Ultimate Coil and Iridium PLugs

I completed a road test for the Iridium spark plug to check the gas mileage. Here are the results along with a comparative to other plugs and coils:
Summary of highway gas mileage using various coils and plugs. The 17-6903 coil is the new "Ultimate Coil" with the towers on the side.

Motorcycle:1981/H
Carbs: Stock BS34's
Exhaust: EMGO 27" reverse cones
Air Filters: Paper element replacements for stock filters
Fuel: 93 Octane
Ignition system: PAMCO 60 degree (except test 1 is 90 degree)
Plug wires: 5K caps


Test, Coil, Plug, MPG, % Increase, From stock, Main Jet

1, Stock , BP7ES, 57MPG, 0, 0, 132.5
2, 17-6822, BP7ES, 60MPG, 5.20%, 5.20%, 132.5
3, 17-6903, #63, 66MPG, 10%, 15.70%, 135
4, 17-6903, BPR7EIX, 69MPG, 4.50%, 21%, 135

Note: Same 60 mile test route for all results.
Note: Edited to show BP7ES plugs for test 1 and 2.

Same pump used to refill after each run.
The results for the Iridium plug are impressive. More than I would have thought for just a change of plugs. Of course, this means that more of the fuel is being ignited in the cylinder, so there will also be a corresponding increase in power as well. Because more of the fuel is actually ignited, you can feed more fuel with a larger main jet to further improve performance without sacrificing fuel economy. I installed 135 jets for the last two runs, as shown

Pete, thanks for this.

Is there a specific part number that would correspond for a stock '73? I recall you (I think) had posted some good plug stats, but it was on the old forum.

TeeCat,

Was this it?

You may want to consider changing over to 5/8 Hex spark plugs instead of the stock 13/16 because of the greater variety of new plugs that are available in the 5/8th hex style. Here is a quick guide to plugs that are compatible. They are all resistor plugs, as are all new design plugs.

NGK Stock

FR4 5155
FR5 7373 (Hotter)

NGK Stock

BCPR7ES
BCPR5ES 7496 (Hotter)

Bosh Stock

FR8DPX 4202 (Platinum)

Bosch Stock

FR8DCX 7557
FR10DCX 7563 (Hotter)

These are 13/16ths

AutoLite #63

NGK BPR7EIX Iridium

NGK BPR8EIX Iridium ('70 - '72)

I have tested all of these plugs with the PAMCO ignition, of course, and they all work great, but the Iridium plugs actually produced a 4% increase in gas mileage, which equates to better fuel burn and potentially greater power.

Pete, this is it, thank you. I was considering changing over to an Iridium plug in my '73, and from your list, I gather that I could use the NGK BPR7EIX Iridium that you list here, though it's apparently still a 3/16ths.

I don't want to commandeer the thread, but part of the reason I ask is because I was trying to read my plugs today. Both are exactly alike, and appear to be oil free, which I'm happy about because it seems that my motor has good oil control. However, though they are dry (not cakey or sooty) they seem a bit dark on the electrode and the face of the threaded rim. They're not full black really... but not "tan". Also, the insulators don't seem to be blistered or anything, but the porcelain is black on one side, and white on the other, and whiter nearest the electrode.

So, I'm thinking I might be a tad rich still (PAMCO, pods, stock jetting, stock headers and short reverse cones, pilot screws 3/4 turns out). I was thinking of going in on the pilot screws a little, but I'm wondering whether an iridium plug might clean up my burn just enough to get me where I want to be.

Thanks.

Thought we had some plug pics on the other forum... can't find any here yet, unless I missed something.

TC

TeeCat,

Well, the Iridium does burn more of the fuel, which would lead one to believe that it will burn more of the fuel in a rich condition and result in a cleaner plug. In my testing, as an example, I was able to increase the size of the main jets and still got better mileage.

The down side to experimenting with the Iridium plugs is their cost, so generally, you would prefer to have a good plug read before installing the Iridiums, or have access to an old fashioned abrasive plug cleaner.

