plug .... I think lol
Summery the smaller the engine the hotter the plug (low Numerical value small insulator ) and viser sersa The bigger the Engine the more heat it prduces the colder the plug ( Higher numerical value large insulator)
The insulator protects the plug from the heat produced by the engine... the confusing thing here is that more insulator colder the plug, higher the numerical value. ,,,, so think of the reverse to why we insulate our lofts.
Its about keeping the heat away from the core of the plug... ithink if this is not right I give up attempting to understand ......

 

[5twins]

I don't give this too much thought. I run what is speced and/or recommended. With my 650, that is the factory recommended BP7ES. They have always run well for me and I see no need to change. I don't use any of those more expensive fancy platinum or iridium plugs. I have found this old engine design to be rather tough on plugs, wearing them pretty quickly. I usually change them out about every 4K miles. I don't mind this since the standard NGK is only about $2 at the auto parts store. It probably would bother me if these were the $8 fancy plugs, lol. Yet another reason I don't use them I guess.

If Pamcopete chimes in here, he may explain how the iridiums don't perform up to their full potential on a single coil with dual outputs. Something about the direction of current flow. Only one of the plugs will perform as its high price warrants, the other will act more like a normal (cheaper) plug.

 

[funky]

Yes I have had that discussion with pamcoe pete, ist to do with the polarities if i remeber... I have been using the NKG BP7ES and they have served me well. I have the Iridium ones that came with the Pamcoe and have used them but to be honest I would stick with the NGK's Thanks 5twins all the best mate

 

[5twins]

In a 4 stroke, the plugs usually burn pretty clean and wear evenly. It's hard to tell when wear has occurred unless you have a brand new plug on hand so you can compare them side by side. What happens is the center electrode wears shorter. You can readily see this comparing an old and new one but won't notice it looking at an old one by itself. That's why you should always have a new set of plugs on hand. You need them for a "testing tool" besides as replacements.

 

[CDNTX650]

If you run the spec plug and they are cleaning them selves well with proper jetting no reason to switch. You can run a step colder to a bp8es if you do Lots of hot weather highway running. I run autolite 64. Iridium in the xs seems to be a wallet drainer more Than anything.

 

[funky]

Going out on the bike for a little run Gap set at .035 NGK BP7ES.. will let you know how i get. Thanks for all the replies...
Oh that plane Pamcoe pete had was the same plane as in the film BAT21 there Awsome....
All the best Funky

 

[funky]

Well had a good run out that made a differance not sure what to do now though took the plugs out and they were initially light grey colour now there more of a tan brown. I did richen the needle jet , moved it from slot 3 to 4 from top. It not overly rich and seems to burn better with the iridium plugs as the NGK BP7ES were slightly darker. I think i will play with the plug gaps a bit more and get some new NGK's and try them as the one i have been using have about 1000 miles on them and have been cleaned about the same amount of times.

 

[5twins]

The auto parts stores around here sell them in a 4-pack. That's what I usually get, two to use, two for spares. As you probably are aware, you need to check and gap them. They usually come set really big (for car use).

 

[650mark]

fwiw, I've used the iridiums in all of my xs650's for some time with good results. the bikes all have had stock ignition systems, and with the iridiums they started much more quickly and idled better. more power? not so you could notice. better mpg? no. faster speeds? no. run hotter or cooler? nope. just better starting either dead cold or warmed up. worth the extra few bucks to me and I've never replaced one once installed. as for one cylinder performing better than the other with a single coil/dual output, don't know. but I've never had one side of the bike pass the other side

 

[pamcopete]

Going out on the bike for a little run Gap set at .035 NGK BP7ES.. will let you know how i get. Thanks for all the replies...
Oh that plane Pamcoe pete had was the same plane as in the film BAT21 there Awsome....
All the best Funky

Now you've done it...brought back the fond memories of my flying days and the Skymaster. I had two of them. The first one was heavily damaged in a hurricane and totalled, but someone actually bought it and flew it down to Florida. I had an engine failure in each caused by maintenance. Blew the #5 cylinder clean off the rear engine on the first one with a 50 hour engine. Second incident was on the way home from picking up the airplane at Big Bear Mountain, CA. Just lost all it's oil over Greenville, MS when the oil filter came loose. It's a very easy airplane to fly, very forgiving and it always got me home, even on just one engine.

This is a file photo. Not mine, but exactly the same.

You can use a wider gap with the ultimate coil because it produces so much of a higher voltage. Probably not such a good idea with something less. Basically, you can assume that a coil with less than 3 Ohms primary resistance will allow for a wider gap.

Keep in mind that the fuel mixture is a mixture of air and fuel molecules that are not equally proportional. There can be clusters of fuel and clusters of air and clusters of fuel / air in the correct proportion, so using a wider gap simply exposes more of the mixture to the initial spark and increases the odds of igniting more clusters of air / fuel mixture which then form a larger kernel of flame that goes on to ignite the rest of the mixture in the cylinder. Sort of like starting the camp fire with a bigger match.

I ran some tests some years ago by running a set number of miles on a perfect day and changed the coils and plugs after each run. Here are the results:

Now, keep in mind that I was trying to get good gas mileage, so as they say, your results may differ. I inflated the tires to 32 PSI, never went faster than 55 MPH and the route was mostly open road with very little stop and go. I also refilled using the same pump after each run.

 

[weaselbeak]

Rule of thumb back in the day was to use the 7's for all around riding, and 6's for mostly in town or low rpm. We used 8's if we were doing a lot of highway time. My experience with dirt bikes was to have less fouling with the 6's. Now I use one plug in my Moto Guzzis, my XS650, and my Virago with excellent performance, no fouling and long life. And that is the Autolite AP63. They are resistor plugs, so resistor caps are not used. I have not found a better plug.