The Autolite 64 which I use at 8-1.......is one step hotter than the BP7ES...maybe even a half a hair hotter by measuring the length of the insulator than the BP6ES....think I will try the Iridium equivalent to the 64........thinking it is the XP64 in Autolite....would have to measure the insulator to be sure...The ole 64 does good though.......with a little color........55mpg or so.........

xsjohn

Pete -

I suppose I'm not averse to putting a more expensive set of plugs in an increasingly rare bike that gets lightly ridden and that I have gone to the trouble and expense of bringing back from the dead. Maybe I'll go in about an 8th or quarter turn on the pilot screws and check them again, but it would seem that the more complete burn offered by Iridiums can't hurt, maybe. If nothing else, it will assuage my curiosity. I'll see if I can get these locally.

And John, thanks. Mine are darker than that, for sure, and not light for the full circumference of the insulator like yours. Maybe the light part on mine is where more combustion occurs or something. *shrugs*

Pete, do you mean 17-6803 ig-coil from mikes? or the 17 6903 as you posted?(can't find this number at mikes)

at mikes the coil (17-6803 cost $34 wich makes €26, in holland the same coil will cost me €43 at heiden-tuning)??????

Trebor,

I am referring to the new 17-6903 coil from MikesXS which at this time is only available in the new kits.

What did you have your plug gaps at for those tests, just curious.

NoValidTitle,

With the stock coil and the 17-6822 coil I used the stock gap .028 with NGK BP7ES plugs and 5K caps.

With the 17-6903 gap was .040 using either an Autolite #63 or the Iridium plugs.

And, I just noticed that I listed the wrong plug for the stock coil and the 17-6822 tests, so I'll go up there and change that.

Member Sundie recently tried the Iridium plugs @ .040 and he reported some missing at higher RPM's. I'm awaiting further word from him on the setup, so a setting of .035 might be a better choice.

I had the Iridiums gapped to 40, and seemed to have issues past 5000 rpm. I regapped to 30, and the issues moved farther up the rpm scale (which led me to believe that it went away - but it turns out i just wasn't flogging it enough).

I'm currently experimenting with different jets/needle positions in the carbs to see if fuelling that high up is the issue. It *does* appear to be fuel, rather than spark related, since i went back to stock jets (135) and dropped the needle from the middle (third) position to the 2nd from the top (thus leaner) and hesitation moved even farther up (i'm up to about 6500-7000 now). I'm considering lowering the needle another notch - i believe i have mid range bleed over. (all of this is totally beside the topic)

Pete, i haven't updated that thread simply because i want to get the problem solved, then try moving back to 40 to see what happens.

OK. Have you checked the coil resistance from cap to cap to be sure that both plug wires are making contact in the coil and that the caps are not open?

Yep. 24.5k cap to cap. I'm certain it's a fuel issue - else it wouldn't move when i changed the fuel setup. Of course, i'm tuning in the 6500+ range now, so it's a bit extreme.

Okay, an update. took a while, because it turned out to be an in tank filter had fallen off my right petcock. this allowed grit to randomly get into the bowls. I only really noticed this when i fully rebuilt my carbs, then the problem seemed to go away for a few days, then came back with a vengeance after a single hard pull away form a light (so bad that the right hand cylinder refused to fire). On gut feeling, i pulled the bowl, and despite being cleaned 2 days previous, there were considerable bad bits in there. I put a temp clear filter on to see what that might tell me, and it filled almost immediately.

Took my tank off with the intention of simply flushing it out, and when i took the pet cock off... see attached picture. Ends up it was rolling around in the tank. Fished it out, 1194'd it back in place (which was a really snug fit - not sure why it fell out in the first place. the 1194 will ensure it stays there), flushed my tank anyway, and everything has been fine. So fine that it pulled all the way to 9k (accidentally) today.

I haven't re-gapped to .40 yet, but that's my next thing to do.